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# Jonas Zmuidzinas

Jonas Zmuidzinas

### Merle Kingsley Professor of Physics; Director, Caltech Optical Observatories

##### August 20, 2021

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Friday, February 18, 2022. I'm delighted to be here with Professor Jonas Zmuidzinas. Jonas, it's great to be with you today. Thank you so much for joining me.

JONAS ZMUIDZINAS: Thank you very much. It's good to be with you, too.

ZIERLER: To start, your name. It's a very interesting and unique last name. What's the national origin of it?

ZMUIDZINAS: Lithuanian. But it's a little more complicated. It's actually, you could say, a Lithuanianized Polish last name. If it was purely Lithuanian, it would probably be Žemaitis, which means a person from the Žemaitija (Samogitia) province of Lithuania. The Polish word for that region is Žmudz, and Žmuidzin or Žmuidzinas is a person from that area, except with the Polish root and then the -as tagged on to make it kind of Lithuanian. What I've been told is that likely, what was going on is that Polish priests in the southern part of Lithuania went around giving people last names because they didn't have any. [Laugh] Several hundred years ago. I'm not sure exactly when that would've been. That's apparently how our family got that name, they were farmers in Keturvalakiai, which is about 30 kilometers from the current border between Lithuania and Poland.

ZIERLER: At a more official level, what is your title at Caltech, and what are your affiliations?

ZMUIDZINAS: I'm a Professor of Physics. I have a so-called chair, Merle Kingsley Professor of Physics. I'm also now serving as the Director of the Caltech Optical Observatories, which includes Palomar and Keck, oversight on TMT. I also serve on the board of the Thirty-Meter Telescope project as part of that duty.

ZIERLER: Do you have an idea of who Merle Kingsley was and if there's any possible connection to your work?

ZMUIDZINAS: I don't think there's a particular connection. I'm embarrassed to say it's been a while since I read her biography. She was obviously a donor to Caltech. I don't remember a whole lot more than that. I'll have to go refresh my memory. But the name Kingsley is attached to a few things at Caltech, including this professorship. (Merle Kingsley Elkus was a philanthropist, a Caltech trustee and major contributor.)

ZIERLER: Just as a snapshot in time, what are you currently working on? What are some of the big projects in your portfolio?

ZMUIDZINAS: I'd say what keeps me busy is being director. That takes up a fair fraction of my time. As part of that, we're working on various instruments for Palomar and for Keck. We were fortunate enough to receive late last fall a rather major donation towards the construction of instruments for Keck to the tune of something like $71 million. We're starting to work on exactly what we might do in detail. That requires a fair bit of planning. We're having a faculty retreat in a week to discuss some of that. But apart from that, I still have projects that go back to my time before being director, in longer-wavelength astronomy and astrophysics, the research area I've spent most of my career in, involving developing superconducting detectors for those wavelengths. I still have a fairly active lab that is used by a number of students, a staff scientist Steve Hailey-Dunsheath, and a scientist from JPL, Matt Bradford, who do most of the heavy lifting in keeping that operation running. I mostly just kibbitz once in a while. ZIERLER: Another timely question. I wonder if you've had a chance to look closely at the recently released decadal report, Astro2020, and if there are some major takeaways, for you personally, for your field, and for Caltech institutionally. ZMUIDZINAS: Sure. There are two major areas, ground-based astronomy and space. Let's tackle space first since that relates to JPL. The decadal survey makes recommendations for different classes of projects, large, medium, small, you might say. There were four large potential space missions that the decadal survey committee reviewed, two targeting the optical and near-infrared wavelength region, you could say the traditional wavelengths for astronomy, then there was a mission for much shorter wavelengths, an x-ray mission, and then there was a far-infrared mission, much longer wavelengths. I participated on the study team that developed the concept for the far-infrared mission. In fact, my involvement in that dates back quite a bit further. I was on a NASA roadmap committee in 2013 to look at the far future of astrophysics, and I was one of the few members on that committee interested in the far-infrared. Our report recommended that NASA consider a far-infrared mission of the kind that ended up being proposed to the decadal, and that was really the seed that got the study for the decadal going. I've been involved in that for quite some time, and it dates back even further, but that's the most recent history. That's in terms of large missions I was involved in. That far-infrared study received a good recommendation from the committee; however it was not ranked as the first mission to go forward. What was ranked as the first mission to go forward was a combination of the two optical and near-infrared missions. One was studied by JPL, one by Goddard. Those were the centers leading those studies. What the survey committee ended up recommending was some kind of a blend between the two, some kind of intermediate mission in terms of at least the size of the telescope. That was the top-ranked large mission, and I think it was not a big surprise that it ended up being the top-ranked mission, but it's also not going to happen very quickly. The decadal survey report recommended that perhaps in the 2040s, if I remember correctly, there would be a launch, so that's quite a long way away. In terms of somewhat smaller missions, the real major development was that the decadal report recommended what's called probe-class missions. This is a new thing for NASA astrophysics, which has been doing so-called flagship missions, very large missions like James Webb, many billions of dollars. And also small missions, a few hundred-million dollars, such as the SPHEREx mission that Jamie Bock at Caltech is leading. And in between, there's a wide-open gap. There has been in the past. The decadal survey recommended that NASA do missions at roughly the$1- to $1.5-billion scale, so that got a strong recommendation from the decadal, and NASA is moving forward with that concept. They're prepared to release an announcement of opportunity a year from now roughly with proposals due in April of 2023, so maybe four months after this announcement. (Perhaps not surprisingly, now there are indications that this ambitious schedule may be delayed.) There are only two flavors of mission that NASA is going to be requesting proposals for. One is far-infrared, and the other is an x-ray mission. That's actually, I think, a very exciting opportunity for JPL. This is something that has been in the works for a while. It's been clear to me for a long time that if you wanted to do an ambitious far-infrared mission, trying to do a flagship-class mission, many billions of dollars, as the first step was maybe not the best approach, although obviously if there was the chance to do it, you'd go for it. But it seemed to me that doing a somewhat smaller mission would be a more natural progression. There are a number of things that you need to do for the far-infrared mission. One is that the telescope needs to be cooled to a rather low temperature, to four Kelvin, because you're working at these long infrared wavelengths, and in essence, reducing the telescope temperature reduces the glow of the telescope in the far-infrared. The more you can knock that down, the more sensitive the mission becomes, the easier it is to see distant objects. That's number one. Number two, you need detectors that can make good use of the cold telescope. The detectors need to be extraordinarily sensitive. And that's another serious technical challenge. The only place to really demonstrate those kinds of detectors is in space. You just can't find an environment on the ground, a balloon, or so on that comes anywhere close to the very, very low-background, high-sensitivity you can achieve in space. Being confident that you have the technology in hand for those detectors, and that you can launch a$1- or $1.5-billion mission with confidence that it's going to work requires a lot of work ahead of time, and I would much rather be launching a$1- or $1.5-billion dollar mission with detectors that I was pretty sure were going to work than a$10-billion mission. [Laugh] Anyway, this probe is, in many ways, also the culmination of many years of work, especially in the area of developing the detectors that we invented some 20 years ago, which are the kind needed for this mission. We're very excited to have a chance to see them go on that mission.

ZIERLER: What's some of the exciting science that could happen as a result if this goes through?

ZMUIDZINAS: If you were to look at what wavelengths contain information about the universe across the spectrum, one way to characterize that would be to make a graph where, on the vertical axis, you would plot the intensity of the light, how much light there is, and the horizontal axis would be wavelength, how short of a wavelength you're talking about, what you would basically see on this graph are three bumps. There's a bump in the visible and near infrared, and that's just starlight, the light emitted from all the stars in all the galaxies throughout the history of the universe. Light that was emitted many, many billions of years ago gets shifted to longer wavelengths. This is the red-shift effect. If you look at a star today, a typical star would have a spectrum peaking in the visible, like our sun. You take that and shift it a little bit to longer wavelengths as you go backwards in time, as you go further in distance in the universe, and you get this bump that peaks in visible and infrared. That one is not surprising. We all know about stars and galaxies.

There's another bump at much longer wavelengths, wavelengths that are of order of a few millimeters in size. You could actually imagine what that wavelength looks like. It's easily visualized. And it's a huge bump, the biggest bump in terms of its height, the energy contained. That is the cosmic microwave background, the so-called echo from the Big Bang, radiation that was released when the universe was maybe 300,000 years old. That was when the universe finally became transparent to light. Matter stopped being ionized and became neutral. The free electrons in the universe joined with mostly protons to form hydrogen atoms. Once that happened, once the free electrons are gone, they can no longer scatter the light. The light can then travel for long distances without being scattered or absorbed. That's when the universe became transparent. That was about 13.5 billion years ago, around 300,000 years after the Big Bang.

That light, we see at millimeter wavelengths, and it's the biggest bump. In between those bumps, the starlight bump and the cosmic microwave background bump, there's a third bump, which lies in the far-infrared, and it was discovered only fairly recently, although there were lots of false starts in this area. But the definitive detection of this bump came only in the mid- to late-90s, so not very long ago. Essentially, it comes from starlight, but starlight which has been absorbed by interstellar dust. Galaxies, in addition to stars, contain gas and dust, which is the material from which the stars are formed. The dust can absorb the starlight. If you've ever seen a picture of the Milky Way, you may remember seeing dark bands across the center of the Milky Way. That's the dust in the Milky Way absorbing the starlight. What happens is, the starlight gets absorbed by the dust, and that energy from the starlight heats up the dust a little bit to temperatures that are maybe ten Kelvin or a few tens of Kelvin.

At that temperature, objects radiate at very long infrared wavelengths. They radiate that energy they capture from the starlight, it's released back by these dust grains in the far-infrared portion of the spectrum. You might say, "Why is this interesting?" It turns out that stars are born in great clouds of gas and dust. It's these clouds that gravity pulls together, and eventually, you assemble enough material under the action of gravity in a small enough region of space that you can form a star. But a newly formed star is still surrounded by this cocoon of material it was born in, this cloud of gas and dust. The light often cannot escape this cocoon because there's too much dust surrounding the stars. One of the things that you get to learn about by looking in the far-infrared is, you get to learn about star-formation and star-formation activity in a way that you can't see at shorter wavelengths because the dust is surrounding these newly formed stars. That is really one of the main reasons this wavelength range is interesting, because it's a way of probing the history of how all the stars in all the galaxies came to be, the history of star formation, how all that worked. It contributes information you can't get in any other way because of this shrouding effect of the dust.

One of the interesting mechanisms by which stars are formed is, if you have two galaxies, each of which already has some stars as well as gas and dust, these galaxies can run into each other if they get too close. They can basically collide. Depending on the details, they can actually end up merging after the collision. They don't go off and escape each other, they end up doing some kind of crazy dance, some interesting orbit, stars get flung out, there is stuff falling in, and eventually, what's left is a single galaxy that contains material from both galaxies. In this kind of event, the stars in the two galaxies actually don't run into each other. It's the gas in the two galaxies that actually collides. The stars just go right past each other because they're so small, there's very little chance that one star in one galaxy will actually hit another star in another galaxy. But the gas can collide very nicely.

When that happens, the gas gets compressed, it gets heated, it radiates away energy. When it loses that energy, gravity has an easier time pulling that material together, and you can have a burst of star formation as a result, where all of a sudden, you've compressed this gas and prepared it just perfectly for gravity to take over and have a whole bunch of stars being born all at the same time. You have this rather sudden event, where you have a burst of star formation, and that star formation is happening in these cocoons of dust. The only way to see it is at these long wavelengths. This is a long-winded description, but hopefully it's giving you some feeling for why this part of the spectrum is interesting. And there's a lot more. This is just one aspect of it. There's a lot more, but I think maybe you've heard enough about this. [Laugh]

ZIERLER: Moving onto the US ELT program, given your involvement with TMT and what this means for Caltech, what were you hoping the decadal would say, what has it said, and what's the path forward from where we are now?

ZMUIDZINAS: Well, the US ELT program, which is both the Thirty-Meter Telescope and the Giant Magellan Telescope projects, we were hoping to get ranked number one, and they did. That was, I'd say, a really exciting moment for both of those projects and for the US ELT program. Now, the question is, what happens next? The ideal situation would be that both observatories get built with TMT being built in the North and GMT being built in the South, in Chile. But both projects require quite a bit of funding in order to be able to be completed. In the case of the TMT project, the Thirty-Meter Telescope project, there's a very sensitive issue surrounding the site, Mauna Kea. There's been a lot of opposition, particularly from native Hawaiians, who have well-founded and longstanding grievances. It's a problem you might say that's quite a bit larger than the TMT. Nonetheless, I think it's an exciting moment, and it's a delicate moment for astronomy in the US. The Europeans are moving ahead pretty quickly with the construction of their very large telescope, and already the US is behind, at least in time. If the United States is to maintain parity or stay at the forefront in this part of astronomy, something needs to happen. We're hopeful.

ZIERLER: Do you think it's advisable at this point to continue forging ahead for a solution of consent in Hawaii? Or is it time to start thinking more specifically about the Canary Islands for TMT?

ZMUIDZINAS: The issue of Hawaii versus Canary Islands has been, let's say, under discussion for quite a long time now. I think the pros and cons of both sides are fairly well-understood. Hawaii remains the preferred site from a scientific standpoint in terms of the quality and suitability of the site for doing astronomy at those wavelengths. If it were possible to make a dent in the grievances of the native Hawaiians somehow as a result of the TMT moving forward, if there was a win-win solution, clearly that would be the ideal case. I remain hopeful that something like that can happen, but it can't happen just by the efforts made by the project. It's going to require help from the government at both the state and federal levels. Perhaps as a result of national interest as expressed by the decadal survey and seeing this project go forward, perhaps that's what's needed for both the federal government and state of Hawaii to really think hard about what could be done to find a solution where everybody benefits. That would be ideal. I'm hopeful that will be the case, but it won't be easy, that's clear.

ZIERLER: In terms of what's in the national interest, more locally, what are the stakes for Caltech regarding whether or not TMT gets built? How important is this for what Caltech has represented historically in astronomy?

ZMUIDZINAS: We're at an interesting point because this has happened in Europe some time ago, and now it's happening in the United States. If you look up to the mountains, you see Mount Wilson, and there you have the 100-inch Hooker Telescope, which was built as a result of donation by a philanthropist (Andrew Carnegie). Palomar, same story (Rockefeller Foundation). Keck, same story (Howard Keck). TMT, not the same story. In the US, we've had a tradition of private philanthropists supporting the largest optical telescopes. In Europe, some time ago, they decided their governments would join and support astronomy. They formed the European Southern Observatory, or ESO, which is the entity that built the very large telescopes, the VLT, consisting of four eight-meter telescopes in Chile, and now they're building the ELT, also in Chile. But it's a large, government-funded science project, whereas with the TMT, it was kicked off with philanthropy, with Gordon Moore's help. But it won't be finished in that mode. If it's going to be finished, it'll be finished as a result of federal funding. We're in the middle of making this transition that Europe made some time ago. We've reached a scale in astronomy where it seems that philanthropy isn't enough. What does this mean for Caltech? The Thirty-Meter Telescope simply won't have the same relationship to Caltech that, for instance, the Keck Observatory does, where Caltech is a big partner. Caltech will only be a relatively small partner in the TMT. It'll be important for Caltech astronomers to have access to TMT and there are a number of interesting science programs to be done. But as I said, things are changing. It'll be a proud thing for Caltech to have started this project, and to see it be completed, and to have Caltech astronomers have privileged access to it. But at the same time, it really is going to be a national and international facility.

ZIERLER: What's so exciting about the Thirty-Meter Telescope? If we can get beyond all of the administrative challenges with the collaboration, the political issues, if this telescope gets built, what will be exciting about it? What will we know about the universe that simply wasn't possible before?

ZMUIDZINAS: As with any telescope, there's a very broad range of science that can be done. I can't describe even a fraction of it. I'll mention a couple of things. The first thing is that one of the major goals is the study of exoplanets. I think you understand the problem of studying exoplanets. Exoplanets have been detected using various methods, for instance by staring at a star and obtaining spectra over the course of many years, looking for slight shifts in the wavelengths of sharp features in the spectrum. These shifts are interpreted as being caused by the motion of the star towards us and away from us, as a result of a planet orbiting around it. Measuring stellar motions through spectroscopy over many years is a way of inferring the presence of planets. But you're only seeing light from the star, you're not actually seeing the planet. It'd be really nice to see the planet. Not only that, it'd be nice to use the light you capture from the planet to start learning something about the planet.

The ultimate goal is to get enough information about the planet so that you can start to make statements about the possibility that there may be life, that the planet is habitable. In order to do that, you have to be able to separate the light from the star from the light from the planet. The difficulty is that, on the sky, the star and the planet are right next to each other. You need to block the starlight but not the light from the planet. And the contrast is ferocious. The brightness of the star compared to the brightness of the planet is an enormous factor. It can be around a factor of a billion. You have to do an exquisite job of blocking the starlight in order to be able to actually see the planet. That's one of the challenges. If you try to do this, one of the things that limits your ability is how sharp an image the telescope can make. If the star and the planet are all blurred together, you've got no chance to do this. Once you block the light from the star, because the light from the planet is in the same blur as the light from the star, you're going to block the light from the planet. You have to separate them, and that translates to making a bigger telescope.

One of the major goals for the flagship missions the decadal survey looked at in the visible and near-infrared, the ones studied by JPL and Goddard, was to do this kind of thing at visible wavelengths, to try to separate the star from the planet at visible wavelengths. Doing this from space has the great advantage that you don't have to look through our atmosphere, and you can make very sharp images because you don't have to deal with the earth's atmosphere. If you have a ground-based telescope looking up, it has to deal with the turbulence in the earth's atmosphere, which is what makes the stars twinkle, what makes the star images blurrier. One tool you have to fight that is called adaptive optics. That's the scheme where you have a special kind of mirror that you can adjust the shape of using perhaps several thousand different tweaks to it. You have devices called actuators on the back, and you change the settings on the actuators, and it slightly changes the shape of the mirror near where the actuator's located.

You change the surface of the mirror on the order of 1,000 times a second, and you do it in such a way to take out the turbulence that the atmosphere's imposing on the starlight so at the end of the day, you're getting a nice, sharp image. Well, that works, but as you can tell from the description, it's not an easy thing to do. It's tricky and complicated. At the end of the day, you never do as well as being in space. But if you have a larger telescope on the ground, and you play this kind of game, and you choose the right kinds of stars to look at, with the Thirty-Meter Telescope, you can do some very interesting things in terms of trying to study the light from the planet and separating it from the stars. That is, I'd say, a real major and very difficult science goal for the Thirty-Meter Telescope, the study and characterization of exoplanets. And there are others. Many of the other science cases also rely on this adaptive optics trick of taking out the atmospheric turbulence. The bigger the telescope, the sharper the image you can make. There are a lot of areas of astronomy where being able to get those really sharp images and being able to make sharp images of things that are rather faint gives you a very big boost over the ten-meter telescopes. Those are a few things in a nutshell.

ZIERLER: I asked about the stakes for Caltech institutionally. What about the generational stakes? In other words, as you well know, there's a real burst of interest in exoplanet research among graduate students and post-docs right now. Absent a viable US ELT program, both for the TMT and the GMT, at what point does exoplanet research hit a wall, that there simply isn't much more to do without these telescopes getting built?

ZMUIDZINAS: I think there's still a fair way to go. I think certainly over the next decade, there won't be any shortage of interesting work to be done. But what makes everybody so interested and work so hard in this field is this tantalizing goal of being able to characterize those exoplanets. The further out of reach that goal is, I think it does become harder to sustain interest. And you can already see that with the decadal survey recommendation on the flagship mission being pushed out to the 2040s sometime. I think the survey committee realized that to build a space observatory of the kind that could have a real shot at doing this job of characterizing exoplanets, it was going to take a lot of money and time because it's a really hard thing to do. But on the other hand, if you're starting graduate school today, you think, "Great, this is going to happen during my career." But if you're my age, you think, "I'm not sure I'll ever see that." [Laugh]

ZIERLER: Moving onto the administrative side, let's start with Caltech Optical Observatories. At a high level, what is its mission, and where does it fit overall with JPL and Caltech astronomy?

ZMUIDZINAS: As you know, Caltech has a rich and proud history in optical astronomy. Caltech Optical Observatories, or COO, is the campus organization that oversees Caltech's astronomical facilities in optical astronomy. That includes Palomar, Keck, and oversight on TMT. What, in practice, do we actually do? First of all, there's a staff of roughly two dozen people, half of which live on Palomar, and the other half commute, and they're responsible for keeping the observatory running and making sure we get science every night as much as possible. Simply operating and maintaining the observatory is a significant fraction of what COO does, at least at Palomar. At Keck, there's an organization in Hawaii, the W. M. Keck Observatory, and a director, Hilton Lewis, with a staff of roughly 120 people, and it's their job to do the same thing for the two Keck telescopes on Mauna Kea to get science every night to the extent possible. My role there is more oversight, making sure that the organization in Hawaii is doing the things that are important to Caltech astronomers, that the Observatory is being operated and maintained in a way that serves the interest of the Caltech astronomical community.

I serve on various groups, the science steering committee that focuses on the scientific aspects of observatory management, the so-called CARA board, California Association for Research and Astronomy, which you could say is the name of the mother organization. The board of that organization oversees the management of the entire observatory. I serve on that body as well. That means attending meetings, paying attention, trying to provide advice, and so on. Other than that, on campus, we have a very active group led by Rich Dekany (B.S. '89) with also roughly two dozen people, who are the engineers that design and build instruments for both facilities and have also been working on the design of instruments for the TMT. It's really an incredibly talented group of people that can carry an instrument concept from a little scribble on a piece of paper to being installed and producing data at Keck. Really impressively complicated pieces of equipment. I also oversee that group, try to make sure that the projects there are on track, that we have an interesting stream of work to be doing, etc.

ZIERLER: The complicating factor here, of course, over these past two-plus years, what have been some of the challenges in doing this in the time of a pandemic?

ZMUIDZINAS: Probably the biggest challenge for us was Palomar operations, trying to keep the staff safe. We shut down right at the beginning of the pandemic. I had taken the decision to shut down the observatory slightly before campus decided that they needed to take action as well. It was pretty clear to us that we simply couldn't keep operating, both because of concerns for the safety of the staff, but also because of the anxiety and apprehension amongst the staff, which was reaching a critical level. You just can't have that when you're trying to operate an observatory because mistakes can be very costly. [Laugh] You really need everybody to be able to focus on their work and not anything else. We decided we needed to shut down and have a cooling-off period until we figured out how to operate safely, lower the anxiety level amongst the staff, just talk and think it through. It took us a little while to come back into action, but we did. What we ended up doing was to reduce the number of nights we were operating the 200-inch Telescope at Palomar. Instead of seven nights a week, we went down to four nights a week.

We did that because we were concerned that if you had a staff member that was, say, working in a fairly small, fairly poorly ventilated room, and that person got sick, then you immediately had someone else come into that room, there would be a risk of transmission. It was early days in the pandemic, we didn't have a good way to judge the risk, so we decided we needed a cooling-off period in between. We would have one staff member work and occupy that room, then when their shift was over, we would take a breather and a break, have a cooling-off period over a few days, then let somebody else come in and do the next shift. We found various workarounds. The instrument complement on the telescope isn't static. We put instruments on, take them off, largely depending on the phase of the moon. When it's dark, when you have no moon in the sky, you focus on visible-wavelength astronomy because the sky's dark. When you have a full moon, and the sky's bright, you focus on infrared astronomy because the infrared is less affected by that. There's a switching between visible and infrared instruments that happens every two weeks or so, and that activity requires staff working in close quarters often.

You might need two people to do some particular activity to take an instrument on or off. We had to find ways of being able to do that kind of thing safely using some combination of choreographing their movements, where they're going to be standing, how close they're going to get, how long they'll be close, and then protective equipment, making sure they had the right gear. Those were some of the challenges in keeping going. But once we started operating again, we were able to keep operating again and gradually expand the number of nights and the range of different kinds of instruments we were able to support until probably in the fall of 2020. We were pretty much back to supporting all the instruments with maybe one or two minor exceptions. The way we handled it was not to try to go fast, but to be really deliberate about what we were doing. The key person in all of this was our site supervisor at Palomar, Rick Burruss, who did a magnificent job in getting us through the pandemic.

ZIERLER: In your capacity as director, what interface do you have at the federal level?

ZMUIDZINAS: My capacity as director, I'd say the federal interfaces that come with just that job title are reasonably minimal. Where does that happen? It happens, first of all, on the CARA board because we have NASA representatives on it, because NASA is a partner on Keck, and has a share of Keck time, and helps financially support the observatory. I see NASA colleagues at the CARA board meetings. For the TMT project, before the decadal survey, we would have interactions with colleagues, particularly from the National Science Foundation. There was a blackout period during the time the survey was happening, where NSF told us, "We simply can't talk to you during this time. It's too sensitive." After the survey was released, we started to engage with them again. Those are really the places where I have some connection.

ZIERLER: In subsequent discussions, we'll talk in detail, of course, of all your work at JPL, but at this juncture, I'm curious if you could reflect on some of the magic that is the relationship between JPL and Caltech and the science that happens only because of this unique relationship.

ZMUIDZINAS: Obviously, I could think about that and probably keep talking for quite a while. [Laugh] But I'll tell you a couple of things about how that relationship has affected me personally. The first little vignette I'll tell you is when I was an undergraduate at Caltech in the late 1970s. Like many undergraduates, I was looking for a summer job where I could work on campus and learn a little bit more about science. I landed in a research group run by Ed Stone and Robbie Vogt. This was in the summer after my freshman year, which would've been June 1978. The year before, in August 1977, the two Voyager spacecraft were launched, and Ed, of course, ended up being project scientist. But Ed and Robbie also had a cosmic ray instrument on each of the two Voyagers. When I joined the group, there was a lot of Voyager activity going on in the group. It wasn't the first thing I did, but I eventually fell into Voyager-related activities. I think it was the second summer, 1979, I was happily working in that group. The Voyager 2 encounter with Jupiter was happening, so I was sent to JPL as an undergrad to help with the encounter. In those days, all you had to do was flash your student ID card, and the guards would wave you in.

You could just go happily and walk around. Of course, there were all kinds of news vans, TV reporters, lots of hustle and bustle, people milling around. Everybody was so excited, and so was I. I was told to report to some building, so I did, then somebody walked me down the hallways and took me to an office. I had a desk, and I had this giant stack of old-fashioned fan-fold paper from a computer printer with sprocket holes on the side, a ruler, some pencils, a calculator, stuff on the desk. I thought, "Wow, this is going to be great. What do I do?" I said, "What would you like me to do?" I was really excited. The answer was, "Look busy." [Laugh] Because they had reporters walking in the hallways. I was just an extra. [Laugh] That was fun simply because I got to experience what it was like to see the excitement. It was a little bit of a letdown that I wasn't taking data hot off the DSN and plotting it or something like that. But that was fun. Being in that group, I learned an awful lot.

My mentor ended up being a graduate student by the name of Neil Gehrels, who was Ed Stone's student. His thesis related to the Voyager encounter with Jupiter, and they discovered a surprisingly large population of energetic sulfur and oxygen ions when Voyager made its closest approach to Jupiter. That ended up being his thesis, trying to understand where that came from. I think, eventually, it was understood that it had to do with the volcanoes on Io. I got to watch him go through his thesis, and observe him, and learn from him. He's a Caltech distinguished alum. He passed away a few years ago. He went to NASA Goddard after Caltech and became one of their leaders in space astrophysics. There's a space observatory named after him, the Neil Gehrels Swift Observatory. He served as principal investigator for that mission. As an undergraduate, the possibility of working in a group like that, having that connection, being able to learn from people like Ed Stone, Robbie Vogt, Neil Gehrels, I probably didn't appreciate it as much as I should've at the time. But looking back, it's just remarkable to me to think about what that JPL-Caltech connection was able to give to me as a lowly undergraduate. This is one example.

ZIERLER: How do you see in historical perspective the idea that there's JPL and campus? In other words, it's one big community, and it's not that there's Caltech, and there's JPL, which feeds the perception that somehow, they're separate organizations.

ZMUIDZINAS: In 2013, I was invited to go to a conference in Shanghai on superconductivity and to give a talk there. I came a day early to make sure I was able to get over the jet lag. I was assigned a tour guide to entertain me that extra day. It was this young guy who had just finished his post-doc at Cornell and had returned to China. He was starting as an assistant professor there. A young scientist whose job it was to keep me entertained for the day. We got in a taxi, and he was going to take me somewhere. We just started talking, and I was curious, so I asked him what people in China thought about science. "Are there any scientists that a random person on the street in China might know about, someone who's famous enough that they might've heard of them?" He said, "There's this guy in agriculture most people would probably know, and then there's this rocket guy from California." I got interested. That, of course, was Xuesen Qian. We changed our plans.

Instead of going where he was going to take me, we ended up going to visit the museum in Shanghai that was built in Xuesen Qian's honor, a big museum. He's a national hero. You walk into this museum, there's a giant rocket going up multiple stories, and you see all kinds of exhibits about what a great communist Xuesen Qian was, what a hero he was to the people, what a patriot he was. Then, you go down this one hallway, and it's all photos of Altadena and Pasadena from the time he was a student and later a professor at Caltech. Of course, he was the number-three person in the founding of JPL. Then, he got chased out during the McCarthy years by the FBI because he was accused of being a communist in the 1950s. Tragic story, but if you think back to the very beginning of JPL, it was Caltech. It was, and it wasn't. There was Jack Parsons, who was a kid off the street in Pasadena who had no connection to Caltech, he just had the gumption to walk into von Kármán's office one day, and that's how the whole thing got started. That connection goes back a long way, and JPL really didn't become JPL until NASA became NASA. JPL became part of NASA and decided to focus on exploring the planets. They decided not to get involved in the astronauts to the moon program, which was, I think, a very good decision for JPL.

ZIERLER: I want to move onto nomenclature at a very fundamental level. For you, scientifically, intellectually, administratively, there's astrophysics, astronomy, and cosmology. Where are there meaningful distinctions between these words, and where are they just simply words, and the science is the science?

ZMUIDZINAS: They're not synonymous, but there's obviously a lot of overlap. You could say astronomy is the oldest. I'd have to be careful about that because cosmology can also be thought of as being very old. But astronomy, the study of the heavens, and the study of the motions of the objects in the heavens, is a very old subject. You don't need to know any physics to do astronomy, you can simply observe the sky, and take notes and measurements, and you're doing astronomy, but you're not doing astrophysics. Then, because you've maybe done some laboratory physics and started to learn about nuclear reactions and things like that, you can start to unravel how stars actually work and what makes them shine, the physical processes in the interior of a star. Now, you're entering the realm of astrophysics. You can use astronomical measurements, make observations of the stars, particularly, look at their spectra, and try to unravel what the spectra are telling you about how the star actually works inside. And that's a long and ongoing story.

But now, you're also doing astrophysics because you are trying to apply the laws of physics to how astronomical objects behave and evolve. You're trying to understand how astronomical objects work, in a sense. That would be astrophysics. Cosmology is the study of the universe itself. In cosmology, you're not thinking about individual objects, stars, or galaxies, you're thinking about the entirety of the universe and trying to understand as much as you can about the universe itself. Some of the most basic questions you can ask have to do with the geometry of the universe. The fact that the universe is expanding was a huge discovery made on Mount Wilson, but what more can we say about that? Can we chart the history of the expansion of the universe? When you get to those questions, the questions that relate to the universe as a whole, then you're in the realm of cosmology. Of course, you use tools from astronomy and astrophysics to do cosmology. A good example of that is to use supernovae, exploding stars, as a way of probing the expansion history of the universe. You use supernovae as a so-called standard candle, an object that you know how bright it should be, but then when you observe it to be a particular brightness, because you know how bright it should be, you can gauge how far away it is, get a distance measurement. It's that kind of thing that gives you a connection between cosmology, astronomy, and astrophysics. And there are lots of examples like that. There's a lot of blending and back and forth between the fields, but hopefully that gives an idea of what the terms mean.

ZIERLER: Your educational trajectory, of course, is in physics, and you've spent so much of your research career in astronomy. Was there a grand plan there all along? Was that always your intention?

ZMUIDZINAS: No. I've never taken a course in astronomy. [Laugh] I kind of fell into it. After finishing Caltech and having a lot of fun working in Ed Stone's group, I thought, "I'd like to try something else as a graduate student." But I wasn't sure exactly what. I ended up going to Berkeley, and I thought maybe I would do theoretical physics. It didn't take me long to figure out that was probably not what I should do. I was assigned as a teaching assistant in a course for freshman, loads and loads of students, and the senior teaching assistant that was shepherding all the other teaching assistants was a fifth- or sixth-year graduate student in theoretical physics who had yet to find a research advisor for his thesis. Once I met him, I realized, "I'll figure out something else to do. [Laugh] This doesn't look like a good path." That was the time of the early Reagan years, and there was a recession going on in the economy. People were graduating with their PhDs in physics and struggling to find jobs. I figured whatever I did, I'd better learn at least a few practical things so that when I graduated, I could find employment.

I started looking around for an experimental project to do, a project where I would learn lots of different things, something that wouldn't be too exotic, something that would give me a practical background. I ended up in experimental astrophysics, and the project I ended up in was to start working in this area of far-infrared astronomy. Submillimeter astronomy is another term you'll hear, but they're more or less the same thing, wavelengths shorter than a millimeter. The project I worked on was an instrument, and it was going to use a laser, so I was going to learn about lasers, it had a detector that needed to get cold, so I was going to learn about cryogenics and vacuum systems, and it had a lot of electronics behind the detector, so I was going to learn about microwave and regular electronics, and the data needed to go through a computer, so I was going to learn about all that. It just seemed like a perfect project where it was going to be a little bit of everything. Optics, you name it. I figured I would almost certainly learn something I could translate to employment later on doing that. That's how I fell into astrophysics. I was trying to be practical. [Laugh]

ZIERLER: At a more specific level, the kinds of astronomy you do, there's optical, infrared, submillimeter, is there a particular methodology that's closest to your heart, the thing that's most important to you for the research questions you've posed over your career?

ZMUIDZINAS: Because I come at this as a physicist, I've got a very deep interest in how you actually perform the measurements, how to get your equipment working at levels of performance that reach the fundamental limits set by physics. In other words, how to make the instrument the best it could possibly be, and what science does that enable when you do that? My interest has been very much looking for opportunities to improve the state of the art, to be able to enable measurements that couldn't have been made before because you have a new way of doing things, some new technology or method for measurement, then trying to marry that with interesting scientific problems and finding that intersection, that sweet spot, where you can make an important scientific advance because you're making an important technical advance. That's been my MO over the years.

ZIERLER: How close does that get you, even unofficially, into actual engineering, instrument-building, understanding how these things work?

ZMUIDZINAS: As a graduate student, I think one of the first tasks I was assigned was to go polish some mirrors we were going to use on a laser. That meant actually taking a mirror, and putting it on a grinding wheel and polishing wheel, and learning how to become a very bad optician. [Laugh] But nonetheless, maybe the first half-rung on the learning curve of what it takes to become a master optician. Then, I was put to work designing microwave amplifiers, so that meant figuring out the circuit design, doing circuit simulations, getting all the parts and assembling it under a microscope by hand, soldering things together, cooling it down, testing it, etc., and having that be the thing that ends up getting used in the instrument, to doing a lot of mechanical design for the frame that held our instrument on the airborne telescope we were flying on. We were flying a laser, and the laser was very finicky. It couldn't tolerate a lot of jostling around or bending, so the frame had to be very stiff.

I had to learn mechanical engineering out of the book, treating it like another physics problem. It's been a lot like that, learning just enough about any particular subject, whether it's mechanical engineering, electronics, optics, or so on, to be able to come up with an effective design that makes the instrument work. I did get an extremely broad exposure as a grad student to all kinds of fields of engineering and physics. Over the course of a career, as you get more and more senior, you find more efficient ways of doing things. As a grad student, your time is nearly free, so it doesn't matter if you're efficient. [Laugh] It's OK to be spending your time on that. But when you're a professor, maybe not. Maybe you need to hire a professional engineer, a professional electronics technician, because your time becomes more valuable.

ZIERLER: In light of all the data, are you involved in the broader effort to have both the computational and human brainpower to make sense of it all?

ZMUIDZINAS: I'd say that's certainly an area I don't get involved in in any serious way. Over the years, I've certainly done a lot of data analysis myself, written a lot of software for both acquiring and analyzing data, doing physical modeling to understand what the data mean. But that part of my career is over. It's been over for a while. These days, I don't spend a lot of time with hands-on data analysis. That field as a whole has continued to move. It's becoming more and more sophisticated. For instance, at Palomar, there's the Zwicky Transient Facility project scanning the sky, looking for interesting transient phenomena. The rate at which data are collected in that project is just enormous, and sorting out the wheat from the chaff, the interesting stuff from the been-there, done-that stuff, is a real challenge. They're applying some interesting techniques, so-called machine learning techniques. Not quite fair to call it artificial intelligence, although some people do. Those kinds of techniques are used in astronomy. I'm just not the person doing it. Had I been 10 or 20 years younger, I'd probably be doing it. I'm just not at that phase of my career anymore. [Laugh]

ZIERLER: What have been some of the real game-changers in technology, quantum leaps, if you will, that have allowed the field to progress in ways that simply were not possible otherwise?

ZMUIDZINAS: I gave a plenary presentation to the SPIE, Astronomical Telescopes and Instruments Conference. This is the large conference every two years in that field. Typically, a few thousand people attend. This was virtual, of course, because it was the middle of the pandemic. But that was my topic, technology in astronomy. In that talk, I chose to highlight three different things because I was looking for a way to weave the topics together, and we just had the Nobel Prize to Andrea Ghez and Reinhard Genzel for their work on the black hole at the center of the Milky Way. Then, a few years before that, there was the Nobel Prize for LIGO, for Kip Thorne, Barry Barish, and Rai Weiss. Then, in 2019, we had this so-called image of the black hole from the Event Horizon Telescope, which Katie Bouman, who's on the faculty here, was involved in. I thought, "Let's make this talk about black holes, and let's talk about some of the technologies that allowed those discoveries to happen."

The organizing theme was black holes, and it gave me license to talk about all kinds of interesting technologies. I spent some time talking about LIGO technology, and that's a fascinating subject. LIGO really is a 40-year effort in technology development, just a heroic story in technology development. When I was a senior at Caltech, I took a course in general relativity, which was being taught by Richard Feynman. I was still a lowly undergraduate, a senior. There were lots of grad students in the course, and professors who would come listen to the lectures because it was Feynman. Stephen Hawking would roll up in his wheelchair at the back of the class when he was in town. I was this lowly undergrad completely overwhelmed by the scene. [Laugh] Throughout most of the year, the seats in front of me were occupied by two professors. It was Stan Whitcomb and Ron Drever. They were hired to start this gravitational wave program, and they figured it was a good time to brush up on gravitational waves and general relativity.

We eventually got to the topic of gravitational waves, and we were going through the math and physics of that. Feynman handed out this letter he had written in the early 1960s, a letter he sent to another famous physicist, Viki Weisskopf at MIT. It was at a time when Feynman was trying to bring quantum mechanics and general relativity together, which is still an outstanding problem in physics. Nobody knows how to do that. But Feynman was working on this problem, and he wrote this letter to Viki Weisskopf explaining what he'd been doing and how far he'd gotten. Towards the end of this letter, he starts talking about whether potentially we might be able to see gravitational waves experimentally. Towards the end of this letter, he says, "I've not seen proposals for such experiments, except by crackpots." We had the two crackpots sitting in the room in front of us. [Laugh] And we knew they were crackpots because we'd been through the math. We saw the numbers. We knew how horrendously hard this was going to be. It was amazing to think that these two people sitting in our classroom were actually going to try to do this because of how hard it was going to be, and yet they did it. It was just an absolutely heroic story that LIGO got pulled off. But that's another story in technology.

Then, in terms of the Reinhard Genzel and Andrea Ghez story, on a personal note, Andrea was maybe a third-year graduate student at Caltech when I started as an assistant professor. She was on my floor working with Gerry Neugebauer and Tom Soifer, so I'd see her a lot in those early years. Reinhard Genzel was my faculty research advisor at Berkeley, so I knew him pretty well. It was interesting to see them win for that. But that was a story of, you could say, adaptive optics at the Keck Observatory for Andrea's case. And also infrared cameras, such as the NIRC and NIRC2 cameras that Keith Matthews and Tom Soifer built for Keck. In Reinhard's case, it's the European telescopes, including the VLT, but again adaptive optics and infrared cameras. But the radio image of the black hole, the Katie Bouman image, the primary technology that made that work was invented by Tom Phillips, who's retired from Caltech. He came to Caltech in 1978 or '79, when I was an undergraduate, and he joined the faculty. He came from Bell Labs, and he also stumbled into astrophysics. He was a low-temperature physicist, and there were these two famous people at Bell Labs, Arno Penzias and Bob Wilson, who had discovered the cosmic microwave background in 1965, basically by accident, but it was a big discovery, and they won the Nobel Prize for it.

But in the late 60s, they were working on something else, millimeter-wave astronomy, and had detected the carbon monoxide molecule for the first time in interstellar clouds. And that also turned out to be a rather major discovery for astronomy. Arno was apparently giving a lecture about this at Bell Labs and was talking about the receiver they built to make this discovery, talking about the sensitivity of the receiver. Radio receivers have a sensitivity measured in temperature units, of all things. You talk about the noise temperature receiver, how many Kelvin, that's the unit that's used. Penzias's receiver had a noise temperature that was thousands of Kelvin. After the talk, Tom Phillips was talking to Arno, and he said, "Why's your noise so high? Why isn't it at least room temperature, say, 300 Kelvin? And why don't you cool it so it could be a lot lower, like 10 Kelvin?" I guess Arno got mad at Tom and said, "If you think you can do better, why don't you?" And I guess Tom took that as a challenge, and that's how he became a radio astronomer. The first thing he did was to build a receiver that was a lot better. Then, he went on to pioneer millimeter and submillimeter astronomy with his receiver that was a lot better, in the early to mid-70s.

But it wasn't perfect. It had its limitations, so he was looking for something better. At the time, IBM especially, but other companies like Bell Labs, had rather large programs in trying to develop superconducting computers. The idea was that, "Eventually, silicon is going to run out of steam, and we'll need something better. Let's try making a computer using superconductors." They had big programs studying this. What that meant was that they had people working in labs, making superconducting devices, especially so-called tunnel junctions, a key device that you need. Tom saw this work going on and realized these tunnel junctions being made could potentially also be used in instruments, in radio receivers for millimeter and submillimeter wavelengths. He started experiments to try to use them. It took a while, but by 1978, he had gotten the thing working in the lab for the first time and was seeing that it was actually going to work. These were the so-called SIS superconductor receivers. That's presumably at least one of the reasons why Caltech hired him to come to the faculty, that invention, among other things. That invention completely transformed millimeter and submillimeter astronomy.

It ended up being the way that everyone builds receivers at those wavelengths. That particular device, if you design and build it carefully, can reach the limits of sensitivity that are set only by quantum mechanics, the Heisenberg uncertainty principle. You get to this limit that physics says you just can't get better than, which is really amazing. And that technology is what makes ALMA work. ALMA is the largest single investment in ground-based astronomy today. It was built for the cost of, like, $1.5 billion. It's this big millimeter and submillimeter interferometer in Chile at 15,000 feet altitude. It has 60-plus telescopes. Each telescope is a 12-meter dish equipped with these superconducting receivers. It's ALMA fundamentally, and this enormous sensitivity that ALMA gets because of these superconducting receivers, that made the Event Horizon Telescope image of this black hole possible. The raw sensitivity of ALMA enabled that image. And all the other telescopes they used to make that black hole image, telescopes located at places scattered around the earth, whether it's at the South Pole, in Hawaii, or somewhere else, all of those telescopes are using the same superconducting receivers. If I had to name one technology that made that black hole image possible, it's Tom's invention of the superconducting SIS receiver. ZIERLER: In the way that you explained your happenstance entry into astronomy and astrophysics after your education in physics, your research career as an experimentalist, does that go back to your education? Were you also focused on experimentation as an undergraduate and graduate student? ZMUIDZINAS: As an undergrad, I had a vague idea that I might want to do experimental physics. But I was also maybe thinking I might try to do theoretical physics, I wasn't sure. The work I did in Ed Stone and Robbie Vogt's group was really experimental work, but I wasn't in the lab, I was dealing with data. The biggest project I worked on while I was there was the calibration of the electron telescope that flew on Voyager. And that was a lot of data analysis, trying to characterize how the instrument performed and taking data that had already been collected, stored on big computer tapes, writing computer programs to crunch through the data and calculate the instrument characteristics. That was something that was kind of neither experiment nor theory. Probably a little more experiment, but a lot of analytical work and computer programming. I hadn't gotten solidly into experimental physics yet, except through the experimental lab courses I was taking, which dipped your toe in experimental physics. It wasn't until I got to Berkeley that I really got introduced to experimental physics in a serious way. It was a great training for me because I got to do lots of different things and learned just enough about everything to take me for the rest of my career. ZIERLER: Given your interest in technology and its impact on the field, I wonder if you're involved at all in the broader effort at Caltech in quantum science, some of the excitement that quantum information, even quantum computers, might have long term in astronomy. ZMUIDZINAS: The first thing I'll say about all that before answering your question is that in our freshman class, everybody knew who the smartest kid was, and that was Peter Shor. [Laugh] ZIERLER: Say no more. [Laugh] ZMUIDZINAS: Peter Shor was my classmate, and he was a lot of fun. He introduced me to the Rubik's cube. I saw him doing it sitting in the corner at Ruddock House when it was still called that. I asked him, "What's that thing you're playing with?" He kind of showed me and did a couple moves. I said, "How do you do it?" and he said, "Think about it." [Laugh] So I did, and I learned how to do it. It was a lot of fun. ZIERLER: The origins of Shor's algorithm right there! [Laugh] ZMUIDZINAS: Everybody knew that Peter was the smartest kid in the class, and that turned out to be true. Moving forward, one thing that's kept me busy over the past 20 years or so has been working on a new type of superconducting detector that I invented along with Rick LeDuc, my longtime colleague from JPL, probably the person at JPL I've worked closest with over the longest number of years. We had this glimmer of an idea in 1999, and we started working on it. It was a really simple idea. And that was, with a very simple fabrication procedure, how do you make a superconducting micro-resonator? You basically take a superconducting film, you pattern it using the tools of lithography, the same kinds of tools used to make computer chips, and the pattern becomes something that rings like a bell at microwave frequencies. It has a very specific resonance frequency at which it likes to ring in the microwave range. If you shine millimeter and submillimeter radiation on it, the frequency it rings at can shift slightly. By listening to it ring, you can detect the radiation landing on it. It's a really simple idea, and because it's a simple idea, you can get it to work. Also, you can make lots and lots of them, and each one of them can have a slightly different resonance frequency, which means you can have a whole array of these detectors working simultaneously and measure the radiation landing on any one of them independently. Essentially, you can make an imaging array of detectors this way using a fairly simple fabrication procedure. At the same time, it can be extremely sensitive. This is the kind of technology that is being baselined for this$1.5-billion far-infrared probe that NASA might be pursuing over the coming decade. But back then, we were just starting to work on this idea, and the first thing we needed to do was to see if we could make these little resonators and how well they worked. It turned out, nobody had actually explored this possibility, at least using the kinds of materials and at the rather low temperatures we were going to be looking at. For whatever reason, there just hadn't been a lot of work done in that area. We didn't have much to go on other than what we could predict from theory. Of course, you make those predictions, and what the theory tells you is that it's not going to work any better than this.

But what theory doesn't tell you are all the other problems that creep in that you don't know about because you haven't run into them, and it might be a lot worse because those are the things you haven't learned about yet. We needed to start testing these devices. It took a few years to kind of really get dialed in, but after a while, we started to make devices that were really quite good, that had rather good properties and were good resonators. A former student of ours by the name of Rob Schoelkopf came to visit and saw what we were doing with these resonators, and he had an idea about how this might be applied to some of the things he was thinking about that related to quantum devices. A year after that, in 2004, he published a paper, which has now become the most or second-most cited paper ever published with the word superconducting in its title. It's become an extremely well-cited paper. What Rob basically showed was how you make a superconducting quantum bit, a qubit, using these resonators, that has good properties, or properties that are good enough that you can start to think about using it as the basis of a quantum computer.

Rob, today, has a well-financed startup company trying to develop quantum computers. If you've heard of the work that Google is doing in their quantum computers, they're using a very similar approach with superconducting resonators. IBM, the same thing. Lots of groups and startups around the world. These superconducting resonators have proliferated everywhere, and the quantum world has taken over this concept and applied it to many different applications in that area. It's actually been extremely beneficial for us because the kinds of problems and issues that are important for the quantum community have helped us understand some of the issues we were dealing with on the detector side. The fact that there's this much larger community of people studying these devices, learning about them, finding out the funny ways they can go wrong, has turned out to be a real help on the detector side. That's an interesting connection. I personally have never really gotten involved in this quantum information science area. I've had my hands full doing other things. But I certainly have a lot of contacts and friends in that world. Another device that we've worked on that also connects us to that area, it was something that we invented in 2010.

We were playing with various kinds of superconducting materials for use in detectors. We started off with simple ones, elemental superconductors like aluminum, for instance, a pretty simple metal. But eventually, for various reasons, we got interested in whether we could use some more complicated materials. One set of materials we looked at were nitrides. Titanium nitride is an example. If you go to Home Depot, and you buy a drill bit, and it's a shiny gold color, it's because it's got a titanium nitride coating on it. It's an extremely hard material. That's why it's put on drill bits. But it also turns out it's a superconductor that superconducts at about 4.5 Kelvin. If you play tricks with how much nitrogen is in there, you can change the temperature it superconducts at, you can vary it over a pretty broad range. That was of interest to us for detectors. We started studying that material. And other flavors. There's niobium titanium nitride, basically a cousin, where you mix in different amounts of niobium and titanium, not just pure titanium nitride. What we learned in studying detectors made from these materials, studying these micro-resonators, was that these nitride superconductors had rather phenomenal properties we hadn't seen before in the regular superconducting materials like aluminum.

Specifically, the property that we used, the idea that this resonance frequency shifts when you shine light on the device, has to do with one of the electrical properties of a superconductor, a property called the kinetic inductance. It sounds kind of complicated, but it basically just has to do with the fact that in the superconductor, instead of single electrons, you have pairs of electrons moving to carry the electrical current, and the pairs of electrons basically move back and forth without any friction. That's why the material's a superconductor. They just go back and forth, and there's no friction. And they're accelerated by the electric field. They speed up, and as they're accelerated, their kinetic energy goes up. Then, they slow down because the electric field reverses direction, and it slows them down. They're just moving back and forth, oscillating back and forth, and their kinetic energy is going up and down, up and down. There's energy sloshing from the electromagnetic field into the motion of these electron pairs, then coming back out into the electromagnetic field. This sloshing of energy between the material and the electromagnetic field is known as the kinetic inductance.

That's the basic property that we use to make these detectors work, this kinetic inductance effect and the fact that this kinetic inductance changes when you shine light on the superconductor, that change in the kinetic inductance is what causes the resonance frequency to shift. One of the interesting things we discovered with these nitride superconductors is that this kinetic inductance had some interesting nonlinear properties. What that means is that as you crank up the microwave field higher and higher so those electrons are sloshing more and more, the kinetic inductance property started to change. It wasn't the same. When you had a small tickle of a microwave field, you had a certain kinetic inductance. When you had a large tickle, the kinetic inductance went up and by a lot. This is a very interesting property for a physicist, the idea that you have this inductance characteristic which is nonlinear. It turns out that this provides a physical mechanism for being able to construct extremely low-noise so-called parametric amplifiers, which have been known since the very early days of telephony. They used to make amplifiers this way using magnetic materials, then eventually they figured out tubes and threw all that stuff away, then figured out transistors and threw all the tubes away.

But there was a spurt in the 1950s at the dawn of the space age when radio astronomy was getting going, radar had gotten started in World War II, communication from space was becoming a thing, and people needed a way of making low-noise microwave receivers to receive these signals from space. And they needed a way to make low-noise amplifiers. They started using the same class of device, parametric amplifiers, that used semiconductor diodes as the key element. There was a lot of work on this kind of amplifier in the 1950s. By early 1960s, it was understood that this kind of amplifier could, in fact, operate at the fundamental limits set by quantum mechanics, the Heisenberg uncertainty principle. There's a very famous paper coming from Bell Labs in 1963, something like that. One of the authors on that paper is Amnon Yariv, from applied physics at Caltech. It's a very famous paper. That was the paper, I'd say, where, first of all, they showed that this class of device, parametric amplifiers, could achieve a sensitivity, a noise performance, that was set only by quantum mechanics and really provided a solid theoretical analysis of that.

Even before then, people had understood that there should be this quantum mechanical limit to amplification. But if you go back and look at those earlier papers, the arguments weren't quite rigorous. They break down. They weren't quite correct. One of the early papers was written by Charles Townes, a Nobel Prize-winner for the laser invention, a longtime Caltech trustee. Essentially, my academic grandfather at Berkeley. He was one of the people to very early figure out that there was this quantum mechanical limit to amplification. Much later, in the early 80s, because of LIGO, Carlton Caves, who was a grad student with Kip Thorne, wrote a really masterful paper about this whole topic, which is now the key reference everybody goes to to understand this. But he had the benefit of a lot of earlier work. Not to take anything away from Caves's paper, it's still a masterwork, but there was work before. We knew about this parametric amplifier, we saw these nitride superconductors had just the right kind of magic properties to make them work, and we realized that we could do something with this combination that had never been done before using superconductors, and that was to make an amplifier which was simultaneously, one, very low-noise, operating at the fundamental limits of physics set by quantum mechanics, and two, very broadband, it could operate over a wide frequency range.

When we could do that by taking advantage of some work that dated back to the later 50s and early 60s, on so-called traveling-wave parametric amplifiers. And three, because of the properties of these superconductors, the amplifier would be capable of not just being very low noise, but also could deal with relatively strong signals, so the so-called dynamic range would be very high. The ratio between the largest signal the amplifier can process versus the smallest signal it can process, set by the noise floor, that range is called the dynamic range. If you're making measurements, it's extremely useful to have a very wide dynamic range so your instrument can tolerate all kinds of signals. That was work that we did. We published a paper in 2012, and Peter Day (JPL) and I submitted a patent application in 2010 or so. Peter has kept pushing on this, in recent years with graduate student Nikita Klimovich, and that work's been progressing very well. It hasn't yet made an impact on astronomy, although it may revolutionize ALMA in 10- or 20-years' time. But it's also having an impact in the quantum arena. They also need very low-noise amplifiers for their devices, and there's starting to be some crossover in that area. There are connections between these fields. We're all in the business of trying to make sensitive measurements. The tools you use, not surprisingly, end up being fairly common, including superconductivity and low temperatures. That's what gives us that contact.

ZIERLER: You mentioned theory. What have been, over the course of your career, some of the anchor theories that have served as guideposts for your work?

ZMUIDZINAS: Obviously, in superconductivity, there's the very famous theory of superconductivity, Bardeen-Cooper-Schrieffer, BCS, from 1957. I'd say if you forced me to give one answer, that would be it. The good old BCS theory of conventional superconductors, nothing fancy, has been our workhorse. For every single kind of superconducting device I've been involved in, that's what we've needed, BCS. The fundamental theory is BCS, but its implications had to be worked out in many other papers, so there are many related papers. But that's the key theory on that side of things. In astrophysics and astronomy, it is, of course harder to really name one key theory. Really, you could say astrophysics is applied physics. You take the physical laws you know about, usually from experiments on earth, whether it would be electromagnetism, gravity, nuclear physics, particle physics, or whatever. You use what you know about physics from those experiments, and you apply it to the astrophysical setting. Different astronomical objects involve different physics. It's hard to point to one single theory and say it's the key thing because there's a lot involved, and it changes depending on what the topic is in astrophysics. Of course, in cosmology, there's really only one theory that matters, which is general relativity, Einstein's theory of gravity.

ZIERLER: Last question for today, as much a time-management as a scientific question. With all of your administrative responsibilities, how have you managed to stay close to the science after all these years?

ZMUIDZINAS: I'd say it certainly gets harder with time. My style of working has been shifting over the years. When I came to Caltech as an assistant professor, it was me and a lab that was full of junk that other people didn't want. [Laugh] That lab had become the place where people dropped off their junk. My job was to get rid of all the junk and turn it into a functioning lab, which meant doing everything myself. Ordering the lab benches, ordering the equipment, setting it up, building the cryostats, building the electronics, getting the operating systems installed on the computers. I did everything. I was a one-person show for at least the first six to nine months as an assistant professor until I gradually started expanding the group. But over the years, through the first ten years, being on the faculty, I was still pretty much in that mode where I had my fingers really deep into everything.

When I went to the telescope to go observing, I'd run around the observatory with wrenches sticking out of my pocket, pulling out the oscilloscope, taking a piece of equipment off and opening up the lid because it wasn't working right, figuring out what was wrong. I was very much an experimentalist running around an observatory, trying to get instruments to work correctly, to work at their limits. I'd say the turning point in my life came in 2004, 2005, when I had been suffering from colitis, and I was on these fairly weak immunosuppressants that stopped working for whatever reason. And nothing else after that worked. The only solution was surgery to have my colon removed. That was basically late December 2004, then my recovery was in the beginning of 2005. I was no longer in the lab, I needed to pull away from work and recuperate. It took me a good nine months to recover and be able to start going back into work. That's really when the style of work for me shifted. I was forced to delegate a lot more than I had. When I came back, I realized delegating's OK. [Laugh]

ZIERLER: It's a hard lesson learned.

ZMUIDZINAS: And then, life just kind of took off from there. In 2007, I was asked to serve as director of the Microdevices Lab, which meant spending a fair amount of time at JPL and dealing with that. Which, again, left me with less time for hands-on work. Then, when I became Chief Technologist in 2011, that really pulled me away from campus. I really had not that much time, and I really needed to rely on other people. I mentioned a few of them. Matt Bradford is one of them. He was my post-doc circa 2000, and he stayed on at JPL. We maintained a close connection. Starting around the time I became chief technologist, he started taking over some of the projects I had initiated in superconducting detectors, and my colleagues at JPL have kept things moving forward. I was able to remain involved at the level of supervising students or post-docs, contributing to proposals and so on, but these days, I'm really relying on other people to keep that work going forward.

ZIERLER: This has been a terrific conversation. I look forward to subsequent discussions. Next time, we'll go all the way back to the beginning and develop your personal narrative.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Monday, March 14, 2022. I'm delighted to be back with Professor Jonas Zmuidzinas. Jonas, it's great to be with you again. Thank you for joining me.

ZMUIDZINAS: Likewise. Good to be with you, David.

ZIERLER: Our first conversation was a great tour of your overall approach to the science, research, and administration. Today, I'd like to go all the way back to the beginning and develop your personal narrative. But first, a question we're all dealing with right now, for you, with your particular research expertise, the war in Ukraine. Are you seeing, at this point, fallout in the broader astronomy world or at the interface of space exploration and defense research? Have those issues already started to crop up, from what you can see?

ZMUIDZINAS: Certainly, it's been a hot topic of discussion. Amongst the faculty, there have been emails circulating. I'd say personally, I don't have any collaborations that intersect with Ukraine, although some of my colleagues do. There have been impacts resulting from that, collaborations that have basically been put on hold. And I've been reading. I try to read as much as I can about what's happening. There have been a number of articles, especially what's happening in space, and more recently, there was an article about CERN and CERN issuing a statement, different scientists in the US finding themselves perhaps with somewhat different viewpoints about what the right thing to do is, echoing a lot of the discussion I saw with the emails circulating amongst the faculty. Basically, what do you do? If you have a collaboration, and you stop it, that's going to impact your collaborators in Russia, obviously. Now, you could say they should speak out against Putin and the war. Of course, right now, the conditions for doing that are not so good. You might easily get arrested for speaking up.

The other argument I've heard is that you'd like to keep communication channels open, maintain your contacts, and at least try to learn what's happening from a different channel. That was an argument, I think, that was pretty prevalent in the Cold War days. Certainly, in the later 70s, early 80s when I started to pay attention to that kind of thing, that was the kind of argument being made. And I understand that. But at the same time, the situation today is very different. We have a country that has invaded another and is committing atrocities. It's maybe not where we were during the Cold War 1980s. Maybe the response needs to be different. In other spheres of life, in the arts or in sports, for example, we're seeing consequences. The Russian team not being allowed to participate in the World Cup. There was a conductor in Munich, Valery Gergiev, and the famous soprano, Anna Netrebko. The conductor lost his post, and the soprano is no longer invited to perform. I think fallout is inevitable. And I don't know to what extent applying pressure to the Russian scientific community is going to be effective at getting Putin to change his mind. But at the same time, getting the message to different slices of Russian society that things are not OK, I think, is important, and I think that's what's happening. I wish I could come up with a great idea for how to influence the situation, but at this point, I'm like the rest of the world, just watching in horror and hoping there's a way out of this.

ZIERLER: Specifically for the astronomy community, how well-integrated is Russian astronomy with the kinds of things you've done over the course of your career?

ZMUIDZINAS: I'd say not particularly well. In my area, in submillimeter and far-infrared astronomy, the Russians have been pushing this project they call Millimetron, which is supposed to be a fairly large, of order of ten-meter, telescope in space equipped with instrumentation that works at these long wavelengths. This has been a project that has been around for a long time, and there's some skepticism about whether it's going anywhere. But at the same time, I have close colleagues, one example is Thijs de Graauw, who was the principal investigator for what's known as HIFI, the Heterodyne Instrument for Far Infrared, that flew on the Herschel Space Observatory that I was closely involved in. My group produced some hardware for that instrument. He later became director of ALMA, which is this big array of submillimeter telescopes in Chile. As I think I mentioned last time, it's the world's largest ground-based astronomy project to date. I think he retired from ALMA, then after a little while, started working with the Russians on Millimetron, spending time there and trying to help them pull it into shape.

I don't know to what extent he's continuing to participate. I'd be interested to talk to him. My guess is that that's been cut off since this invasion. Hopefully, I'll have a chance to catch up with him at some point and see what's happening. There are other colleagues of mine, I'd say from the more device physics side, like T. M. Klapwijk, a professor at T U Delft, a quite well-known experimentalist in superconductivity who crossed over into superconducting devices for astronomy. Teun had some kind of visiting position in Moscow and would spend time there. This was maybe in the early 2010s, he came here and spent a sabbatical at Caltech in 2010. It was after that, maybe 2011 or 2012, when he started spending time in Moscow. He has close collaborations. They have a lot of good scientists in superconductivity in Russia, so those collaborations were fruitful for him. But I imagine that he also may be reassessing what to do. It hasn't reached me directly, but I'm sure I know people quite well who are affected directly.

ZIERLER: Perhaps in happier news, let's go back and develop your family narrative. How many generations back on both sides does your family go in the United States?

ZMUIDZINAS: My father was born in Lithuania, which was part of Czarist Russia until 1918, then became independent. He was born in 1930 in Lithuania. Then, of course, World War II came. My grandfather, born in 1898, was a diplomat for independent Lithuania. He studied in France in the 1920s and was stationed in London in 1932-37, but returned to Lithuania in 1938, before the war. It was dangerous for him to remain in Lithuania when the Soviets came in. They escaped and ended up in a displaced persons camp in Germany. I believe they first escaped to Austria near the end of the war, then somehow ended up at a camp in Greven, Germany. That was in the British zone, so in 1947 they were able to immigrate from there into the UK. Apparently, most of the people at that Lithuanian camp were encouraged to immigrate to the UK, for work.

ZIERLER: Was it a government in exile situation?

ZMUIDZINAS: No, not quite yet. By that point, I think the Soviets had occupied Lithuania. There was no government in exile, although Western governments did not recognize the occupation, so in 1962, Canada named my grandfather the honorary Consul General for Lithuania. My father was an only child, so it was my grandparents and my father. They left the UK and immigrated to Canada, first to Montreal. This would've been sometime in the early 1950s (in 1951). Then, my father had to go to work to help support the family. He worked at the telephone company, where he met my mother, who was working as an operator. She is French Canadian, grew up in Quebec, and has family roots that go back a number of generations. Her maiden name is Chabot, and that name is pretty widespread in Quebec. They got married a little while later. I guess at that point, life became serious for my father. He decided he needed to return to school and get an education. They left Canada and went to Indiana, to Fort Wayne. I think it was the Indiana Institute of Technology, if I remember correctly. He got a bachelor's degree in engineering after only two years and went to Caltech for graduate school. They arrived here in Pasadena in 1958, I believe. My oldest sister was born in Indiana, I believe, then they moved shortly after that. I'm one of five children, and the rest of us were born in California. I was born in Duarte, a town a few miles east of Pasadena, where my parents were living while my father was a graduate student. He finished in 1963.

ZIERLER: What was his degree in?

ZMUIDZINAS: He came as a student in electrical engineering, then decided that physics was more interesting, so he switched into physics, and he got a degree in theoretical physics. Basically, particle theory. Then, during the time that he was a PhD student, he had already started spending time at JPL and immediately moved upon graduation into a position at JPL, where he spent the rest of his career.

ZMUIDZINAS: I do. My wife reminded me, so I'll tell the story. His thesis advisor was Fred Zachariasen, and his wife Nancy passed away maybe a week ago. My wife knew her through the Caltech Women's Club. That was an interesting time to be at Caltech, in theoretical physics especially, with Feynman and Gell-Mann. My father, of course, knew them. I believe Gell-Mann suggested the topic that ended up being my father's thesis. I have a fuzzy recollection of what happened then. I have this recollection that my father was working on one problem, and ended up getting scooped because a publication came out as he was working on it, so he had to switch to a different problem, and in a rush, produce a thesis. I also have a fuzzy recollection of my father telling me that at some point, Gell-Mann's Jaguar wouldn't run, and he had to go under the hood and fix it for him. [Laugh]

ZIERLER: Being a former engineering student, I guess that's expected. [Laugh] I wonder if him getting scooped was around all of the excitement with quarks at that point.

ZMUIDZINAS: I doubt it. It's possible, but I don't remember my dad ever talking to me about the problem he was working on being quarks. I'm sure he had a lot of fun being at Caltech in that area at that time. But of course, he had a growing family. By the time he graduated, there were four children. My youngest brother was born a year or two later. It was a hectic time, I think.

ZIERLER: What was his first job at JPL?

ZMUIDZINAS: He was a theoretical physicist at JPL. This was the 1960s, when the space program was going gangbusters. From what I can tell, he was doing particle theory at JPL. He was allowed, as far as I could tell, to work on whatever he wanted. They scooped up all the scientists they could find because NASA was throwing money at the space program, and JPL figured it needed scientists. I suppose it didn't worry too much about what they did in the early years. That's what I remember. But then, I think, as the Apollo program tapered off, and the NASA budget started to contract, my father had to find ways to become a little more relevant to NASA and JPL. But he continued basically to do theoretical physics throughout most of his career, perhaps applied to problems that were of more interest to NASA. But he was pretty much a one-man show. He would write proposals for funding to work on various things, he would find collaborators, and he would fund himself. This was OK for most of his career, but I think towards the end, it got to be pretty difficult to keep that going at JPL. He ended up doing some mission work in the later years. I think he wasn't entirely satisfied with doing that work, so he ended up retiring in the 1990s. It was maybe 1994 or 1995, something like that, when he retired.

ZIERLER: Does JPL currently employ any theoretical physicists? Do they support fundamental research?

ZMUIDZINAS: JPL does support what you could call fundamental research. I think you would be hard-pressed to find a scientist at JPL that was in my father's mold. I think it has to be a lot more closely tied to missions or projects of interest to JPL. I'll give you an example. Olivier Dore is a cosmologist who is at JPL and I believe came as a result of the Planck Mission, which was a mission to study the cosmic microwave background. There were a number of people involved on the hardware side, including Andrew Lange, who was a professor and division chair in PMA up until he committed suicide in 2010, but then there were also people who had to deal with the data coming in from Planck and the interpretation of those data. Olivier, I believe, came to JPL for that purpose, to be involved in the Planck data analysis. He's a cosmologist and a theorist, and he has stayed at JPL, but JPL is involved in other cosmology missions such as Euclid, the Roman space telescope, and SPHEREx, for which Jamie Bock serves as the principal investigator. JPL and NASA missions are continuing to do cosmology, so someone like Olivier is extremely important to guide the scientific direction of those projects, and especially to guide the analysis of the data. There are people like that who have, I'd say, a fundamental science background, who would consider themselves as theorists, scientists. But they're at the intersection of theory and data.

ZIERLER: So the time of a pure theorist like your father is really a bygone era.

ZMUIDZINAS: Yeah, it would be tough to make a living at JPL without more contact with the business.

ZIERLER: Growing up, did your father involve you at all in his work? Did you have a basic idea of what it meant to be a theoretical physicist?

ZMUIDZINAS: My understanding of what it meant was that my father, after dinner, would go sit at a big desk and scribble all over piles and piles of paper, writing out long equations, and I had no idea what he was doing. He would just fill up page, after page, after page. There'd be giant stacks of pages with equations written on them. And it didn't seem particularly interesting to me, and I never really asked him much about it.

ZIERLER: Did he ever take you to JPL? Did Caltech loom large in your mind as a kid?

ZMUIDZINAS: He did take me to JPL. We had open houses. I remember visiting his office, walking around JPL. That was a lot of fun. This was probably in the early 70s. Obviously, my dad worked there, so I knew about JPL. He would bring home these glossy photos or brochures about the JPL missions, and that seemed kind of cool. I liked it. Growing up in the 60s, in the LA area, the aerospace business is big here, and a lot of my friends' dads were engineers working at companies. You'd eat your breakfast in the morning, and the box of Wheaties would have some astronaut on the back. Everybody was crazy about space back then. It just seemed normal. But it was just another thing. It wasn't, I'd say, something that I paid too much attention to. I had this idea that maybe I'd be a scientist, but it was more because that seemed like the thing to be in those days as opposed to something I was particularly interested in. I think I told you, I didn't really get interested in science until 9th grade. Before then, I was an indifferent student, mostly I was interested in riding my bike. I think I told you about this algebra teacher who made us sit according to how we were doing in the class. The element of competition got me interested. It was after that 9th grade class that I decided A, I liked math, and B, I seemed to be doing well at it. It was at that point that I started talking to my dad more about math and science. I was actually a little upset with him that he hadn't turned me on to it earlier. [Laugh] But it was OK.

ZIERLER: Did your parents communicate to each other in English?

ZMUIDZINAS: My mother learned to speak Lithuanian, so at home, especially when my father was around, we would speak Lithuanian. He would insist we speak Lithuanian at home. Of course, when he wasn't around, it was just the kids playing, we would revert to English because it was easier for us. But Lithuanian was pretty common at home.

ZIERLER: You picked it up? You can speak Lithuanian?

ZMUIDZINAS: Yes. We were living not far from John Marshall High School in Los Angeles at the time, actually the high school Barry Barish attended. Of course, this was years after Barry went there, so I wouldn't have seen him on the streets. It was near a Catholic parish, St. Casimir's, a Lithuanian Catholic parish started mostly by the post-World War II immigrants from Lithuania, although there had been several earlier waves of immigration into the US. It was really the post-World War II immigrants who were most active. I was living two blocks from that parish, and they had a grade school and elementary school, which is where I went to school. On Saturdays, they had Lithuanian Saturday school, which I also attended, and they would have Lithuanian language classes, they'd make us sing and dance, all kinds of stuff. That certainly helped me learn Lithuanian. But since my mother learned it later in life, and Lithuanian is an intricate language, the verbs are conjugated, the nouns are declined, the adjectives also, the endings of the words change depending on their usage, and it's difficult to get all that right. My mother would make mistakes, and I inherited some of those mistakes. But the Lithuanian Saturday school helped correct many. But not all. [Laugh]

ZIERLER: Did you stay in parochial school through high school?

ZMUIDZINAS: My family moved in 1971 from this house near Marshall High. That was the house my parents moved to after my dad finished his PhD. But it was getting too small for the family. By 1971, we moved to Glendale, to a house two blocks down the hill from Brand Park. I spent at least one more year going to St. Casimir, living in Glendale, then switched to the Glendale public schools from 8th grade through high school.

ZIERLER: It was the math and science curriculum in public school that was formative for you.

ZMUIDZINAS: Yes. This parochial school was a mixed bag in terms of the teaching. We had some teachers who were excellent. My 5th grade teacher was really excellent. There were a few more maybe in the earlier grades I remember being excellent. But we had some really very poor teachers also, and I'll give you a little example. In 4th grade, we had this teacher who was from Chicago, relocated to Los Angeles, and we were doing science, reading from the book. Of course, this was at the time of the moon landing, so that was a hot topic. The topic was gravity on the moon. There was a statement in the book that your weight on the moon is 1/6 that on the earth because the gravity is weaker. As an example, if you weigh 60 pounds on earth, which might've been a normal weight for a 4th grader, on the moon, you would weigh ten pounds. That seemed fine. The teacher decided to test the class's understanding, so she asked, "How do you figure out what you weigh on the moon?" Some kid raised his hand and said, "Subtract 50 pounds," and she said, "That's right." I raised my hand and said, "But the book says it's 1/6." She said, "No, you subtract 50 pounds." I went home very confused, and I went to my dad and asked him, "What's going on here?" He filled up a page with Newton's laws and so on, which I had no understanding of. [Laugh]

ZIERLER: You get hammered from both sides.

ZMUIDZINAS: But I dutifully brought this piece of paper and offered it to the teacher. I said, "I asked my dad, and here's what he said." The teacher got angry at me and said, "No, you subtract 50 pounds. The astronauts went up and proved it." [Laugh] That was that.

ZIERLER: Moving into the 1970s, all of the excitement at JPL, did that register with you at all, what was happening there?

ZMUIDZINAS: I would hear it at home. Actually, it was my mom who would more often bring up the topic, whether at dinner or just one-on-one. She would tell me a little bit about what was going on with the JPL missions. I knew a little the names, Surveyor, Mariner, and so on. This was more in the 60s. In the 1970s, I'd say, I started paying less attention during my junior high and even high school years. Even after I got interested in math and science, I didn't really return to thinking about what JPL was doing, really, until I started at Caltech.

ZIERLER: When it was time to start thinking about colleges, was Caltech the be-all and end-all for you? Or was it more of a local school?

ZMUIDZINAS: I'd gotten interested in math and science, and I started pushing myself. After 9th grade, I decided I wanted to take summer school. I took the next math course that was coming up, which was geometry. They packed a yearlong high school geometry course into the summer. That allowed me, starting in 10th grade, to move to the course that the juniors would be taking, which was trigonometry. I kept doing that. I kept taking courses to push myself forward. By the time I reached my junior year, my sister had started at UCLA. She graduated high school and started college. I took her calculus textbook, and on my own, I started reading it and working out the problems. I was having fun doing that. Then, I decided that as a senior, I was going to run out of courses to take. I would have finished all the math courses. In fact, calculus was not usually offered at my high school. People went to the local community college, Glendale College, if they wanted to take calculus in their senior year, and it was only one or two students who would do that, a very small number. I realized I wouldn't even be able to do that because I was going to be done reading this calculus textbook before I became a senior. I started to think about what I should be doing. I thought, "Maybe I could just switch to Glendale College and take all my courses there."

Then, I thought, "Maybe I should aim a little higher, maybe I'll try UCLA." That was going to be my plan. I was going to try to take courses senior year at UCLA. Then, my dad said, "Why don't you apply to Caltech?" I thought he was nuts. But I thought, "OK, I'll give it a shot." At this point, I had been spending time in the high school counseling center, which had kind of a little library full of college catalogues from all over the country. I was reading all the catalogues. I read all the Ivy League catalogues, I read Caltech obviously, MIT, Harvey Mudd, anything I could find. I was learning about what might be an interesting place to go. I was already thinking about it. But I decided to apply only to UCLA and Caltech because I was just a junior. I was thinking of it in terms of, "What am I going to do senior year?" I thought, "I'll go to UCLA, and after that, I can apply. Or if lightning hits, and I get into Caltech, then I'll go to Caltech." Lightning struck. They let me in. And that's how I got to Caltech.

Back then, Caltech would visit high schools to interview applicants. I remember being interviewed by Thad Vreeland, professor of materials science, and Louise Saffman, then an undergrad in astronomy, and daughter of Phil Saffman, who was a professor in aeronautics and applied math.

ZIERLER: What was the game plan? What did you want to do at Caltech?

ZMUIDZINAS: By that point, I had decided I wanted to study physics, although I'd say it was only because I enjoyed math. I had started to learn some physics on my own, again, by reading a textbook, and I found it interesting. My father had a colleague whose name is Rimas Vaisnys, he was one of his collaborators, and he was a professor of chemistry at Yale (and later, of geology, electrical engineering, and ecology and evolutionary biology). Also Lithuanian. My father invited him and his family to spend a summer in Pasadena, and they worked together that summer. They had two kids, a boy (Gintaras) and a girl (Vaiva), and Gintaras was maybe two years younger than me. We hung out all summer and got into all kinds of trouble. We ended up going to a scientific supply store, getting chemicals, and mixing our own gunpowder so we could build little rockets. We ended up building a cannon that shot a tennis ball. We would hold a match to the thing. It used lighter fluid. We showed this to my dad's colleague Rimas, and his attitude was, "This is OK if it can be done safely." He told us, "You can't use a match. You can't be standing next to this thing. You've got to be hiding behind that big brick barbecue, and you've got to figure out how you can set this thing off remotely so you don't have to be next to it. That was a challenge. But we solved the problem. We found some old slot car transformers and rigged it up so it could be operated electrically. We'd press a button, we got an old piece of toaster wire, it got hot and set off some matches, which then made the cannon go. Then, my friend's dad came to inspect what we had done to see whether we had done it safely. He was happy with it. He watched us set it off, saw how far the ball went, and said, "How fast is it coming out of the cannon?" This led us to start reading and trying to understand how to figure that out. That's what got me into physics. [Laugh] That little challenge.

ZIERLER: Probably specifically experimental physics.

ZMUIDZINAS: Yeah. By that point, I had started reading Newtonian mechanics to figure out how to do this calculation. Once I started, I didn't stop. I kept going. That's why I was thinking about physics, because I'd started to learn a little bit about it. But I wasn't really sure. I was thinking, "That seems interesting, but we'll see." I was open to the idea that I could easily end up doing something else. So Gintaras' dad gave me a big push by asking some interesting questions. That's partly how I ended up at Caltech a year early. I had lunch at the Athenaeum with Gintaras a few years ago – he's a very successful entrepreneur – and he told me that when he heard I was going to Caltech, he decided that he too would go to college a year early. And he did, at Yale.

ZIERLER: Among the senior faculty at Caltech, were you associated with your father at all? Did they recognize you as your father's son?

ZMUIDZINAS: I'd say not so much. The saying, "The sins of the father are inherited by the son," comes to mind. I didn't really run into that. I seemed to be able to go through Caltech under the radar. Nobody really ever talked to me about my father, which was good. Had I hung out with the particle theorists, they would've known my dad. But as an undergrad, I wasn't doing that.

ZIERLER: Who were some of the mentor figures as an undergraduate at Caltech for you?

ZMUIDZINAS: Probably the biggest influence on me in those years was a result of the fact that I had started working in the cosmic ray group led by Ed Stone and Robbie Vogt. I started in the summer after my freshman year and stayed through graduation. I ended up doing a couple more significant projects while I was there. I worked with various people in the group. There was a graduate student, John Spalding, who was my first mentor, then Dick Mewaldt, who is still at Caltech, I believe. He was my mentor one summer. But then, it was Neil Gehrels, who was a graduate student at the time, who really took me under his wing and gave me these more significant projects to work on related to Voyager. I learned an awful lot from Neil, especially the importance of writing, and to a large extent, how to write a scientific manuscript. I really benefitted from that. Neil is a Caltech Distinguished Alum. He's passed away now. In terms of a close relationship, Neil. But I have a strong memory of a number of the faculty. The physics course, Physics 1, was split into two tracks at the time, track A and track B. Track B was for the people who thought they might be interested in majoring in physics. It was a little faster pace. That was taught by Dave Politzer as a young assistant professor.

I have memories of Dave sitting on the counter in the lecture hall, using his fingers to explain something about rotations. Tom Apostol was our lecturer for Math 1. Really outstanding lecturer. Everything was so crisp and clean. In the discussion section in Math 1, Robert Calderbank was my session leader, equally good. He was a graduate student then. Now he's at Duke. He's married to a famous woman mathematician, Ingrid Daubechies. She was the subject of a long New York Times article a few months ago. Really interesting person. Bob Leighton, I had as a freshman in Physics 10, which was more physics for the masochistic. [Laugh] It was extra topics for freshmen. What I remember about Bob was that he tried to teach us a lot of stuff that I think largely went over our heads. In retrospect, thinking about the subjects he introduced, they were subjects I think he found extremely useful in his career. He was trying to turn us on to those topics. But I wasn't prepared for the things he was trying to get across to us. I would listen, I would pick up part of it, but I would probably miss the essence of what he was trying to tell us, which is a shame. [Laugh] Let me mention one more person, Barry Barish, who was my advisor. I didn't have him in a course, but I would come to see him. He helped guide me to take the right courses, got me on the path.

ZIERLER: What were some of the formative lab courses you took as an undergraduate?

ZMUIDZINAS: In physics, I took a lab course every year, except for senior year. There was freshman lab, sophomore lab, then it was called a senior lab, although I took that course in my junior year. I'd say they were all really formative. Maybe freshman lab was the one that had the largest impact. I've heard that the lab experiments were largely designed and built by Bob Leighton and Vic Neher. They were marvels of mechanical engineering. There was this experiment called the Maxwell top, which had this top spinning on an air bearing and precessing. It was about angular momentum and torque. There were these long air tracks with gliders on them, and with the spring attached, it would be a harmonic oscillator. Without springs, you could have collisions and conservation of momentum. You could replicate all the topics in freshman mechanics in the lab and make measurements.

But what I remember about freshman lab was, we'd have to submit our lab notebooks for grading every week. We would do the experiment, we would take all the measurements, we'd do some calculations, do some writing, and we'd submit it. The first week of work, I submitted my lab notebook and got it back, and there was red ink everywhere. Every page, everywhere I looked, it was red ink. I realized I had not done very well. [Laugh] There were so many comments, I couldn't make heads or tails of what I was doing wrong, so I went and talked to the instructor, Y. C. Chang, who ended up being a professor at the University of Illinois in solid-state physics. I asked him what I was doing wrong, and he said, "You have to calculate sigma. You have to calculate the uncertainty, sigma." That's the thing I hadn't been doing. That's all it took. I realized at that point, "Oh, I get it." [Laugh] And from then on, it was a lesson learned throughout the rest of my life, to calculate sigma. [Laugh]

ZIERLER: Do you remember what Barry was working on in those days?

ZMUIDZINAS: He was a high-energy physicist involved in experiment. To be honest, I don't know what experiments. This would've been the late 70s. (High-energy neutrino experiments at Fermilab). I wasn't paying attention to what experiments Barry was involved in at the time. I mentioned taking a course in relativity from Feynman senior year, which was the beginnings of what turned into LIGO. This was well before Barry got involved in LIGO, more than a decade before.

ZIERLER: With your interactions with Robbie Vogt, were you privy to conversations that would lead ultimately to LIGO?

ZMUIDZINAS: I'll tell you a few things about Robbie. First of all, I would see him because I was spending time in Downs Laboratory, where the cosmic ray group was housed, and I would see him on the floor. But I would only talk to him occasionally. I remember, as a senior, having finished a major project on analyzing Voyager calibration data and writing a big, thick report on that, going over to the division chair's office with Neil Gehrels, who explained what had been done. I think Neil was trying to explain to Robbie that this calibration had been performed, and asking Robbie to look into it and see whether there was anything else we needed to do. I remember that being very intimidating. Robbie was an intimidating person, and the division chair's office was an intimidating place to be. But that meeting went well. It all went OK. I think towards the end of my senior year, I started seeing more of Robbie, especially after that interaction. I would be sitting at my desk in Downs Lab, and Robbie would occasionally pop his head in and say hello.

What I remember him telling me about, it was probably spring my senior year, he started talking to me about all the things happening at Caltech. He did mention the fact that Caltech was starting a gravitational wave detection effort with the hiring of Stan Whitcomb and Ron Drever. And he told me that Caltech was preparing to build a ten-meter telescope on Mauna Kea, led by Tom Phillips and Bob Leighton, and a number of other things that were happening. But I mostly knew about the gravitational wave program from sitting in Feynman's class, just sitting next to these people who were going to be doing it. And Stan Whitcomb, who had been hired as an assistant professor, I knew about well before then because Stan had worked in Robbie Vogt's group as an undergrad and had designed, as an undergrad, an instrument that flew on Voyager, the electron telescope, which was the instrument I had been working on the calibration for. I knew about Stan, he was kind of a legend for designing this instrument as an undergrad. He was well-known in that group, so I knew about him. But he was coming back to Caltech to do something totally different.

ZIERLER: To clarify, in Feynman's class, was he talking about gravitational waves as theoretical constructs, or was he articulating a vision to detect them experimentally?

ZMUIDZINAS: I'll show you this letter. This is page one. You can see he's writing to Viki Weisskopf.

ZIERLER: So this is the origins of the Caltech-MIT partnership in LIGO?

ZMUIDZINAS: No, this predates that. This was 1961. I was about six months old at the time. He wrote to Viki, "Some time ago, you asked me about radiation of gravitational waves. This is a very late answer. I'll give you all the results and how I arrive at them. As you know, I'm studying the problem of quantization of Einstein's general relativity. I'm still working out the details of handling the divergent integrals, which arise in problems." Then, he's comparing it to electrodynamics in 1946. Feynman won the Nobel Prize for quantum electrodynamics and solving the problems of these divergent integrals that show up in quantum electrodynamics using renormalization. He's talking about it in those terms and having problems with these divergent integrals, and he's going to figure out how to do this for gravitation. He's still working on it, but I think he's feeling kind of confident that he might be able to do it. Well, that's an unsolved problem. [Laugh] Feynman was unable to figure out how to deal with them, and no one else since has. Mostly, this letter is about, from a theoretical standpoint, talking about gravitational waves and how you connect general relativity and gravitational waves with quantum mechanics.

The letter goes on to talk about those issues, then towards the end of the letter, he's talking about the possibility of experimental proof that gravitational waves exist, if it's possible to have an experiment that would show that. He's complaining about ideas for measurements where you have a source of gravitational waves and something that's trying to detect them, and they're too close to each other. He says, "Only beyond the wavelength can a clear proof of waves be found." What he's trying to say is, you need to have an object that makes the gravitational waves and something that detects or measures them, and they have to be separated by at least a wavelength, or ideally more than a few wavelengths. For that, he says, "I have not seen any plans for such experiments except by crackpots." We had those two crackpots in our class. [Laugh] This letter was shared with the class at the time in the course we'd been discussing gravitational waves. Feynman had given us a lecture on gravitational waves and had derived for us from Einstein's theory how gravitational waves show up. He was talking to us about orders of magnitude, how strong these was were, or instead how incredibly weak these waves were in various terms. He was also talking about how to understand the waves in physical terms, and this was since the very earliest days, there were questions about whether or not these gravitational waves were real, if it was a correct prediction of Einstein's theory.

The way you approach the problem is, you take Einstein's equations, then you make an assumption that the waves are not too strong. You take these very complicated equations and throw out a lot of the terms because they're small, and you keep only the leading terms. You linearize the equations, basically. Those give you gravitational wave solutions. There was the question of whether something was going wrong in that procedure or not. Einstein wrote a paper in the 1930s where he actually argued that gravitational waves were not real. Apparently, H. P. Robertson, who later was a professor at Caltech, reviewed that paper and pointed out Einstein's mistake. My dad took a course from Robertson, and his notes were later used to help write the relativity textbook by Robertson and Noonan. And Robertson's grandson, Jonathan Fay, taught math at the high school my kids attended. We used to play racquetball. His mom, Marietta Fay, was the wife of Peter Fay, a well-known history professor at Caltech.

Sometime in the 1950s, Feynman apparently attended some general relativity conference, where it was highly mathematical, and people were thinking about relativity and gravitational waves in extremely mathematical terms, and Feynman was thinking about it in very physical terms. He was thinking, "What would happen if you had some object, and a gravitational wave interacted with it? That object could dissipate energy. It could be internal friction in this object, and the object would heat up. If that could happen, gravitational waves must be real." He was thinking about gravitational waves from that perspective, and he was lecturing to us from that perspective.

ZIERLER: Between Robbie Vogt, Ed Stone, and your interface with cosmic ray research, as an undergraduate, was any of that relevant to what was happening at JPL at that time?

ZMUIDZINAS: That's why I was sent for the Jupiter encounter, that connection. The cosmic ray instrument, this electron telescope I was working on the calibration of, was part of a cosmic ray subsystem that was flying on both Voyagers. There was a pretty tight connection with JPL. Like everyone else at Caltech at the time, I was following what was happening with Voyager. I would pay attention to the encounters, and there was a lot of excitement surrounding them. I'd say JPL never felt that far away when I was an undergraduate. And as I mentioned, undergraduates could come to the gate at JPL, and you could show your Caltech ID, and you could go walk on campus. It was very easy in those days. I remember coming to JPL, and I can't remember what for, but I remember doing that on a number of occasions. One of my roommates sophomore year, Rick Vasquez, was working at JPL. He had graduated from Caltech and had taken a job at JPL for a few years, then eventually went to graduate school. But while I was living with him, he was working at JPL after graduation. I would hear about what he was doing. He was working in a group led by Frank Grunthaner. Frank was also a Caltech PhD who was studying the chemistry of the surface of silicon at JPL among other things. I guess you could call him a surface scientist. JPL intersected my life in various ways. I remember going to a party at Frank Grunthaner's house, where a bunch of his JPL colleagues were invited, and somehow I ended up tagging along with my roommate. I remember going to another party, a cosmic ray group party, at some house overlooking the Rose Bowl. I forgot whose house it was, but it was a nice event and a beautiful view looking down. Everyone from the cosmic ray group was there. We were just in the thick of it.

ZIERLER: Did you meet Charles Elachi as an undergraduate?

ZMUIDZINAS: I did not. He was at JPL by then, and it was really only when we started hearing about his radar experiment on the Shuttle and the things it was finding that I became aware of his name. I didn't know him before then. His advisor, Charles Papas, was somebody I knew about as an undergrad, and I believe my dad took a course from him, if I'm not mistaken. But I didn't really know about Charles Elachi back then.

ZIERLER: When it was time to think about graduate school, did you consider Caltech? Did you give thought to staying in Pasadena?

ZMUIDZINAS: The advice everyone was given was, "You should really go somewhere else. You shouldn't stay at Caltech. It's better for you if you go to a different school." I was also, at the same time, wondering if physics was my future. I really had enjoyed it, I especially had enjoyed Feynman's course senior year, but I had ended up taking a lot of courses in economics, there were courses offered in business economics and management, things like accounting (with David Morrisroe) and finance, there was a visiting lecturer from the business school at UCLA (Steven Lippman). I had some interest in those topics as well. My economics professor (Alan Sweezy) told me I should really think about doing a degree in economics. I wasn't sure that was the right path, either. But I was thinking about various options. I was also thinking about perhaps taking a job for a few years, then continuing in graduate school. But I decided I would apply to graduate school in physics. I did, and it was Barry Barish who had suggested I think hard about Berkeley and apply there. That's where I ended up going.

ZIERLER: What was the source of Barry's advice to look at Berkeley?

ZMUIDZINAS: I think because he was a Berkeley product. I was familiar with the Ivy Leagues, MIT, Stanford, etc., but maybe not as familiar with Berkeley as I should have been. With Barry's advice, I started looking at Berkeley, I got interested, and I found they were doing lots of things. Of course, Berkeley has a rich history in physics. That's where I ended up, and very happily so, after the fact.

ZIERLER: Did you have an idea of who you would work with, even before you got there?

ZMUIDZINAS: Given what I know today about applying to graduate school and the kind of advice I give to students, I think I did everything pretty much exactly wrong. [Laugh] I wasn't sure what I wanted to study in physics, and I was honest about that. That's a mistake. You should say you're interested in some particular area, and you should be definite about it. I said I wasn't sure if I wanted to do theory or experiment. That's a mistake. [Laugh] You should definitely choose. And if you have any interest in doing experiment, you should say experiment and not theory. I think if I submitted my application today, it would get summarily rejected. [Laugh] But I came to Berkeley without much of an idea of what I wanted to do. I think I mentioned last time that this was in the early 80s, the Reagan recession was coming on, and really smart people finishing their PhDs in theoretical physics at Berkeley were finding it difficult to find employment. All that percolated down to us first-year students, and I was a TA in a physics for poets course, which is a huge class at Berkeley, a lot of undergraduates trying to fulfill their science requirement, and the head TA was a senior, maybe a fifth- or sixth-year student in theory, who was still unable to find a research advisor, despite the fact that he was really, really smart. I think at that point, I decided I'd better do experiment, and I'd better pick up some practical skills while I was in graduate school. That's how I ended up in astrophysics.

ZIERLER: Of course, Berkeley is so much larger than Caltech. What about the physics department specifically? Did that also feel like a much larger department than at Caltech?

ZMUIDZINAS: It felt larger, but I'd say there was really a community feeling inside the physics department. It really felt like you were part of this community. You felt that you were really in the physics department at Berkeley as opposed to a student in this much larger university. You'd run into students obviously from other departments, but life really centered around the physics department. In the first few years, you're taking courses, you're serving as a TA, and you're trying to find a thesis research project. You end up talking to and meeting a lot of professors. That was interesting. I remember a number of them. Owen Chamberlain was a Nobel Prize winner who was the sweetest man you'd ever meet. He would spend a lot of time with first-year students, guiding them, helping them, especially the students who needed a little extra help to pass the written exams. I remember him teaching some students about Fermi's golden rule – and he had been Fermi's graduate student! I found it to be a very welcoming and very supportive place while I was there.

ZIERLER: Given your sense that astrophysics was where the excitement was, what was broadly going on in the field at that point?

ZMUIDZINAS: My interest in astrophysics was mostly as a vehicle to learn techniques in experimental physics. The project I got involved in, which was building this instrument for the Kuiper Airborne Observatory, involved lasers, microwave electronics, analog and digital electronics, cryogenics, optics. I viewed it as a way of learning a whole bunch of experimental physics techniques. I viewed it less so as where the excitement was. Of course, I started to pick up, over time, once I'd joined the group and started working, what the excitement was. My day-to-day research supervisor was Al Betz, a student of Charles Townes. Townes, after having spent time at MIT as the provost, I believe, moved to Berkeley and established an experimental astrophysics group. I think his idea was to apply modern technology, including lasers, to various areas in astrophysics, but particularly in the infrared and radio, but shorter-wavelength radio. That was interesting because it was a time where there were lots of discoveries being made in those fields, and there was a lot of excitement that I started to understand. 1969, I believe, was the discovery of water in the interstellar medium. In '69 or '70 was the discovery of carbon monoxide. After that came a whole slew of molecules in the interstellar medium.

People, for the first time, were discovering material in our galaxy that really had gone undetected to that point. Molecular clouds, the birthplaces of stars. It was a brand-new area with a lot of work to do and understand. And Townes's group was in the thick of it, studying the problem from various angles. But Townes was interested also in anything and everything having to do with infrared astrophysics, studying the center of the galaxy, which he did with Reinhard Genzel, who was my faculty supervisor. He was the person responsible for tracking my progress towards PhD. Reinhard and Charles Townes, in the 1980s, did studies of the galactic center that were formative for Reinhard and helped lead to his Nobel Prize. I was following all of that. As time went on, the subject just kept unfolding and getting more and more interesting for me. I fell into it for reasons that ended up being different than the reasons I stayed in it.

ZIERLER: How big a gulf were those differences from beginning to completion?

ZMUIDZINAS: The rate of learning in those years was just phenomenal. The rate of learning while I was at Caltech was incredible. Caltech is a place where you simply can't keep up with the rate at which information is thrown at you. The saying is, drinking from a firehose, and that was entirely true. At Berkeley, I'd say, it was a little more manageable as a PhD student. But yet, there was so much to learn and so many opportunities to learn during those years at Berkeley, I felt that I picked up just a huge amount.

ZIERLER: How computational was your thesis? How important was data analysis?

ZMUIDZINAS: In high school, I had an outstanding math teacher by the name of Bill Inhelder (who taught at Hoover High for 45 years), for trigonometry when I was a sophomore, and he also had this course in computer programming at the high school. We had these old Olivetti, which I guess is an Italian firm, programmable desk calculators (Programma 101). They were giant things by today's standards. They had magnetic cards, and you could write a program of up to 120 instructions. You could do very rudimentary things like playing a moon landing game or something like that. That's where I learned how to program, taking that course. At least, I learned how to program that machine. And that got me interested. The same math teacher, the summer after my junior year of high school, before I started Caltech, offered another course in programming, which was now the Fortran language. It was held not at the high school, but at the administration building for the Glendale School District. In the basement, they had a computer they used for administrative functions, payroll and so on. It was a big machine room with this fairly modern Burroughs computer for that day.

We would come in the evenings during the summer, we would spend three hours, we would bring our punch card decks. We'd put them into the card reader, watch the lights blink and the tape spin, our printouts would come out, and we'd analyze where we had misplaced the comma in our stack of cards, fix the error, and go at it again. [Laugh] That's where I learned real computer programming. I picked up the Fortran language, at least at a basic level. I was a little bit prepared by the time I got to Caltech in the summer after freshman year, when I started working with the cosmic ray group. It was to do data analysis. I did several things that summer. I did some Fortran, running Fortran programs to do some data analysis. I didn't really understand too well what was going on. My job was just to do the mechanics of running the program. But then, I also did some programming in the Forth language, which was running on a mini-computer-based real-time data acquisition system, in fact, the same system that had been used to collect the calibration data for this electron telescope that I mentioned earlier. I had started getting involved in computer programming.

Shortly thereafter, the group ended up getting a new computer. It was first a PDP-11/34, then later a PDP-11/70. These were mini-computers, pretty good ones. A graduate student by the name of Rob Pike joined the group from, I believe, University of Toronto in Canada, and he brought with him a tape that contained the Unix operating system. So I think that the cosmic ray group at Caltech had the first Unix installation on the Caltech campus. Rob left Caltech after about a year and joined the Unix team at Bell Labs, and is now at Google. But this was in the early days of Unix. I started learning C programming. I remember my senior year and the summer after, printing out the entire kernel of the Unix operating system and going through each routine in detail, figuring out what this operating system was doing. It was like reading poetry. These guys at Bell Labs, Kernighan, Ritchie, Thompson, and so on, the way they programmed was so elegant. You could only admire it, you could never reproduce it. By the time I got to graduate school, I'd gotten a fair bit of computing experience under my belt. I was not a professional, but I was a reasonable amateur. And I ended up doing an awful lot of programming as a graduate student because in those days, if you wanted to analyze data, you basically had to do it yourself, starting from scratch.

You had to write your own programs. I can't tell you how much programming I did as a graduate student. I could tell you a few of the things I did. I was tasked with the problem of building a low-noise cryogenic microwave amplifier as the second stage of our receiver. We had a high-frequency diode mixer, and the output of that was at microwave frequencies. I had to build a cryogenic low-noise amplifier of the kind that radio astronomers might put on a radio telescope. I had to go dig into all the literature about how they were doing it, then design one of my own and build it. It was a pretty substantial project, except that the software to do microwave design, there was a commercial program that was available on the astronomy department VAX computer. The radio astronomy department at Berkeley had acquired this program and installed it there. The problem was, the entire astronomy department was using this VAX computer, and during the day, you couldn't get anything done. It was so bogged down. That would mean staying up late, working the night shift. Even then, the graduate students were busy crunching their astronomy data, so even then, it wasn't so great.

I decided this was not going to work for me, and I needed to write my own software so I could run it on the IBM PC our group had acquired and was sitting in the lab. I ended up writing, in Fortran, a piece of software that was basically replicating much of the functionality of this commercial software package. It would analyze microwave circuits using the same syntax, using the same approach as this commercial software. I don't know how long that program was, but maybe 7,000 lines of code or something like that by the time I was done. That was extremely useful for me because it forced me to really understand microwave theory, all the ins and outs. It was a learning exercise as well. There were many other things like that. I ended up writing the data acquisition system we used for acquiring and recording data on our airborne flights, which involved interfacing with hardware, writing assembly language code to service the hardware, then lots and lots of code to analyze data. But in comparison to what people do today, it was pretty crude. Today, you get Python. The entire world has written all kinds of routines you can use to fit your data, to crunch it, to plot it, to manage it, whatever. Back in those days, you had to create everything from scratch. One of the god-sends that really helped was the publication of this book called Numerical Recipes. Bill Press, Saul Teukolsky et al. Maybe you've run into it. But having that book show up, having all the routines in that book, having the written descriptions was like a gift from the heavens. It was fantastic. [Laugh]

ZIERLER: What did it specifically allow you to do or at least do more efficiently?

ZMUIDZINAS: Before then, very often, if you needed some basic code just to fit your data, you'd have to either create the routine, or if you were lucky, you could find a paper that described the routine and the algorithm that you could implement. But you were off in the wilderness, off on your own. Here, in this one book, pretty much any kind of numerical routine was in there, whether it was to solve a linear system, to minimize a function, all kinds of extremely useful things. You could not only get your hands on the actual code–it came with these floppy disks you could stick in your PC and take the source code–but you could also read the chapters and understand what it was doing. If you needed, you could dig into the code and change it to make it do what you wanted it to do. It just was a huge time-saver, but also a great educational tool. I remember just being so happy to have that available. [Laugh]

ZIERLER: More broadly, for your thesis, what was happening in the world of interstellar medium research at that point, and how was your thesis responsive to some of those questions?

ZMUIDZINAS: The 1970s were an era of discovery, an initial exploration of the molecular component of the interstellar medium, the dense gas from which stars are formed. In the beginning, there was a period where it was just discovery of molecules. "What's in this medium?" and the surprising richness of the chemistry. Then, there was a mapping of the medium, where there were people like Pat Thaddeus, who was a professor initially at Columbia and later at Harvard, who had a small telescope equipped with a sensitive receiver of the kind that Tom Phillips invented, and they were making maps of the entire galaxy, producing images that showed you where these molecular clouds were in our galaxy. People were just trying to get their arms around where these clouds were, what they were doing, what was in them, and eventually, how stars formed from them. Tom Phillips made several discoveries in the late 1970s, and this was also flying on the Kuiper, in response to this challenge from Arno Penzias. I mentioned to you that Arno had challenged him to make a better receiver, and Tom did, and he was flying it on the Kuiper, and it was working at frequencies higher than anyone else was able to work at at the time.

Tom used that receiver to discover not a molecule, but an atom, neutral carbon atoms, in this dense interstellar medium and a wavelength of 610 microns, a frequency of 492 gigahertz. What Tom discovered was, there was an awful lot of carbon. It became kind of a mystery, this abundance of carbon. At the time, the thinking was, "You have the dense interstellar medium. It comes with a lot of molecules like CO and others in the gas phase, but there's also dust in this dense interstellar medium. The dust makes these clouds opaque to visible and ultraviolet light produced by stars. But at the surfaces of these clouds, you could imagine that if these clouds had given birth to some stars, you could have some young stars near one of these clouds, especially if you had more massive stars that produced a lot of ultraviolet. You could have this ultraviolet light shining on the surface of these clouds, and the ultraviolet would penetrate a little bit governed by the absorption and scattering by dust. But it would break up the molecules, photo-dissociate the molecules at the surface. The ultraviolet photons would have enough energy to do that. It was thought that in that layer, because the ultraviolet light was breaking up the molecules, that you could have a thin layer of carbon.

What Tom was finding was that there seemed to be more carbon, perhaps quite a bit more, than you could explain in this way. There was a little bit of a mystery about how much carbon there was, and if there was as much carbon as some of Tom's measurements seemed to indicate, what the heck was going on? That was one of the topics of my thesis. There was another spectral line of carbon you could get to at 809 gigahertz, a frequency that was higher than Tom's receiver could reach but was within reach of the receiver we built. By comparing the 809 gigahertz measurements against Tom's measurements, we could get a better handle on how much carbon there was. That was one big part of my thesis. The answer from that was, there was still a lot, but perhaps not as much as the worst case. It bounded the problem a little bit. But then, there was also ionized carbon, which was at a much higher frequency, at 1,900 gigahertz, or 1.9 terahertz. Ionized carbon could also be produced in those regions, but by then, it was known that there was quite a bit of ionized carbon. Ionized carbon was actually a very bright spectral line. Reinhard Genzel and Charles Townes, flying on the Kuiper in the mid-1980s, started studying galaxies using a different instrument and started to look at ionized carbon towards nearby galaxies. They were finding that it was an impressively bright spectral line. In some cases, it looked like this one spectral line could account for approaching 1% of the entire energy output of a galaxy, just an impressive amount of energy to be collected and emitted in one spectral line.

Understanding what was going on with ionized carbon, where this emission was coming from, what more we could learn about it was an important problem. Our instrument was able to spectrally resolve the line, not just detect the fact that there was a spectral line but look at the details of the line shape. By doing that, you could understand how the gas that was emitting this ionized carbon spectral line was related to the molecular gas. Did it have the same spectral line profile, or was it different? It would give you clues about the emission region. That was part of my thesis as well, and we found some interesting things that were later rediscovered by the Herschel mission 20 years later. The fact that you often see ionized carbon in absorption as well, not just in emission. All of this relates to what's happening with ALMA today. ALMA is studying galaxies at extremely large redshifts, in the very early history of the universe, using the ionized carbon spectral line because it's such a powerful line. It allows ALMA to see to great distances. Of course, because of the red shift, you can do it from the ground. 1.9 terahertz, you can't see that from the ground. You have to be in a plane, in a balloon, or in space. But when the redshift is six or seven, you can easily see it from the ground. It shifts to long wavelengths that can get through the earth's atmosphere. That part of my thesis was very early work on a topic, ionized carbon, which has considerable relevance today still.

ZIERLER: On the building stuff side of things, was there anything relevant in either materials science or engineering, any advances at that point that made your research possible?

ZMUIDZINAS: We were benefitting a lot from, you could say, advances in electronics writ large. The laser we used was a gas laser. It was a carbon dioxide laser with a high-voltage discharge. The thing glowed kind of like a neon tube. Of course, it had CO2 inside. Then, the CO2 laser would produce radiation at an infrared wavelength around ten microns, then that would go into another tube that was filled with some kind of strange gas like ammonia, difluoromethane, or some other molecule that the CO2 laser would pump into some excited state, then there would be a lasing transition in the far infrared that we would use to drive our receiver. Optically-pumped far-infrared lasers, I forget how far back they go (circa 1970), but they were certainly known a decade before we were using them, and it wasn't like that technology was really going to go anywhere. It was big, bulky, clunky, and difficult to manage. But the advances were mostly in electronics and semiconductor devices. Our detector, the thing that received the light from the telescope, was a gallium arsenide Schottky diode that was produced by this group led by Bob Mattauch at the University of Virginia.

The descendants of that group are still around. There's a company called Virginia Diodes, which is quite active today and produces components for this part of the spectrum, the submillimeter and far-infrared. Their technology is very far advanced from what it was back then. But it was Mattauch's group in the electrical engineering department at the University of Virginia that was producing these things for us and others. Then, after that, the cryogenic microwave amplifier that I mentioned, there, we were really benefitting from what was going on in industry. Gallium arsenide transistors for microwave frequencies were really getting developed in those years, and it made a big difference to us as well as all of radio astronomy. In the late 1970s, Sandy Weinreb, who's still around at Caltech, very famous in radio astronomy, especially instrumentation, had started working with cryogenic transistor amplifiers and found that the noise performance could be competitive with the other kinds of amplifiers being used back then, parametric amplifiers using semiconductor diodes. So, a switch happened in the early 80s to using these cooled transistor amplifiers, and that was a big deal for us. Five years before, we would not have been able to build the receiver that we built. For the rest of the microwave electronics in the signal chain, we were benefitting from what was happening in industry. Any experiment of that era was in the same situation we were. We were riding the wave of stuff coming out of Silicon Valley, whether it was analog electronics, lower-noise analog components, digital electronics. The fact that we were able to acquire data using PCs was a big deal, a big change.

ZIERLER: On the other side, from the building and engineering side, was your work connected to theory? Were there theories in astrophysics at that point that served as guideposts? Or were theorists interested in what you were doing at the time?

ZMUIDZINAS: There was a famous paper, which was kind of our guidepost, by Xander Tielens and Dave Hollenbach, both of whom were at NASA Ames at the time, and it was a comprehensive model of what should be happening in these so-called photodissociation regions, where you would have a molecular cloud surface exposed to ultraviolet radiation. They had constructed a detailed model of the physics and chemistry that should be happening in those regions. They were worried about mechanisms for heating and cooling, how the energy in ultraviolet light was absorbed, where it went, how it was reradiated back into space, the photochemistry, but also the ion-molecule chemistry in those regions, what it all meant for the temperature distribution in these regions, what it meant for the distribution of different chemical species, etc. They were really looking in detail, trying to assemble all of the knowledge that was then available about these things, trying to construct a detailed theoretical - actually computational - model of what these regions should look like.

That was one paper that was really important. By my description, I think you can tell, there were an awful lot of things to worry about. It was a big, fat paper with lots and lots of material in it. [Laugh] You learned a lot by studying that paper. But the difficulty is that it's really hard to confront the theory with experiment in a really rigorous way because there are so many unknowns still. I think only later did it start to become clear that things were a little more complicated, that you shouldn't really think of these regions as just having a single surface, that the interstellar medium, because of turbulence, has really got a complicated structure. You could think of it as being clumpy, being fractal. There isn't just a single surface. There could be regions that are dense, and also regions that are not dense where the light is able to penetrate further. The whole situation is considerably more complicated than represented in this Tielens and Hollenbach paper. But nonetheless, I'd say there certainly was plenty of work happening, plenty of interest on the theory side to make use of and to compare to.

ZIERLER: Last question for today, besides Betz and McKee, who else was on your thesis committee?

ZMUIDZINAS: Paul Richards. And Jack Welch. I think I mentioned that Chris McKee took over for Reinhard when Reinhard moved back to Germany in 1986. Jack was a radio astronomer who led the development of the millimeter interferometer at Hat Creek, which later became the Berkeley-Illinois-Maryland Array, or BIMA, and later, under Anneila Sargent's leadership, ended up joining with the millimeter array at Owens Valley. Together, they formed something called CARMA, which was the California Association for Research and Millimeter Astronomy, and which combined the millimeter telescopes from BIMA and Owens Valley, but now moved to a higher site above the Owens Valley floor. They operated for a while, and that was an important precursor to ALMA. Both in terms of science and technology, they were preparing the way for ALMA. So that was Jack Welch. Jack was one of the advisors of John Carlstrom, who was my classmate at Berkeley, who then came to Caltech as an assistant professor, and we worked closely together until he left for Chicago. He's now the Chandrasekhar Professor at Chicago, and is quite famous in the cosmic microwave background field. I knew Jack also through John because John would tell me about what he was working on.

Then, Paul Richards was Andrew Lange's thesis advisor and John Mather's thesis advisor. John, of course, won the Nobel Prize in physics for the work he did with COBE, the Cosmic Background Explorer, a NASA satellite. Paul was, I'd say, a real dominant figure in millimeter and far-infrared cosmology and astrophysics throughout his career. He and Tom Phillips, I'd say, really had parallel careers. In fact, both of them are co-inventors of the superconducting tunnel-junction mixers that ALMA uses. But it was Tom that actually went on to use them for astronomy, whereas Paul Richards's group did some lab experiments and focused on showing that you could get low noise performance approaching the limits set by quantum mechanics.

But his heart was more in the microwave background work and focused more on microwave background balloon projects as opposed to using the superconducting receivers for astronomy. And that's what Andrew Lange was involved in. He was involved in a rocket experiment as Paul's graduate student, looking not at the cosmic microwave background, per se, but trying to see, at shorter wavelengths, what was going on. His rocket experiment, which was a collaboration with Japan, they thought they had measured excess radiation at shorter wavelengths, which later turned out not to be correct. It turned out that the far-infrared background they thought they found wasn't there at the end of the day. But the true far-infrared background was discovered by COBE in the mid-90s. Paul was on my thesis committee, and in 2003, Paul and I wrote a review paper together on superconducting detectors for millimeter and submillimeter astronomy.

ZIERLER: On that note, we'll pick up next time post-graduate life, moving forward.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Monday, March 21, 2022. I'm delighted to be back with Professor Jonas Zmuidzinas. Jonas, it's great to be with you again. Thanks for joining me.

ZMUIDZINAS: Likewise. Good to be with you, David. Thank you.

ZIERLER: As you're wrapping up your post-doc in 1989, did Caltech recruit you? Were you on the job market more generally at that point?

ZMUIDZINAS: The answer is yes and yes. I'm going to rewind slightly. I think I told you that when I was finishing graduate school, the way I ended up at Illinois was, I learned that Fred Lo, who had been an assistant professor at Caltech and had worked on the millimeter interferometer with Bob Leighton, Tom Phillips, and others, didn't receive tenure at Caltech, so he was moving to the University of Illinois and decided he had interest in starting a millimeter/submillimeter astronomy program, including instrumentation, there. I talked to him at the Pasadena American Astronomical Society meeting, and he ended up offering me a post-doc to come to Illinois. That's where I started to learn about superconductivity. My interest in all that came because as a graduate student, I was flying on the Kuiper Airborne Observatory with this laser instrument I mentioned, and for the flight series, we would go to NASA Ames in Mountain View, California. That is where the plane was based, and we used the runways there at Moffet Field. Sometimes Tom Phillips, who then was a professor at Caltech, would also be there flying his instrument. One of the graduate students involved in that project was Geoff Blake, who's a professor here now.

I had known Geoff since my freshman year at Caltech. We were freshmen together. Then, he left for Duke and came back to Caltech as a grad student. Geoff was telling me about the work he was doing using superconducting receivers at Owens Valley, showing me the data coming from these beautiful very-low-noise receivers. It was seeing Geoff's thesis data, and marveling at just how spectacular those data were that got me interested in working on superconducting receivers. That's how I ended up at Illinois to pursue that. Two years later, already, at Illinois, Fred Lo and others were starting to take action to offer me a faculty position there, which was going to be a joint position between electrical engineering and astronomy. I was also interested in a few other places as well. I had a number of interviews. One day, the phone rang. I was on the job market, trying to figure out my next step. It was Tom Phillips. He said, "We'd like you to apply for a job at Caltech." [Laugh] A, that was the last thing I ever expected would happen in my life, and B, it was very daunting to think about both applying and eventually coming to Caltech as a faculty member. But that's what happened. I came, I had an interview, they offered a position, and it was just not possible to turn down that opportunity.

ZIERLER: Just to zoom out for a second, how mature a subfield is submillimeter astronomy circa 1989?

ZMUIDZINAS: Circa 1989, it's a very small field. There are pioneers like Tom Phillips working hard to create and define this field. There were a few groups in the US. There was Tom's group, this Berkeley group I was part of with Charles Townes, Reinhard Genzel, and Al Betz. They basically entered this area when I started graduate school in the early 1980s. You're familiar with these decadal surveys. We just had one, Astro2020. There was supposed to be a decadal survey in 1980, but I think it came out in '81 or '82, and it was called the Field Report. They recommended building a ten-meter telescope, which turned out to be the Caltech Submillimeter Observatory, the CSO. There was also recommendation in that report for something called the Large Deployable Reflector, which was supposed to be a space project, a 10- or 20-meter telescope in space that would work in the submillimeter and far-infrared. And that got NASA to start investing in the technology that would be needed for such a project. Things were picking up steam, and by the time I joined Caltech at the very end of 1989, beginning of 1990, the CSO had been completed. There was a conference in Kona, Hawaii, the year before, in 1988, to celebrate the opening of both the CSO and the 15-meter James Clerk Maxwell Telescope, JCMT, which is adjacent to the CSO on Mauna Kea. That was a project that UK, the Netherlands, and Canada were involved in. The field was opening up. These were the first big telescopes that were available, there was money starting to be invested in developing the instrumentation and technology. It was early days, but it was starting to blossom. It was a good time to be working in the field.

ZIERLER: Tom Phillips was a pioneer in what way? Was he using extant technology in new ways? Was he asking different questions? What exactly was he pioneering at this time?

ZMUIDZINAS: I think I mentioned the story of how Arno Penzias at Bell Labs challenged Tom to build a better receiver, so he did. This was in the early 70s, shortly after the discovery of interstellar carbon monoxide. Tom first developed something called an Indium Antimonide Hot Electron Bolometer receiver. Indium antimonide is an unusual kind of semiconductor, and Tom knew from being a low-temperature physicist that he could use it as a sensitive detector at these wavelengths and that it was fast enough and had a short enough response time that he could usefully make a radio receiver with it. It wasn't as fast as perhaps he would've liked, but it was enough to get going in the field. And that was its major limitation, the bandwidth of the device was narrow. But to solve that problem, in the late 70s, Tom invented the device we use today, the superconducting tunnel junction (SIS) mixer, which is the heart of the submillimeter receiver, the thing that makes it work. It's the device that ALMA, the world's largest ground-based astronomy project, relies on and fundamentally enables it.

Tom was watching what was happening at Bell Labs in superconducting devices, and there was a fairly sizable investment going on in superconducting computing. A much larger investment was being made at IBM. They thought this was going to be the technology for the next generation of large-scale mainframes. They were pushing it hard and throwing a lot of money into it. All of this had a spillover benefit for Tom because he was able to get these small-area tunnel junctions that he needed for these SIS receivers, there were people who could make them, and he could test them. That's how that invention happened. Tom took advantage of that opportunity and showed that you could make a sensitive receiver at millimeter/submillimeter wavelengths this way. And it took a while. There were a lot of skeptics. Tom had to put these receivers on telescopes and start taking data. Eventually, it became clear to everyone in the field that this was the future, that this was going to displace the other technologies, particularly semiconductor diode technologies that were being used. By the time I came to Caltech in 1989, it was clear that the SIS technology was going to take over the field, but there was a lot of work left over to do. The first devices were still pretty crude and hadn't reached up to higher frequencies, where you really wanted to be using them. That was the task I was looking at when I started on the faculty, how to really take this nascent technology and advance it to higher frequencies.

ZIERLER: Was your sense that Tom's recruitment of you was part of a larger effort to make Caltech a center for submillimeter astronomy? Or was he looking more for a junior partner, and it would be the two of you who would work on this?

ZMUIDZINAS: Caltech faculty positions are limited. [Laugh] There are not very many of them. There was the millimeter interferometer at Owens Valley, which Tom had helped get going and turned it into a viable astronomical instrument in the early 80s, while he was waiting to raise the funding to build the CSO. There were actually two observatories that were closely related, Owens Valley and the CSO. They relied on much the same technology. But Tom's ultimate goal was a space mission. He'd participated in the effort that led to the recommendation for the Large Deployable Reflector in the 1982 Field Report, but Tom understood that the starting point almost certainly wouldn't be a 10- or 20-meter, multi-billion-dollar space observatory, but something smaller was the right starting point. By the mid-80s, he was proposing with JPL to NASA for something called the submillimeter explorer, which was a small, scaled-down mission, and then there were various subsequent proposals along those lines with JPL. Ultimately, all that led to involvement with the European Space Agency on the Herschel mission. When I came in 1989, 1990, the grand vision wasn't the ground-based observatories, it was to go to space. The ground-based observatories were a way to advance the science and demonstrate the technology to allow a space mission to happen, to generate enough interest in the science and show that the technology would work for a space mission. This was Tom's dream, to get into space. You could say that I was hired, I suppose, with the idea that one person couldn't do everything. [Laugh] But maybe two people could. Of course, it's not just the two people. Those were the faculty positions. There were a lot of students, post-docs, staff, people at JPL, and so on.

ZIERLER: Of course, a perennial question for Caltech and its astronomy: how does it maintain its world-leading status? With that in mind, where did submillimeter astronomy loom in those larger questions about the things Caltech would do to stay ahead of the curve? Was submillimeter astronomy in 1989 very much envisioned as one of the things that was going to maintain Caltech's leadership in the field?

ZMUIDZINAS: Astronomy initially meant only astronomy of visible light. Then, grudgingly, astronomy using radio waves was viewed to be part of astronomy, then infrared, x-ray, and so on. These different fields were opening up, starting in the 1950s with radio astronomy, then in earnest in the 1960s with infrared, x-ray, and so on. Submillimeter astronomy was one of the last, you could say, wavelength or frequency frontiers to really get going. Even by 1990, it was still a very young field with a lot of promise. It was viewed at Caltech as being a good place to be pushing, to open up that field. This is something I think Bob Leighton already, in the early 1970s, had envisioned. He was working with Gerry Neugebauer in the 1960s on infrared telescopes, and he and Gerry developed an inexpensive telescope that they used to do infrared sky surveys. The next thing Bob Leighton did was to start working on millimeter/submillimeter telescopes, these ten-meter telescopes that ended up being used at Owens Valley and for the CSO. I think Bob Leighton, circa 1970, was seeing pretty clearly that this was an interesting field to be pursuing. That was the time when molecular astronomy, the discovery of the interstellar molecular medium, was happening, and there were lots of discoveries in infrared astronomy and interest in pushing those instruments to longer wavelengths. That was also, I think, part of Bob's thinking. It was really Bob who identified this field and voted with his feet, started working on the telescopes. This was a time when Bob was PMA division chair in the early 1970s. I think it was really Bob who set the course for millimeter/submillimeter astronomy at Caltech. That's what led to Tom being hired, then Tom being hired led to me being hired.

ZIERLER: The perennial questions about the tradeoffs in land-based and space-based telescope projects, how were those specifically tied to questions for submillimeter astronomy, when to do a land-based project and when to do a space-based project?

ZMUIDZINAS: In the submillimeter, it's really water vapor in the earth atmosphere that is the controlling factor.

ZIERLER: You want to build in a desert.

ZMUIDZINAS: Yes, you need to build on a high, dry site. You want to get up above most of the water vapor, and you want to do that in a place on the surface of the earth where there's ideally less water in the atmosphere above you. Mauna Kea on Hawaii is pretty good. Where ALMA is sited in Chile on the Atacama Plateau is somewhat better. There are high mountaintops above the Atacama Plateau that are even better. Of course, the altitude is getting pretty high by that point. The ALMA plateau is 15,000 feet altitude, about 5,000 meters. The South Pole, Antarctica more generally, is also an excellent place. That's where the submillimeter telescopes ended up getting built, at places like that. But even after doing that, when you start pushing into shorter wavelengths in the submillimeter, what happens is that you can see through the earth's atmosphere from these high, dry sites only in restricted wavelength or frequency intervals, transmission windows where the atmosphere is not totally opaque.

The frequency spectrum is chopped up into these windows that are accessible from the ground. But as you go to higher frequency or shorter wavelengths, eventually, the water lines, the absorption by atmospheric water vapor, comes in so thick and heavy that it just shuts down, you can't go higher. That happens at a frequency at about 900 gigahertz, a wavelength of about 300 micrometers. Anything shorter than that, the atmosphere's opaque. You have to go on an airplane, a balloon, or ideally, space if you want to go to shorter wavelengths. But there are advantages for going to space, even if the atmosphere's partially transmissive, and that's especially true if you can cool the telescope and reduce the background radiation incident on the instrument. You can have a very sensitive instrument if you cool the telescope. This tradeoff between ground and space is on everyone's minds. Space projects have to convincingly explain why they need to be in space because it's a lot of money to go to space. If you can do something on the ground and do it effectively, that's often the best way to do it. ALMA, this large array in Chile, is a good example of really exploiting the opportunity from the ground and trying to maximize that opportunity, going big with lots of telescopes with really sensitive receivers. That's why it cost roughly a billion, billion-and-a-half dollars to build.

ZIERLER: Was JPL an asset for you right from the beginning when you joined the faculty at Caltech?

ZMUIDZINAS: Absolutely. I know this history to some degree, although there may be people who know it better, but back in the early 1980s, and this was probably at the time that Bruce Murray was serving as JPL director, there was a period where JPL's future in these large planetary missions was not totally certain. Bruce was busy trying to keep that line of business going for JPL, let's put it that way. But there was also interest in finding other ways that JPL could serve NASA. After Bruce Murray came Lew Allen, and it was during his time, I believe, that the idea of building a microdevices laboratory started to get developed. Lew Allen and others made it happen. They convinced NASA to invest in the facility, to build the building, and to at least partially equip it. There was other funding that came in, I think, through the DOD. This was during the Star Wars era. By the time I arrived, there was this beautiful new facility that was just being opened up. The group working on superconducting devices had been there since the early 80s, and they were connected with Tom. Tom was encouraging them to develop the kinds of superconducting tunnel junctions he would need for CSO but also for possible future space missions, so there was already early technology development work happening at JPL.

When I came in, there was this beautiful new facility, there was a group of really good people, including Rick LeDuc, my very longtime collaborator, ready to start making use of that facility. One of the first things I did when I came to Caltech was that I became a user. I would gown up and spend time working in the clean room in that new building alongside Rick LeDuc and others. That, for me, was a really essential part of my research activities. Without the microdevices lab, I wouldn't have been able to do basically almost anything I've done in my career. [Laugh] And I was coming from the University of Illinois, where I was working with a graduate student, Fred Sharifi from Dale Van Harlingen's group, rummaging through old parts, scrounging together the equipment we needed to make these superconducting tunnel junctions. To say we were doing it on a shoestring, I think, is overstating it. [Laugh] Nonetheless, we managed to put together the equipment we needed, scrounging and borrowing wherever we could. I had a pretty good appreciation of both the fact that it wasn't easy in a university lab to put this together and the importance of having really good tools to do this very difficult work. Whenever you start a job, you should try to get the best tools available if you want it to go well. Here, at JPL, we had this beautiful new lab, beautiful new equipment, and it was all ready to go.

ZIERLER: The day-in and day-out of being focused on the instrumentation, if you had the chance at that point to step back, what were the big questions in astronomy generally at that point for which submillimeter astronomy offered some exciting possibilities?

ZMUIDZINAS: Well, submillimeter astronomy, millimeter astronomy, astronomy at these longer wavelengths, allowed you to study, you could say, material in our galaxy and other galaxies that was responsible for forming stars. This dense phase of the interstellar medium was really only accessible at these wavelengths. To learn something about it, you had to make measurements at these wavelengths. Why is it important? What do you see when you look out in the universe? Stars, galaxies. Where did they come from? How did they arise? What are the inner-workings of star formation? Those are the kinds of questions you could start to answer by working at millimeter and submillimeter wavelengths. Then, as the instrumentation got better, with projects like ALMA, you could start to study these questions not just in our local universe, not just in our own galaxy, but out to the furthest reaches of the universe. Today, ALMA can see galaxies that are at or beyond the redshifts reached by any other facility, including the Hubble Space Telescope.

But crucially, ALMA can also get extremely high angular resolution, so you have these spectacular images of what appear to be planet-forming disks of material, which are basically the remnants of the star formation process, still a disk of material surrounding a young star, but then you look at the disk, and you see there are gaps and rings that are devoid of material. One of the possible explanations is that there's a planet clearing out that gap, a newly formed planet orbiting the star. Back in the early 1990s, in my early days at Caltech, this was all far in the future. We had, I'd say, a pretty good understanding of the kinds of science that could be done in the millimeter/submillimeter. The problem was to actually develop the technology and instrumentation that would allow it to happen. That's what we were focused on. We knew the future was bright scientifically, but that there was a lot of hard work on the technical side to make it happen.

ZIERLER: Being a National Science Foundation Presidential Young Investigator in the 1990s, what did that allow you to do personally, and what are the takeaways there, both in terms of NSF support for submillimeter astronomy and what was happening at Caltech?

ZMUIDZINAS: This was a nice program. I think these days, the equivalent is called PECASE. It was a program where early-career faculty could get five years of support from the NSF. And it wasn't a huge amount of money, but it was money you could decide the use for. You could change directions, you could explore early ideas, and so on. It was a kind of money that is extremely valuable that way. Often, it's difficult to get. Especially, when you're a young faculty member trying to develop a research group and research directions, it's very helpful to have funding like that. I was fortunate because Tom was there already, and as I mentioned, the CSO had been built. That was an NSF-supported facility. It awarded half of the observing time to the national community through a proposal process. Most of the other half the time was for Caltech. The University of Texas, and later JPL, were also involved and got a small share. Observing time on the CSO was available, and there was a lot of instrumentation work for the CSO that was going on that was funded by the NSF grant. I had my own group, but I was benefitting from being in an environment where there were other things happening in my field in this area. A lot of that was the NSF support for the CFO.

ZIERLER: What is the origin story for the discovery of interstellar hydrogen fluoride?

ZMUIDZINAS: [Laugh] Very good question. On the Kuiper Airborne Observatory–as a graduate student, I flew on the Kuiper. We'd use these semiconductor diode mixers that weren't very sensitive. That's why I got into the superconducting receiver business. It seemed that it would be a great thing to do to put them on the Kuiper and fly an instrument that had far better sensitivity than I enjoyed as a graduate student.

ZIERLER: What were the advances? What allowed for that better sensitivity?

ZMUIDZINAS: We took Tom's invention, the superconducting tunnel junction mixer, with design ideas I'd started working on as a post-doc at Illinois and really carried forward and added to once I got to Caltech. We were able to develop mixers and receivers using these superconducting tunnel junctions that were produced at the JPL Microdevices Lab. I was actually personally involved in producing the early versions of them, then Rick LeDuc, Jeff Stern, and other collaborators got involved and carried that on, producing these devices. We were able to build receivers at frequencies starting at 500 gigahertz, at wavelength of about 600 microns, on up to above 800 gigahertz by the time we were done on the Kuiper (and later, up to 1250 gigahertz for Herschel). We were building SIS receivers at frequencies they really hadn't been used before, and we were achieving sensitivities that hadn't been achieved before.

We were taking Tom's invention, pushing it up in frequency, making it work, and showing that the instrument would perform well in an astronomical sense, that you would get high-quality astronomical data. We were pioneering these higher-frequency SIS mixers, and we were pioneering the technology. Our designs incorporated a lot of things that hadn't been used or demonstrated before. That was all working really well, and one of the things we did was to study interstellar water. Now, even from airplane altitudes, you simply can't observe interstellar water if what you're looking for is the garden-variety version of water, which is, as you know, H2O, where O is the oxygen-16 isotope, which means eight protons and eight neutrons in the nucleus. But there's another isotope, oxygen-18, which has two extra neutrons in the nucleus that make it a little heavier. What we're looking at are rotational transitions. These H2O molecules, there are in the shape of little Vs. In fact, Linus Pauling's house is a block away from my house. He built the two wings of his house to have exactly the bond angle of water, to the consternation of his contractor.

ZIERLER: [Laugh] That's great.

ZMUIDZINAS: Probably, it was Linus Pauling who understood why the angle was what it was. That's another story. You have these Vs with the oxygen in the middle, these two hydrogens sticking out, and this thing is spinning end-over-end in some weird, complicated way, and that gives rise to its submillimeter transitions between the rotational energy levels. If you use the oxygen-18 isotope, it's a little heavier and spins more slowly, and the transitions occur at a frequency that's distinct from the oxygen-16 isotope, and you can actually see it through the earth's atmosphere if you're on the Kuiper. The down side of that is that the abundance ratio is a factor of 500. There's a factor of 500 less of this weird oxygen-18 flavor as opposed to the vanilla oxygen-16. That means there's not so many of these H218O molecules in the clouds you're looking for, and that means that the emission or absorption spectral lines are considerably weaker, which means you have to have a high-sensitivity instrument to be able to see them.

That's why you need the superconducting receivers, to be able to see these things. We were the first to actually detect this oxygen-18 isotope in its so-called ground-state rotational transition, the lowest energy transition that allows you to probe colder gas, not gas that's subject to heating from a nearby star or by shocks but trying to study the chemistry of these clouds in their cooler, calmer regions. One of the objects we observed is a molecular cloud called Sagittarius B2 near the center of our galaxy. It's a big, massive cloud, and we observed this oxygen-18 isotope of water and absorption against the radiation produced by the dust grains inside this big, dense cloud. The dust grains are getting heated up by starlight, from stars buried deep inside the cloud, the warm dust grains in the inner regions re-radiate the energy at submillimeter wavelengths, and that radiation has to pass through the outer layers of the cloud to reach us. As it passes through the outer layers of the cloud, we're probing the existence of this interstellar water in the outer layers of the cloud by looking for spectral lines in absorption. We did all this, and to understand the measurements, I ended up needing to write a fairly complicated computer code to calculate the radiative transfer, how the radiation was being produced by these dust grains, how it was passing through these outer layers, and at the end of the day, how we could explain the data we were getting on the Kuiper.

I ended up writing a code and developing a model of this molecular cloud, and it was, for its time, a fairly sophisticated radiative transfer code. Then, David Neufeld, who's a professor at Johns Hopkins, an expert in the interstellar medium and especially the dense interstellar medium, who is very interested in hydride molecules like water, molecules that have maybe one heavier element with hydrogen attached to it, became interested in the possibility of detecting hydrogen fluoride using the ISO satellite, which was a European infrared astronomy satellite that had a far-infrared spectrometer as one of its instruments. He got in touch with me, and we started applying this radiative transfer code I had written for water to the possibility of detecting hydrogen fluoride in the same object, using essentially the same ideas, looking for an absorption. We wrote a proposal to get time to make this measurement, and to my surprise, actually managed to make a detection, and we used my code to interpret the observations. That led to the paper. That's how I fell into it.

ZIERLER: Of course, in the mid and early 1990s, there's so much excitement about COBE, about the cosmic microwave background. What were you following, and what was your involvement in this work?

ZMUIDZINAS: I was not involved in COBE at all. This was a NASA Goddard project primarily, although it had other people like George Smoot at Berkeley involved. I was watching it as a spectator, you could say, but I wasn't really involved in it in any real sense. But of course, we were all interested in the results and were amazed at the black-body spectrum that John Mather showed at the American Physical Society conference. I think he got a standing ovation when he showed it. Then, there was the discovery of the anisotropy of the microwave background, that it wasn't exactly totally uniform everywhere but had some ripples. That was very interesting. For me, one of the really interesting discoveries was, in the mid-90s, 1996 timeframe, was the discovery of the far-infrared or submillimeter excess or background radiation. In addition to the three-degree Kelvin black body radiation that is the cosmic microwave background, at shorter wavelengths, the measurements actually deviated from a perfect black-body curve. There was excess emission at these shorter wavelengths that we now know is the result of starlight being absorbed by interstellar dust and reradiated at those wavelengths.

What COBE was seeing was the net effect of this process in all the galaxies across the universe, all the galaxies that ever lived, producing this far-infrared background. That was very interesting because that said that this was quite an important part of the story of the universe, that there was a lot of energy that was being captured by these dust grains and reradiated at these long wavelengths. That was one of the things, not the only thing, that got me interested in moving away from doing high-resolution spectroscopy of molecules in the interstellar medium and starting to think about building cameras, imagers at these wavelengths, and developing the technology needed to do that. It was clear that if you started mapping the sky at submillimeter wavelengths, you would start to detect galaxies in their dust emission, this mechanism of dust grains capturing starlight and reradiating it, and that would be an interesting way to study the universe, to discover which galaxies were bright in this particular mechanism and try to understand why. Starting in maybe 1994 or so, I began working in that direction, although it took a little while for things to really gel.

ZIERLER: In the 1990s, there are phenomenal advances in computation. There's all of this excitement about supercomputers at the DOE. What was relevant for your research agenda just in being able to take advantage of all of this new ability in computation?

ZMUIDZINAS: I would say that for me, by far, the most important advances were what computer you could put on your desktop. [Laugh] They just kept getting better, and it was marvelous. It's what allowed me to write this radiative transfer model and actually run it on a workstation at the time. As things moved on in the later 90s, the workstations got powerful enough to be able to run the sophisticated electromagnetic simulations, using engineering software to solve Maxwell's equations in three dimensions for the various kinds of structures and components we were using in our receivers. That eliminated a lot of guesswork. You could actually simulate all the fields and figure out how the thing was going to perform before you ever built it. That was a huge advance. But in terms of using real supercomputers, I'd say our experiences were fairly limited. The one example that comes to mind was Rob Schoelkopf's PhD thesis. Rob is now a professor at Yale, a bigwig in quantum computing. But his PhD thesis involved understanding what the limitations were for using superconducting tunnel junctions in millimeter/submillimeter receivers in a different way than Tom Phillips had started using them in the late 70s.

When you have a superconducting tunnel junction, there are two main effects that can happen. You can have single electrons that tunnel from one superconductor to the other through a thin insulating layer, an oxide layer, for instance, of the superconducting material. Or, because it's a superconductor, and in traditional low-temperature superconductors the electrons are paired, you could have an electron pair tunnel across. This pair tunneling leads to what's known as the Josephson effect, after Brian Josephson, who won the Nobel prize for predicting the effect. Rob's thesis was to determine whether you could use the Josephson effect as another way of making sensitive radio receivers. Rob ended up doing a lot of simulations on a Cray supercomputer of how these receivers would perform, trying to understand what the limitations and underlying physics were. Actually, that turned out to be a useful exercise because at the end of the day, he had understood what had escaped the other scientists who previously worked on these questions for several decades, and that was the fundamental noise mechanism in these devices. Through his simulations, he was able to understand that you would never really be able to get these things to work very well. [Laugh] It was a negative result in that sense, but at least he developed a good physical understanding from these supercomputer simulations about why that was the case. That's an example of a supercomputer being applied to do calculations that you couldn't do before, and it led to an important physical insight.

ZIERLER: Your work for the science working group NASA SOFIA, 1995, 1996. Are you present at the creation? Is this the earliest conversations leading to SOFIA?

ZMUIDZINAS: I first remember hearing at SOFIA as a graduate student. I remember during one of the observing runs on the Kuiper, while I was at NASA Ames, I was in the office of one of the people involved in the Kuiper program, and they had this little toy plastic model of a 747 with a telescope. Now, the telescope was in front of the wings like it was for Kuiper, whereas in SOFIA, it ended up being located behind the wings. It was an early version of the SOFIA concept. [Laugh] And that idea had been bouncing around since the time I was a graduate student, when people would talk about the idea of a bigger airborne observatory, and the people at NASA Ames especially were pushing for it. But it really was in the mid-90s where it really started to happen. By 1995, the Kuiper stopped flying, and the reason was to start saving money to put into the SOFIA program. Then, by 1997, I submitted a proposal to basically build a super-duper version of our Kuiper instrument for SOFIA, which was selected and was funded. I was there watching SOFIA get off the ground pretty much through the entire time.

ZIERLER: Then, why the mid-1990s, since it has this long history of being conceptualized before then?

ZMUIDZINAS: It all boils down to funding. You need a good mention in the decadal survey, but you also need NASA to actually decide it has the money. You may need Congress to approve funding. It just boils down to when the money actually starts to flow. That's what happened in SOFIA's case, it started to flow. As I mentioned, by 1997, they called for proposals for instruments. We were expecting to by flying on SOFIA four years later in 2001. Of course, that didn't happen.

ZIERLER: What did happen?

ZMUIDZINAS: Well, it took a long time for the airplane and its telescope to finally get built and for SOFIA to start doing science flights. I think that didn't really happen until 2009 or 2010. By that point, we had also been involved in the Herschel Space Observatory. This was due to Tom Phillips's efforts to try to get a space project going. The US, through NASA, ended up having a pretty significant participation in Herschel, and we at Caltech and JPL ended up building a fair bit of hardware for the instruments. In my own lab, we built the highest frequency superconducting tunnel junction mixer for the HIFI instrument, together with our JPL collaborators. There were lots of so-called local oscillator components that were supplied for HIFI, and Jamie Bock and Andrew Lange were involved in providing the bolometer detectors that were used in another one of the instruments, called SPIRE. Those detectors were also produced at the JPL Microdevices Lab and used a technology very similar to the detectors that flew on Planck, the cosmic microwave background mission. In fact, Planck and Herschel were launched together on the same Ariane rocket, so they were basically sister missions. There was a lot that was going on in preparation for Herschel and Planck in developing and building the flight hardware. We were deeply involved in that.

At the same time, we were funded to build this instrument for SOFIA. But the SOFIA project would chronically run into financial problems, and they would decide the only place to get money was to reduce the funding to the instrument groups. We were on a roller coaster ride. Some years, we had some funding, other years, it was sharply cut back. When they cut it back, our people would leave, and when SOFIA would again give us money, we no longer had the people we needed. It was a very painful and inefficient experience. So Herschel launched in 2009 and we started to see the data coming in from HIFI, but there was a near-death experience that happened there. The local oscillator system had a problem, and it wasn't clear if it was going to work. I'm blanking on what the problem actually was – maybe it was a power supply - but there was a redundant spare, which worked and saved the day, and we started to see the data coming in.

And it was beautiful, just spectacular. It was at that point that I realized that it didn't make a whole lot of sense for us to continue with the SOFIA instrument. The idea of the SOFIA instrument was to get going early, to be observing in 2001, and to have almost a decade of work before Herschel launched, and of course, it was the other way around, Herschel started getting data before SOFIA. That really diminished my personal interest in continuing with SOFIA. There was a review that was held about a year after Herschel launched where I said, "It doesn't make sense for us to finish this instrument, given what Herschel is producing. We can either stop, or we can try to make this instrument be something else that would make more sense."

ZIERLER: Because it was redundant?

ZMUIDZINAS: It was going to provide capabilities that were not as good as what we had on Herschel at the end of the day. It would've been great pre-Herschel, but post-Herschel, it wasn't that exciting.

ZIERLER: What made the difference for Herschel?

ZMUIDZINAS: First of all, with Herschel, you don't have to look through an atmosphere. Second, the telescope was 80 kelvin instead of 260 kelvin on SOFIA, so you had a colder telescope. Herschel's telescope was also somewhat larger than SOFIA, 3.5 meters vs 2.5 meters. Third, Herschel could observe all the time, whereas SOFIA, you had to take off, do some observations, and land. The duty cycle for gathering data was low in comparison to Herschel. If you didn't have an instrument whose capabilities were somehow different or better than what was on Herschel, it was just not going to be possible to compete. Our instrument was conceived with the idea that this was something we would be using for nearly a decade before Herschel. In 1997 when we wrote that proposal, that was the idea. We were being told, "Be ready to fly in 2001."

ZIERLER: When did the idea of establishing an observatory in Antarctica start? Generally, it's understood that this would be a great place, but when did those discussions start to get real?

ZMUIDZINAS: My awareness of all this started when I was a post-doc at Illinois. That was because my post-doc supervisor, Fred Lo, who I mentioned, was interested in getting a submillimeter astronomy program going at Illinois. He was talking to people, and one of the groups he talked to was the group at Bell Labs. By that time, Arno Penzias was out of the picture and doing other things, but Bob Wilson, who was a co-recipient of the Nobel Prize with Arno for the discovery of the microwave background, was still working in radio astronomy. He was actually a Caltech PhD in the early 60s. He was working in millimeter astronomy at Bell Labs, and he had these two younger scientists, Tony Stark, another Caltech alum, and John Bally. The three of them had a pretty active millimeter astronomy program. This was probably largely Tony's idea, although I don't know for sure, but they had an idea to build a submillimeter telescope at the South Pole. There was science happening at the South Pole. As a post-doc, I went to visit this group at Bell Labs in 1989.

During that visit, I sat in Tony Stark's car, he had a nice Porsche 911, and he drove us down to Delaware, the Bartol Research Institute, if I remember correctly, which was hosting a conference about astrophysics in Antarctica. I believe there, Tony presented this idea of building a small submillimeter telescope at the South Pole, which he called AST/RO, Antarctic Submillimeter Telescope/Remote Observatory. The idea was to put these new superconducting receivers behind a small dish and do submillimeter astronomy from the South Pole. Primarily, to study neutral atomic carbon. I think I talked about that as being part of my PhD thesis. Tony had the idea that with this telescope observing all the time from the South Pole, you could really start to map out the distribution of carbon in our galaxy, much in the same way that others were doing for carbon monoxide, sketching out the distribution of this atomic part of the dense interstellar medium in our galaxy. Fred Lo got involved in that, and they wrote a proposal to NSF. There was part of the project that was supposed to happen at Illinois, and had I stayed at Illinois as an assistant professor, that's one of the things I would've been doing.

But I didn't stay, I went to Caltech, which left Fred in a bit of a hole because he needed someone who could contribute the Illinois part of that project. And Fred himself was not an experimentalist. He ended up hiring a post-doc by the name of Greg Engargiola, who later ended up at Berkeley. Greg would come to visit me at Caltech, and I would teach him how to build these superconducting mixers. That's how this AST/RO telescope got its workhorse submillimeter receiver. It was basically a spinoff of the stuff we were doing on the Kuiper. That receiver ended up getting installed, and they ended up doing this program of observing atomic carbon at the South Pole. But I was, at that point, not very involved in it. I was just trying to help Greg Engargiola succeed in providing a receiver for this observatory. But I didn't participate much if at all in the science that came from that project. But then, Tony was interested in following up with a much larger telescope, something like a ten-meter telescope, so he started writing proposals to do that. In the meantime, at Caltech, I had been working closely with John Carlstrom, who's now a professor at University of Chicago, quite famous as a cosmic microwave background experimentalist. John was actually flying on the Kuiper with us, and he was doing projects both at Owens Valley and the CSO. He was an experimentalist like me, so we had a lot in common. We worked together a fair bit.

But John ended up leaving Caltech to go to University of Chicago, and one of the issues for him was the two-body problem. His spouse, Mary Silber, was offered a professorship at Northwestern, so in Chicago, they could both pursue their careers, and they ended up there. John was working with Tony Readhead here at Caltech on a microwave background project, which was, you could say, a follow-on to some of the work that John Carlstrom had started at Owens Valley, looking at the microwave background using interferometry. When he got to Chicago, John decided to do a sister project to Tony Readhead's project, but to do it at the South Pole. Tony Readhead's project, Cosmic Background Imager or CBI, went to Chile, and Steve Padin was really the technical guru behind it. John and his group at Chicago built something they called DASI, the Degree Angular Scale Interferometer, at the South Pole. This was post-COBE, so people were very interested in following up the COBE discovery of anisotropy of the microwave background and to start to resolve it to see what angular scales corresponded to the anisotropy.

So you had the two sister projects, Tony Readhead's going to Chile, and John's going to the South Pole. Tony Stark, meanwhile, is pushing for a large submillimeter telescope at the South Pole but was unsuccessful in making that project happen. Then, when John's microwave background project started ramping down, he was looking for new things to do, and he ended up joining forces with Tony Stark and basically taking over the concept of a large telescope at the South Pole, redirecting its science in a major way to really aim more at the microwave background. That's what turned into the South Pole Telescope, which is a ten-meter telescope at the South Pole. John hired Steve Padin from Caltech to go work at Chicago. So Steve is one of the real technical gurus behind the South Pole Telescope. That was how that project happened.

ZIERLER: To go back to the origins of the Herschel Observatory, were you involved or following closely the Infrared Space Observatory in the mid-1990s?

ZMUIDZINAS: As I mentioned, I was involved in hydrogen fluoride detection, but I wasn't involved in the instrumentation for that project. My involvement in the science was, I'd say, basically limited to this hydrogen fluoride story. Although, I was certainly looking at the papers coming out of that mission. But it wasn't my central focus at the time. I was thinking more about longer wavelengths and how to advance the technology of those wavelengths.

ZIERLER: Was it always assumed that Herschel would be an ESA project? Did it have to be an ESA project?

ZMUIDZINAS: Well, the story of Herschel is that, as I mentioned, in 1982, the Field Report recommended this Large Deployable Reflector. If you go back and look at the early articles that describe it, they basically show a ten-meter Leighton dish springing out of the cargo bay of a Space Shuttle. [Laugh] That image is in a 1977 paper by JPL authors Robert Powell and Al Hibbs, who was one of Feynman's few graduate students, and co-author of the famous Feynman and Hibbs book on path integrals. That was the initial concept, a telescope that was aimed at submillimeter wavelengths and maybe the long far-infrared, but not much shorter because Leighton's approach to building a telescope was really optimized for those longer wavelengths. It wasn't really necessarily how you would choose to build a telescope if you wanted to go shorter. But the scientists were interested in shorter wavelengths. Then, LDR ended up, over the years, especially in 1980s, trying to become an all-singing, all-dancing telescope that worked at quite short infrared wavelengths, and it just got out of hand. It was technically too difficult and too expensive, which is why it never happened.

Meanwhile, in Europe, with this idea of LDR in the United States starting to get some traction, in Europe the scientists got together and proposed something similar, which they called FIRST, I think a carefully chosen acronym. [Laugh] It was supposed to stand in contrast to LDR. But it stood for Far-InfraRed Space Telescope, if I remember correctly. Their idea was not to try to make it all-singing and all-dancing but to have a more restricted set of objectives and try to have a real project, instead of LDR, which never happened. Neither group was able to actually get their project off the ground. But what happened around 1993 or so was, the two sides got together, and some of the key people are people I know well, Charles Townes, Reinhard Genzel, and Tom Phillips. By that time, Reinhard had left Berkeley, he left in 1996, to become director of the Max Planck Institute in Garching, which is where he spent the remainder of his career. He was in Europe, and he was pushing for this project, which became Herschel, with Charles Townes at Berkeley and Tom Phillips here at Caltech.

They were some of the major players that got the European and US communities to come together and try to do a joint project. By the late 90s, it was really Tom Phillips who was pushing throughout this whole time to get NASA to actually join the project and start providing funding. NASA's participation in Herschel was largely due to Tom's efforts. He just worked tirelessly to do that. He would go to NASA meetings all the time to keep pushing. I remember he asked me to come with him to NASA headquarters for one of these meetings to go talk about NASA joining Herschel, and we took the red-eye flight from LAX and landed in Washington DC at 6 in the morning. By 8 in the morning, we were in the NASA headquarters offices, then later that afternoon, we were back in the airport flying home.

ZIERLER: Didn't anyone hear of Zoom yet? What happened? [Laugh]

ZMUIDZINAS: Tom was just tireless. He really deserves, I think, the lion's share of the credit for getting the US involved in Herschel.

ZIERLER: Switching gears, some institutional history and some questions on service work at Caltech. You were on the freshman admissions committee from '96 to '98. I'm curious what insight that gave you into how Caltech chooses, among an enormous applicant pool, who actually gets to come here. There are lots and lots of students who score perfectly on their SATs, who get great grades. Caltech has an abundance of richness in terms of who to select. What insight did you gain on what is hoped to be an ideal Caltech undergraduate?

ZMUIDZINAS: My first reaction was, boy, was I sure glad that I had sent in my application 20 years earlier.

ZIERLER: That's the joke, you'd never get in today, right?

ZMUIDZINAS: Never get in. It was clear. That's spot-on, what you're saying. It was, for me, maybe even a little depressing to read all these fabulous applications, to see all this talent, these young minds aspiring to work in science, engineering, math and just not being able to really consider most of them. That, to me, was a little depressing. The question was, how do you decide who to admit? There were some spectacular applications from people who were obviously going to get in no matter where they applied. They were off-the-charts kinds of people. That's always true. My experience at Caltech is that no matter how smart you are, there's someone who's just way smarter than you. [Laugh] That's just a fact of life, and that's OK. There were a few of those people who were just way out on the tail. But they weren't going to fill up the class. As you started to consider filling up the class, there were a lot of applicants to choose from. Arriving at a decision as far as who to admit and to not admit was very difficult. I found it actually discouraging in the sense that we would see applicants who were the best students at their high schools, probably by a significant margin, and yet were not going to measure up to the standard of the admitted class. And that was a little depressing.

ZIERLER: I wonder if one of the limiting factors that made selection a little easier–I'm always interested that HSS really goes back to the founding vision of Hale, Millikan, and that generation who emphasized that, yes, this is an engineering and science school, but we want our undergraduates to be worldly, well-read, to have an appreciation of what's happening in the world so that they're productive members of society. One of the themes I hear over and over from HSS faculty is the pleasure they get in students who obviously did not come here for history and English but for math and science, but because of the kinds of students Caltech admits, they want to be in those classes in HSS. They're not just classes to tick off the box. I wonder if that was a useful limiting factor in making these difficult decisions on selection.

ZMUIDZINAS: Certainly, you look for breadth, not just in academics but in other areas. Extracurricular activities, whether it's music, sports, things like that. The idea that you want people who have a broader understanding and appreciation of the world and of life than just a very narrow focus on math and science, that is a good way to make decisions regarding admission. But one of the things that is clear is that not all high school students have the same opportunity to pursue those kinds of things. In reading these applications, I'd ask myself the question, what opportunities were available to them that they didn't take advantage of but could've? I found that a useful question to ask. If I saw a student who may not have been doing all the same things the other applicants were doing but had maximized what was available to them, were trying to take in everything that was in front of them, that was the kind of student I liked to see. And yet, any number of them just weren't going to be competitive. That's when it was discouraging. But Caltech is very fortunate to attract this kind of candidate pool and admit students who are very good. Life is not just about math and science. I think the Admissions Committee is correct to make sure that we admit students who are broader than just that. I think that's a good idea.

ZIERLER: Thinking about students within the context of the opportunities available to them, in the mid to late 1990s, was anyone at Caltech talking about diversity, about the importance of admitting students of color, of having more women undergraduates? Was that in conversation at that point?

ZMUIDZINAS: Absolutely. And already, by the late 1990s, Caltech was a very different place than the Caltech I attended in the late 70s. There were far more women, for example. And the numbers were dramatically different from when I was a student. One of the people who really made a hard push in that direction was Geoff Blake. He served as the chair of the Admissions Committee. I don't remember the exact years, but it was around that time, late 90s, early 2000s. He made a real effort to increase the number of women being admitted. Of course, diversity is broader than that. I'd say that my recollection of those times on the committee, it was the fraction of women that was front-and-center in terms of diversity. That seemed to be problem number one to get solved. I think since then, Caltech is in a much better place. Of course, we haven't solved all our problems, but there's been progress. Thinking back to the Caltech of the late 70s to what it is today, the progress is dramatic.

ZIERLER: Because you've also served on the graduate admissions committee, it's simply a unique opportunity to ask, what are those transferable values that you apply when selected for undergraduates that also work for graduate students, and then what are unique variables that you're going to look at for potential graduate students?

ZMUIDZINAS: For admission to graduate school, you're asking the question, "Is this a person who's going to be successful in research?" You're really looking for evidence that can help you answer that question. Getting good grades in your courses is important but not enough. You're looking for research experiences, hints of creativity, things like that. Graduate admissions is, I'd say, really highly focused on trying to understand the research potential of a candidate. With undergraduates, of course, it's pretty early to be doing that. Nonetheless, when you read the undergraduate applications, freshman admissions, you're also looking for that spark. What have they done that is unusual or different? It's not just participating in the science fair, it's something that they've created themselves, that they've pursued themselves, something unusual or different. Of course, it's a sign that they truly are interested in math and science as opposed to just being something that they've been told they should try to pursue. It's very early to be looking for that at the freshman level, but that is something that's common between the two processes.

ZIERLER: A much more focused question. For you, when you're thinking about graduate students to join your research group, when are you excited by a potential student's narrowness in their interests? In other words, this is what they want to do, and you're the guy to do it with, and that all sounds great. And when might that give you pause because you want to emphasize breadth, even at the graduate level among your students?

ZMUIDZINAS: I think what I would say is that I view myself as being involved in experimental physics, so I'm interested in graduate students who want to do experimental work. It doesn't really matter very much what kind of experimental work they're interested in doing or what their experiences in that area have been. It helps if perhaps they've been in a lab that does things similar to what happens in our group, but it's not essential. It gives them a little bit of a leg up, but it's really not something that persists much more than a year, I would say, into their graduate career. I don't have a very narrow filter for graduate students. As long as a student is interested in experimental work, has some capacity to do it, but also has a reasonably good understanding of physics on the theory side, they're going to be fine. Yes, if there's a student who has been in a superconducting detector group at Berkeley, has been doing the same kinds of things for three years, and they can come in and be immediately useful in a lab, that's fine. But that's not, in my view, a necessary condition. I've taken students with quite a wide range of backgrounds. Also, the projects that students do can be quite varied. Some students really focus on the device physics side. Some students are involved in bringing an instrument to completion and doing astronomy with it at a telescope. There's a wide range of experiences that students have, and it's not one-size-fits-all.

ZIERLER: Serving on the committee that reviewed proposals for the President's Fund. At this time, 1997, David Baltimore was brought in, an eminent biologist. The Biology Initiative was a big thing happening on campus at that point. Did that register with you, that there was this specific push in biology at that point?

ZMUIDZINAS: The President's Fund was a program to support joint projects between campus and JPL. To be honest, I forget the funding mechanism for it, but it almost certainly derived from the prime contract that Caltech has with NASA to operate JPL, and there was probably some provision in the prime contract that allocated these funds for that purpose. We were seeing proposals for collaborations between Caltech scientists and JPL scientists. I'd say that was probably my first experience really getting out into the wider world of science that was happening at Caltech and JPL as opposed to just astrophysics and astronomy. To be honest, I wouldn't remember if there were any biology-related proposals. [Laugh] I'm sure there were. I'm sure that A, I was not asked to be a primary reviewer, and B, I probably understood less than 50% of the contents of the discussion. [Laugh] But there were many other things. There were lots of earth science proposals, engineering proposals, technology, all kinds of stuff, and it was a lot of fun.

ZIERLER: Did that work lead you to serving on JPL's Administrative Committee in 1998?

ZMUIDZINAS: By then, I had had a close collaboration with people at JPL and had a number of joint projects. I was viewed, I suppose, at the time, as being one of the Caltech faculty who had closer ties with JPL, so I suspect that's why I was asked to do that. Although, I don't remember much from that committee. I don't remember being particularly active.

ZIERLER: Did you have a front-row seat to the high-profile mission failures at JPL in the late 1990s?

ZMUIDZINAS: Absolutely. There was the Mars Polar Lander. I remember my wife and I came to JPL in the evening to watch the landing. We were seated in a conference room and were told that there were several members of Congress in the same room. It was, I guess, a quasi-VIP room. The real VIPs were, I'm sure, somewhere else. But that was a very depressing night.

ZIERLER: What about the Mars Climate Orbiter? Did you have a similar experience with that?

ZMUIDZINAS: I don't remember the Climate Orbiter to be honest. I don't have the same recollection of sitting at JPL for that.

ZIERLER: Did you have interaction with Ed Stone much during this period?

ZMUIDZINAS: I would say not that much. I would see Ed, mostly when he had time to be on campus, and often, that was on Saturday because he was JPL director at the time. But really, there was nothing we worked on together in common during those years. I'd see him at faculty meetings, for example. We would wave hi, but that was about it.

ZIERLER: What was your sense of the role of the faster, better, cheaper ethos at NASA in terms of being a contributing factor to these failures in the late 1990s?

ZMUIDZINAS: That's a really interesting question. I'm pretty sure I'm not the authority on this, having watched it only from a distance. But I've read a few things about this, and there are articles that try to assess the faster, better, cheaper era in retrospect, and having had a little bit of distance from it, try to take a little more rational look at the pluses and minuses. Of course, when you have a gut-punch failure like the Polar Lander, it's tough to stay the course. NASA felt that they absolutely needed to change direction and couldn't continue along that path. But the assessments I've read are that actually, faster, better, cheaper was reasonably successful. There is, apparently, a Keck Institute for Space Studies report, which I'm not going to remember the exact name of, but it's something about doing Mars missions, in addition to sample return, with a faster cadence for less money, less expensive missions more often and more quickly to supplement the sample return. Apparently, there's a Keck Institute for Space Studies report on this, and in the appendix of the report, there's an analysis of faster, better, cheaper. Because a lot of what this report is advocating sounds a lot like returning to faster, better, cheaper. Rob Manning (BS '82) was interviewed, Chief Engineer at JPL, and he was deeply involved in Mars Pathfinder.

I read a quote from Rob which said that what was happening in the faster, better, cheaper era was that each successive mission was becoming more and more complex for the same or smaller budget, and with the experience of the project team members being reduced every step along the way. Things were getting harder with a less-experienced team and no more money, if even that much. I think Rob's view is that it was going in the wrong direction. It wasn't a steady-state situation, it was getting untenable, and that's why we had these failures. I personally think that it would be great if JPL and NASA could figure out how to be less risk-averse, how to do smaller missions, do them for a lot less money, and do them a lot more frequently. It seems inevitable that that's the way things are going to go with SpaceX being able to drop launch costs substantially, recovering the boosters by landing them, being able to reuse them. All of that is driving launch costs down. The cost of the payload you put on top of the booster has to have some relationship to the cost of the booster. If the launch costs are dropping, you better figure out how to build payloads whose cost is not orders of magnitude more than the rocket you're putting them on. It just seems logical to me that that should happen. I think there will be a pressure to head in that direction over the coming years.

ZIERLER: To return to the missions, with SOFIA, was it always conceptualized to be a collaboration with the Germans?

ZMUIDZINAS: As long as I can remember, Germany was part of that.

ZIERLER: Why Germany specifically?

ZMUIDZINAS: I think partly because there were scientists in Germany who were interested in infrared and far-infrared astronomy. When I was a graduate student, our tiny Berkeley group of three people was competing, basically, with another larger group from the Max Planck Institute for Radio Astronomy in Bonn, Germany, a group led by Hans-Peter Röser, and they built an instrument that was much like ours, same components, far-infrared laser, same type of semiconductor mixer, etc. And they were pursuing airborne astronomy on the Kuiper. On our honeymoon in Europe in 1985, while I was still a grad student, my wife and I stopped in Bonn and were invited to dinner with Hans-Peter and his wife at their home. Hans-Peter Röser later became director of the DLR Institute in East Berlin (Adlershof) after the fall of the Wall, and later moved to the University of Stuttgart and helped found the SOFIA institute there. He was a central figure in getting Germany involved in SOFIA. And there were others. Reinhard Genzel's group ended up building an instrument for SOFIA. It was a descendant of an instrument that was built in Charles Townes's group, which Reinhard used when he was an assistant professor there, then later extended and improved while he was at Berkeley. I don't know to what extent Reinhard pushed for Germany to be involved in SOFIA, but I suspect he certainly helped.

ZIERLER: Of course, the obvious connections are there from SOFIA to the Kuiper Airborne Observatory, but just going back further, when are the first discussions about putting a telescope in a 747 or a large civilian aircraft? How far back do those discussions go?

ZMUIDZINAS: Well, I mentioned that in the early 80s, there was a toy model of a 747 with a telescope. We were already then flying on the Kuiper, which was a C-141 cargo jet, four-engine. But there was a predecessor to that, which was called the Lear Jet Observatory. The telescope was fairly small, but to my knowledge, that was the first stratospheric airborne observatory. I don't know the detailed history of exactly when the Lear Jet started flying. It might've been already by the late 60s, 1970 or so (1968). One of the key people involved in the Lear Jet was Frank Low, who was an infrared astronomy pioneer at the University of Arizona. Frank Low, circa 1960, invented a new kind of detector, which was a bolometer. A bolometer's a device that takes radiation, turns it into heat, and essentially uses a thermometer to measure the temperature change. Radiation comes in, the device heats up, and the thermometer measures the response. To make a bolometer sensitive, it has to be cold, so Frank had the idea of cooling his bolometer to liquid helium temperature, four degrees Kelvin, then using a piece of germanium semiconductor as a thermistor, as the device that measures the temperature change, and in so doing, was able to build infrared detectors that were very sensitive for their day.

He used those detectors to pioneer infrared astronomy. He first went to the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, and started doing millimeter-wave astronomy with his detectors. That was probably one of the inputs that got Bob Leighton interested in the field. There was eventually a telescope that NRAO built in Arizona (1968), on Kitt Peak, which I believe was called the 36-Foot Telescope, a millimeter-wave telescope that was supposed to be a telescope that Frank Low would use, but I think he left NRAO and ended up at University of Arizona. It was around then that I believe he got involved in airborne astronomy (in 1965). He was either the first or certainly one of the very early users of the Lear Jet Observatory in the early 70s. I don't believe Frank ever had an instrument on the Kuiper, although I'm not the definitive source for that. But people like that were the people who led to the creation of airborne astronomy.

ZIERLER: Just a general question about airborne astronomy. I'm assuming this is obviously a very dynamic environment. It's loud, it's windy, it's noisy. That must create a lot of noise in the signal. What noise dampening techniques need to be developed in order for these telescopes to produce worthwhile data?

ZMUIDZINAS: Problem number one is keeping the telescope pointed at the object you're interested in as the airplane is flying. What that means is, you want to prevent the airplane from being able to twist and turn the telescope, from what physicists would say is applying any torques to the telescope, disturbances that would cause the telescope to change its orientation. The entire telescope floats on a fairly large spherical air bearing. That air bearing is the interface between the telescope and the airplane. Even though the airplane might be moving, it may be rolling, pitching, yawing, whatever terminology they use, that doesn't end up leading to the telescope doing the same thing. The telescope has a pretty large moment of inertia. It's not so easy to twist and turn. That's the first way.

ZIERLER: An air bearing means what?

ZMUIDZINAS: That you have, basically, a giant steel ball, which is surrounded by a giant steel cavity whose diameter is only slightly larger than the steel ball. The telescope is attached to the steel ball, and the cavity is attached to the plane. Then, there are air jets, little holes, and there's compressed air being blown in so that the whole telescope is riding on a film of air.

ZIERLER: The jets that blast air are responding to the plane's movement?

ZMUIDZINAS: No, they're causing the sphere to basically float inside the cavity without touching it, so you don't have any friction. It's a nearly frictionless bearing. I have to admit, in SOFIA, it may be a hydraulic bearing, I don't remember (yes – a hydrostatic bearing). But the idea is to have a very low-friction connection between the telescope and the airplane. That's step number one. Step two is, you don't want the telescope to be vibrating. You don't want vibrations from the airplane to be transmitted to the telescope. So there are essentially big shock absorbers. This bearing is mounted to the airplane with big shock absorbers to prevent vibrations from being transmitted. Then, all of this is fine, but to keep the telescope pointed, it still requires actively adjusting and controlling the pointing of the telescope. On the Kuiper, there was a system where there was a television camera that would look through a small telescope mounted to the side of the big telescope, and it would look at the star field, then a computer would take a look at the image from the television camera, and you would choose a guide star. The computer would find the location of that star, then it would calculate how that star was moving, and it would send signals to these big electromagnetic torque motors that were used to move the telescope back into the correct position. As this feedback loop was running, the star would be locked in the location that you wanted so that the telescope was pointed at the object you wanted. Every so often, as you're flying along, you hit a patch of turbulence, then things go haywire, the telescope goes out of lock, you have to stop, reacquire, and start observing again. It took a lot of clever engineering to make this work.

ZIERLER: I wonder if, when you talked about shock absorption, there was any collaboration with LIGO, who obviously had their own concerns with isolating vibrations.

ZMUIDZINAS: Certainly, LIGO has to do vibration isolation at a level far beyond what you need for the plane, and Kuiper was built before LIGO. I don't think that LIGO would've learned much from examining what Kuiper did that would've been useful to them because their problem was much more severe. But you could say that the ideas involved are not dissimilar. You're trying to make what an engineer would call a low-pass filter for vibrations, something that does not transmit vibrations that are faster than some level. Instead, it gets rid of those, it attenuates or damps those.

ZIERLER: In what ways does airborne astronomy split the difference in terms of the competing factors in land-based and space-based astronomy, whereby in land, you can go big, but you have to go through the atmosphere, and in space, you don't have an atmosphere to go through, but you have to get it up there, so it's limited by its size?

ZMUIDZINAS: The idea of airborne astronomy is that access is much more frequent. The airplane takes off and lands, and it does that many times a year. Whereas in space you put it up, and whatever you put up is what you're stuck with. The philosophy, and it was certainly true in the Kuiper era, was that every time you flew, your instrument could be improved. Or you could build a new instrument and put it on. You could learn from your experience flying. You could figure out what it was in your instrument that was maybe not performing at the level you'd like. You could keep improving it. That doesn't work for space. Certainly, that is standard practice for ground-based observatories, although less so for the large, expensive observatories than the smaller observatories, like the Caltech Submillimeter Observatory. Airborne astronomy certainly is an intermediate point between the two extremes, but I'd say that for the Kuiper, this was much more true than it ended up being for SOFIA. The SOFIA instruments are bigger and larger. The amount of oversight involved in building an instrument, especially with regard to airworthiness concerns, increased dramatically for SOFIA. The size of the instrument and the complexity, along with the much higher level of scrutiny on instrument designs, led to SOFIA instruments being far more expensive than on the Kuiper.

As a result, the instrumentation on SOFIA has not followed the practice that was true for the Kuiper, where the instruments were pretty dynamic. Lots of new instruments coming on, constantly being improved. For SOFIA, the instruments that were chosen back in 1997 are still the only instruments flying. I believe that's a true statement. Here we are in 2022, and 25 years ago, the selections were made. The instruments have received various upgrades along the way, but in my view, not nearly as frequently as would've been desirable. In particular, with some exceptions, SOFIA has not really proven to be a very useful platform for technology development and demonstration. That's one of the things you can hope to do on an airborne platform that you have ready access to, that you can replace the instruments and change the instruments. But because of those factors, and to some degree, due to budget limitations, SOFIA has not been, by and large, a platform for technology advancement and demonstration the way I would've liked to see.

ZIERLER: What about what I assume is an obvious asset of airborne astronomy, whereby the plane is not limited by one hemisphere or another and can travel anywhere in the globe? How important is that for the kind of astronomy that Herschel was designed to do?

ZMUIDZINAS: My wife, Vilia, who you see in the background, would relate to you a painful experience of me missing her sister's wedding because in 1994, if my memory serves, there was this famous comet crash on Jupiter (Shoemaker-Levy 9). There was a scientist at JPL, Peter Wannier, who actually had been an assistant professor at Caltech in the 1970s and worked with people like Mike Werner, Bob Leighton, and so on. And he worked at Owens Valley as well. And, he is the ex-husband of Louise Saffman, who interviewed me when I applied to Caltech from high school. But I mentioned interstellar water and the ability of our instrument to look for this oxygen-18 flavor of water. You have this comet that's going to crash into Jupiter. The comet, to the first order, is just a big, dirty snowball. Peter thought it might be interesting to see if we could detect water vapor in Jupiter's atmosphere resulting from this comet crash. In order to do that, the flights would need to be done from Australia. This is getting to your question about being able to go to different places on the globe to catch astronomical events. We did that. I told my wife I wasn't coming to the wedding, and I haven't lived it down since.

ZIERLER: [Laugh] I hope you got some good science out of it at least.

ZMUIDZINAS: We failed to detect water. [Laugh] But the comet observations were only part of what we could do. It only occupied no more than half of the flight, so we were able to get other science done. And it was a lot of fun, and we got to do a three- or four-day tour of the Australian coast south of Melbourne. And to prepare for these flights, because we were going up to 45,000 feet, we joined the U-2 and SR-71 pilots at Beale Air Force Base for high-altitude training. It was all good fun.

ZIERLER: Last question for today, we'll end on an administrative question. I'm curious what your experiences were coming in as an assistant professor and whatever advice you got or what you understood about the culture of promotion at Caltech. In other words, where at some universities, it's very obvious that an assistant professor is a glorified post-doc, where there really should not be any expectation of promotion. Did you feel like you were given all of the tools and support in order to succeed because the assumption was, if you're doing good work, you will be promoted? And going from associate to full professor, is that more pro forma at that point, or is there a specific thing that you're doing for which the full professorship is being recognized?

ZMUIDZINAS: As I mentioned, my post-doc advisor, Fred Lo, did not receive tenure at Caltech, so I knew it wasn't a sure thing. On the other hand, in speaking to my colleagues, in particular, I remember a conversation with Geoff Blake, who maybe came a year or two before me as an assistant professor to Caltech, where he described his understanding that at Caltech, it was, at least in principle, possible to get tenure, whereas at a place like Harvard, it just wasn't. It just never happened. [Laugh] You could look at the track record of assistant professors before you, and certainly not all of them got tenure, as I well knew, but some of them had. My understanding coming into the position was that there were certainly no guarantees. Far from that, it was going to be hard work and more than a bit of luck to be able to get tenure, but that it wasn't ruled out, you had a shot.

ZIERLER: What about the resources, the way that Caltech invests in its junior faculty so that success is more likely than it otherwise might be?

ZMUIDZINAS: It's hard to compare, of course, because individuals are different, their needs are different, the fields are different, fields evolve, and what it takes to put together a successful research effort in a particular field at a particular time can change quite a lot over time. When I started at Caltech, I received $200,000 of startup funding, which today seems like a paltry amount. [Laugh] But for me, it was enough. I received a lab, which was full of junk that nobody had used in quite a while, and therefore, it was the repository of all the old equipment people didn't want. It was like a storage closet of everybody's junk. It had a hatch to the roof, which to my understanding, was used by Bob Leighton–it was on the fourth floor of Downs–to test out a prototype of what became Big Bear Solar Observatory. My understanding was that Bob would flood the roof, and the building was designed to accommodate this, to simulate having a telescope in the middle of a lake. I had this hatch, and the only bad part about that was, after however many years since it'd last been used by Bob, it had started leaking when it rained, which I discovered after a rain storm with water all over my new optical table. It was a lot of work to get that lab into shape. I didn't have any help, any students or post-docs. The first person who joined my group was a technician I hired, an electronics technician Dave Miller, then I started adding students and post-docs as I started getting grants. But I personally cleaned out that lab, got all the lab furniture installed, equipped it with all the electronics instrumentation, built the first version of the receiver we used to test the devices that flew on the Kuiper. I was basically a one-man show, at least in the first year, before I started getting some help. But it wasn't anything I wasn't used to. At Berkeley, I was in a small group, and we did everything ourselves. At Illinois, I showed up, and there was nobody to help. I set up a new lab there, worked with a grad student (Fred Sharifi) to set up vacuum equipment for making these tunnel junctions, I designed and built electronics. This was just what I did. I felt like I was just continuing doing what I did. ZIERLER: I wonder if that was part of Tom Phillips's calculus, he knew this about you. ZMUIDZINAS: Being an experimental scientist meant that's what you did, you built stuff and tested it. I would say this startup funding I received from Caltech was easily sufficient for me to get going in this field at the time. It allowed me to get the first tests done of these new devices we were making at the Microdevices Lab. It allowed me to win a proposal for building an instrument for the Kuiper. It allowed me to win NASA proposals for developing advanced versions of the detectors. Once you start to have some success, you can keep having success. From the time I showed up at Caltech to the last time I wrote a proposal for experimental research funding, which was in 2015, I never had a single proposal rejected. That$200,000 was enough. [Laugh]

ZIERLER: The tail end of that question regarded the promotion from associate to full. Was your understanding that that's more of a steady progress, you're continuing to do good work, and this is something that happens? Or is that another dramatic moment where there's something big that you do, and you're specifically being recognized in this way?

ZMUIDZINAS: These days, I don't know that there's much distinction anymore. Either you have tenure, or you don't. I certainly thought it was a big step. That was my perception, looking around the department at who was full professor, who was associate, and so on. It seemed to me a pretty big step. The division chair at the time, Tom Tombrello, circa 2000, told me to start getting ready for the promotion. I told him, "Hold on. I'm not ready. There are several important papers I want to finish before putting the package together." He laughed at me and thought I was being ridiculous. But I felt that it would make me feel good to have that work completed before going through the process. In some ways, it was motivation for me to finish that work before submitting, so I did.

ZIERLER: What were the papers?

ZMUIDZINAS: One of them wasn't so much a paper as it was a manuscript that we used to start working on a new kind of detector, the so-called microwave kinetic inductance detectors, which I had co-invented with my JPL collaborator, Rick LeDuc, in June of 1999. It was an idea I thought had a lot of promise, and I wanted to flesh it out and have this idea be part of the package I submitted for full professorship. There were probably a few other papers I was hoping to complete, and I'm thinking I may not have completed at least one of them until around 2002, 2003. There was a paper I had been working on that was partially done, and I think I didn't finish that one and get it published until 2003, but I may have included an early manuscript in that promotion package. But that was a paper on understanding in more detail how the kinds of instrument concepts and methods used in radio astronomy can translate or not to shorter wavelengths, to visible-wavelength astronomy. The techniques used in radio astronomy are quite different than are used in optical astronomy. In the submillimeter wavelength range, we borrow from both ends of the spectrum. We borrow ideas from optical astronomy, we borrow ideas from radio astronomy, we mix and match, we use everything.

But depending on what you're trying to do, what kind of instrument you're trying to build, if you're going to space or it's a ground-based instrument, those factors can play into which techniques work well and work less well. Fundamentally, it boils down to quantum mechanics and the statistics of photon arrivals, things like that. This was a topic I'd been running into. In my early days in graduate school, I remember taking a course from Reinhard Genzel where these topics were getting discussed, there were papers on similar things, and none of them left me with a very satisfactory feeling that all the fundamental issues had been sorted out and understood, at least to my satisfaction. This was my attempt to sort it all out and lay it out clearly in a way that I could understand. That paper was finally published in 2003.

ZIERLER: It sounds like you're not discounting the role of intuition in making these decisions, to some degree.

ZMUIDZINAS: Certainly, when you build an instrument, there are a lot of important factors, a lot of practical decisions you have to make. Availability of various components and technologies, how ready they are to be used in an instrument, all kinds of things. But if you think about the principle of how the measurement is being made, the fundamental architecture of the instrument, that's when these fundamental considerations come in. And even to this day, this stuff comes up. I mentioned this far-infrared probe that's going to have a cold four-kelvin telescope, if it ends up going. There was a larger mission study, the flagship-class mission concept called the Origin Space Telescope, a six-meter, four-kelvin telescope. And that's where these things come up. You have the radio-style instruments that some group of scientists are advocating, you have the optical-style instruments that others are advocating, and they're not equivalent. On a cold telescope like that in space, the radio-style instruments have a big disadvantage. That's something that, over the course of my career, has come up time and time again and I've had to work through and understand. There's a new generation of scientists coming up, and they're faced with the same questions and problems, and they need to understand it. [Laugh]

ZIERLER: On that note, we'll pick up next time early 2000s going forward.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Tuesday, March 29, 2022. I am delighted to be back with Professor Jonas Zmuidzinas. Jonas, it's great to be with you again. Thank you for joining me.

ZMUIDZINAS: Thank you, David. Great to be with you.

ZIERLER: Today, I'd like to start in the late 1990s. Your work with the Antarctic Submillimeter Telescope and Remote Observatory, how well integrated was that in your overall research agenda at that point?

ZMUIDZINAS: It was, I'd say, a project that I was assisting out of a sense of obligation to my post-doctoral advisor, Fred Lo. When I was at University of Illinois in the late 80s, he got involved in that project with a couple of people at Bell Labs I mentioned before, Tony Stark, John Bally, Bob Wilson. In the early to mid-90s, I was helping that project, particularly a post-doc who followed me at Illinois, Greg Engargiola, provide the receiver for that telescope using the devices we had been developing for the Kuiper using the JPL Microdevices Lab. It was a side project for me. I was trying to make sure that Fred and Greg at University of Illinois could be successful in fulfilling their commitments to that project. It wasn't so much something I was personally involved in scientifically.

ZIERLER: Is there something special about Antarctica in the way that it contributes to submillimeter astronomy?

ZMUIDZINAS: It was recognized for quite some time as being an excellent site in terms of the characteristics of the atmosphere. Of course, it's very cold there, and the atmosphere is quite dry as a result. Water vapor in the atmosphere is the thing we worry about the most at submillimeter wavelengths, so it's a good site to do millimeter and submillimeter astronomy from. The atmosphere is also very stable because you don't have the 24-hour diurnal cycle, the days and nights last six months. That eventually is what led to the Ten-Meter South Pole Telescope being built there.

ZIERLER: It makes me think, with all of the political problems in Hawaii, obviously none would exist like that in Antarctica. Is it feasible to build an ELT in Antarctica?

ZMUIDZINAS: It certainly is feasible. The question is, what would it cost? [Laugh] It's a challenging place to work. Building a ten-meter submillimeter telescope at the South Pole was quite an undertaking. You can expect that both construction and operations costs at a site like the South Pole are going to be substantially higher than a site like Hawaii, where it's quite a bit easier to get to. Hawaii, Mauna Kea, you can drive a truck to the summit.

ZIERLER: If they'll let you. [Laugh]

ZMUIDZINAS: The South Pole, you have to fly in. There's a big difference in terms of access. And you can't fly in all the time. There's limited time during the year. Once the South Pole closes for the winter, the people there are stuck there until it reopens for a period of months.

ZIERLER: Was the AST/RO supported by NSF?

ZMUIDZINAS: Yes. There's an office at the NSF, the Office of Polar Programs, that supports these various research activities at the Pole. My understanding is they supported and continue to support the South Pole Telescope.

ZIERLER: Given that you weren't so involved scientifically, what does it say just in terms of its relation to what you were interested or lack thereof at the time? What is the larger story there?

ZMUIDZINAS: I had many other opportunities, so we were quite busy up until the mid-90s flying on the Kuiper Airborne Observatory with our instrument, then we successfully proposed to build the instrument for the successor, SOFIA, and I think I told you how that turned out. But nonetheless, that was a project that was keeping us busy. Then, Herschel, by the later 90s, in '98 or '99, started to get very busy. During the whole time, we had very good access to the Caltech Submillimeter Observatory on Mauna Kea. My focus was on those opportunities and exploiting them. This AST/RO project at the South Pole was, you could say, not the highest on my list of priorities of things to be spending time on, given everything else on my plate.

ZIERLER: 25, 30 years ago, your work on Mauna Kea at that point, because so many of the challenges that TMT is facing right now are because of historic grievances that the native peoples of Hawaii have expressed, did that register with you at the time? Were people concerned about that? Were indigenous people making their concerns heard, or was that a nonissue as far as you were aware?

ZMUIDZINAS: In the 1990s, and in fact, through most of the time I was involved with the CSO, these issues were expressing themselves in various ways, but not really having a significant impact on the CSO itself. There were other facilities that, I'd say, felt a little more of that. There was an attempt to build these outrigger telescopes to work with the Keck Observatory to do interferometry. That ended up not proceeding, in 2006, partly as a result of opposition from the native Hawaiians. We were certainly hearing about those issues and those politics, but it wasn't something that was really affecting the CSO in any significant way. That remained true almost through the entirety of the operational life of the CSO. But when TMT attempted to start construction, there were a couple of times when protestors actually blocked access to the summit with their protests in the mid-2010s. I think in 2015, there was such an episode, if I remember correctly. In fact, the last time I was at the CSO for observing, in late May 2015, was a couple of months after one of the protests where the roads were blocked. That was really the only time when there was an impact on the CSO.

ZIERLER: Did that give you pause? I know the conceptualization of the TMT is still a ways off. But did you ever think in those early days that if there would be a major new project for Mauna Kea, that these problems would crop up?

ZMUIDZINAS: Absolutely. I think it was pretty clear, especially given the experience with the Keck outriggers, that this was no longer an issue that could be neglected. I wasn't very close to the politics surrounding this issue until fairly recently, when, as COO director, I was asked to serve on the board for the TMT International Observatory, and I really started to hear about this issue in quite a lot of depth. But that's only been in the last four years or so.

ZIERLER: This is going to be a big chicken and the egg question in the turn of the century, late 1990s into the 2000s. On the observing side, you're developing an interest in distant, high-red-shift submillimeter galaxies. On the other, you want to build these detector arrays, these MKIDs, that make that possible. Which precipitates the other? How did that work for you?

ZMUIDZINAS: Actually, in the early 90s, around '93, I first started thinking about building detector arrays. I was reading papers about the possibility of finding galaxies in the submillimeter. I had a postdoc, Andre Clapp from Paul Richards' group, who was interested in these topics. Some of those papers were written by Andrew Blain, who ended up becoming an assistant professor at Caltech later on but is no longer here. But the interest in the subject goes all the way back to the 1960s, when Frank Low, whose name I mentioned, invented the liquid helium-cooled germanium bolometer and pioneered infrared astronomy. He started detecting galaxies that were bright at long infrared wavelengths in the 1960s, and he wrote a paper (with Wallace Tucker) in Physical Review Letters in '68 or '69 (1968) which basically said the following. "If I've managed to detect a couple of these in the nearby universe, it can't be by accident. The universe must be filled with these things." He made a giant extrapolation, saying, "The little bit we've learned from measuring a few of these nearby examples, let's imagine a universe filled with these things. What would that mean?" It was a rather bold prediction. But then, there were follow-up papers and attempts to detect emissions from these galaxies in various ways, there were rocket experiments at Cornell. Andrew Lange, for his PhD thesis, worked on a rocket experiment in this area. There were a lot of false starts, and nothing definitive really was discovered until COBE, the Cosmic Background Explorer NASA satellite in the '96, '97 timeframe.

There were several papers that came out with a definitive detection, not of individual galaxies, but by the combined far infrared submillimeter emission from the entire population of galaxies throughout the universe, showing that Frank Low's prediction back in 1968 actually had something to it. Of course, Frank didn't have all the information to do the prediction correctly, but he got surprisingly close to the right answer nonetheless. He has a figure in his paper like the one I described earlier, with intensity or energy on the vertical axis and wavelength on the horizontal axis, showing the three bumps due to the cosmic microwave background at millimeter wavelengths, from redshifted starlight in the optical and near-infared, and a third bump, the far-infrared bump, in between. And the starlight and far-infrared bumps in his figure are about the same height, representing the same amount of energy, which is basically what COBE found. There were things happening like that. At millimeter wavelengths, people were studying galaxies in molecular emission lines like carbon monoxide and other molecules like HCN. People were finding that these infrared bright galaxies often could have a lot of molecular gas, that much of it was quite dense, and that there was a lot of star formation happening in these galaxies. And people were pushing to try to observe more distant examples of these. There was a famous paper by Brown and Vanden Bout (1992), where they claimed detection of carbon monoxide in a fairly distant galaxy that was discovered by the IRAS satellite (IRAS 10214 at redshift 2.2). IRAS was a JPL/Caltech/NASA project that Gary Neugebauer and Tom Soifer were involved in.

I think I might've told you about that trip to Melbourne, Australia with the Kuiper to go observe the comet crash on Jupiter that caused me to miss my sister-in-law's wedding in 1994. On that same trip, if memory serves, Tom Soifer, now a retired former division chair and professor, had written a proposal to use our instrument on the Kuiper to try to detect the emission line of ionized carbon from this distant IRAS galaxy, IRAS 10214. Of course, with the small Kuiper Telescope, this was going to be challenging, and we didn't detect anything. But it's an example that already, in the mid-90s, people were pushing to see if you could explore the distant universe in the submillimeter and millimeter. I'd say by 1993, I was thinking about how to build a camera to just make images of the submillimeter and try to identify these galaxies without needing other types of measurements to do it. I started thinking about various kinds of superconducting detectors. I joined forces and wrote a proposal to NASA with Andrew Lange and Jamie Bock. Andrew was just joining the Caltech faculty at the time, and it was one of the first things I did with Andrew when he started, and his post-doc at the time, Jamie Bock, who's now a professor.

We wrote a proposal to develop detector arrays for the millimeter and submillimeter, including some ideas I was working on, involving superconducting detectors. That proposal got funded, and it became clear that it was actually the idea that Jamie and Andrew were working on, the so-called spider web bolometers, was the right thing to focus on at that time in the mid-90s. Those were basically high-tech versions of Frank Low's germanium bolometer and ended up being very successful and providing the detectors that flew on Herschel in the SPIRE instrument and on the Planck Cosmic Microwave Background Satellite. The spider web bolometers were getting developed at the JPL Microdevices Lab. With Andrew and Jamie, we started working on an instrument called Bolocam for the Caltech Submillimeter Observatory using that spider web detector technology, and that ended up being a successful instrument and did good science. Sunil Golwala, now a professor, was deeply involved in Bolocam. But I was not satisfied with the state of detector technology, and there were attempts to improve the situation to make detectors that were both more sensitive but also simply larger in terms of the array sizes.

The array sizes were pretty limited. Bolocam had something like 144 detectors total, and that was a huge jump from previous instruments. In 2000, the Trustees visited Mauna Kea and I was hosting a group of them at the CSO, explaining how we had only 1 detector in 1990, 20 detectors by 1995 or so, and now 144 detectors with Bolocam. David Baltimore was listening, and he turned and said, so is that doubling about every two years?'' – to Gordon Moore! So I was always thinking of how we could move past that and come up with detector arrays that were much, much larger. There was work on a superconducting version of the kind of technology that Andrew and Jamie were using, this bolometer technology, which was called the transition-edge sensor. Basically, Frank Low's germanium thermistor got replaced by a superconducting strip. It's a very old idea that was being developed again by the mid-90s, by Caltech alum Kent Irwin (B.S. '88), who was then a grad student at Stanford and is now a professor there. Then came clever ways of expanding array sizes that were proposed by the later 90s, by Kent and his colleagues at NIST Boulder, that involved use of superconducting devices known as SQUIDs. But I was dissatisfied with all of that. It just seemed to me that wasn't the right answer long term. That's ultimately what led to the invention of these kinetic inductance detectors by 1999, just continuing to think, "Is there a way to do this that's simpler and better?" And the seed of the idea came when Rick Leduc and I were talking about this one afternoon over coffee a Peet's, on Lake and California, around June 1999.

ZIERLER: Just to give a sense of how innovative the MKID concept is, what's off-the-shelf? What are you building on from extant projects, and what do you really have to make up out of whole cloth?

ZMUIDZINAS: When we started, we weren't yet working on any similar devices. It was basically starting with equations on paper about how this idea might work and nothing except the theory to point to to support the concept. It was, "Here's an idea for how to make a detector that might solve these problems we're dealing with. Let's see if we can turn this into something real." The first thing we did was to make some simple test devices just to explore whether there was any hope of actually making detectors using this idea. We did that very quickly, in the space of about six months. We made some test devices, measured them at low temperature. We did have the necessary equipment to do that in our lab from other projects – cryostats, microwave gear, etc. These kinetic inductance detectors are small micro-resonators made using microlithography techniques and superconducting thin films. You deposit a superconducting thin film, and you make it into some kind of pattern using lithography. It's an electrical superconducting resonator with a resonance frequency in the microwave region at a gigahertz or a few gigahertz.

We were hoping to see these resonators have a high-quality factor. In other words, if you could essentially ring it, it would remain ringing for a long time. Just imagine striking a bell. You hit the bell, and the sound persists for quite a long time. That's the same idea with these resonators. If you could excite them, and if the oscillation could persist for a long time, we would be in business with this detector idea. We needed to measure if we could make these micro-resonators have what's called a high quality factor or Q. So Rick LeDuc at the Microdevices Lab made some test devices, and the very first measurements, by graduate student Tasos Vayonakis, turned out to be reasonably successful. We became convinced that this could actually work from those early measurements. There was a lot of work left to do to turn it into the ultimate dream of large detector arrays being used for astronomy. But those were some of the initial steps. Once we were able to make those initial test devices and measure them, we had the material we needed to put into proposals for funding to actually develop this idea for real.

ZIERLER: The idea of exploring the distant universe from a submillimeter perspective, were there any advances in theoretical astrophysics or cosmology that made that pursuit seem relevant or feasible at that time?

ZMUIDZINAS: Some of the papers Andrew Blain was writing when he was a graduate student in the early and mid-1990s. He was working with a quite-famous astrophysicist, Malcolm Longair, who had been interested in this topic for quite a while. I think his interest may have even been sparked by Frank Low's paper back in the late 60s, I don't know. But at the end of the day, the real issue was whether these galaxies were actually out there, how many of them were there, and if we could detect them. It was the COBE measurements that said, "Yes, there's something out there." Then, fairly shortly afterwards, around 1998, the first example of these started to be found by an instrument called SCUBA that translates to Submillimeter Common User Bolometer Array, which was a camera on the neighboring telescope to the CSO, the James Clerk Maxwell Telescope, a 15-meter submillimeter telescope on Mauna Kea. SCUBA started to find these galaxies by taking deep images of the submillimeter sky from Mauna Kea and finding a few places where there was something shining there. That really kicked off the observational exploration of this population of galaxies. The early going was quite difficult because SCUBA would find these galaxies, then the rest of the astronomical facilities including the Hubble Space Telescope, would have a really hard time seeing the galaxies that SCUBA was finding. In many cases, a galaxy that SCUBA had found to be quite bright in the submillimeter would be completely invisible to the Hubble Space Telescope, so making progress on their study turned out to be a bit of a challenge, especially in those early days.

ZIERLER: Does all of this flow directly into Z-Spec?

ZMUIDZINAS: Yes. Already by the late 90s, we were convinced, especially with the SCUBA discovery, that this field was really going to be opening up. By then, we were involved in Herschel, which was happening, and the spider web bolometer technology that Jamie and Andrew had been developing was going to be used on Herschel in a camera. It was clear that this instrument, called SPIRE, would likely find many, many examples of these submillimeter galaxies across the sky, so we were wondering how to make the next step, how to start to characterize these objects spectroscopically. That's what optical astronomers do, they find galaxies in their images, then they take a spectrograph and look for spectral lines. From the spectral lines, they can, first of all, measure the redshift, measure the distance to the galaxy, but then also start to learn something about the galaxy, depending on what spectral features are showing up and what their intensities are, and that allows you to say more about what is happening in the galaxy.

We were interested in doing the same thing at millimeter wavelengths using the CSO, but we needed an instrument that would be capable of measuring redshifts directly in the submillimeter. The problem is that if you don't know the redshift, you don't know the wavelength where the spectral lines are going to show up. That means that the instrument has to cover a very broad wavelength range so that no matter where the spectral lines land, they're going to land somewhere in your instrument, and you're going to be able to find them. You need a wide wavelength range for your spectrograph. That was what Z-Spec was built to be. There was no instrument like that at any observatory at the time, and this was the first time anyone had built an instrument like it at millimeter or submillimeter wavelengths.

ZIERLER: What does Z-Spec mean?

ZMUIDZINAS: Z is the symbol for red shift. When you say what the red shift is, you say z equals two or z equals three. Spec is spectrograph. I can't claim I came up with the name, but somehow that's the name that stuck.

ZIERLER: And this was a collaboration, really, with colleagues all over the world. This was not just a Caltech/JPL project.

ZMUIDZINAS: The seed of it was a conversation I had with Jamie Bock. We were both thinking along the same lines, that trying to do wide bandwidth spectroscopy at millimeter/submillimeter wavelengths was an interesting direction to pursue. We had been coming at it from different angles. I had been thinking about what you might be able to do using superconducting device technology, and I had been discussing ideas with Harvey Moseley at NASA Goddard, who's a quite well-known detector expert and astrophysicist. Also, my former student, Rob Schoelkopf, who by then was then starting up as an assistant professor at Yale, had been doing work on a particular kind of superconducting detector that seemed interesting at the time, which could be very sensitive, a superconducting tunnel-junction detector. John Mather was involved in these discussions. John's title is Senior Project Scientist for the James Webb Space Telescope. He won the Nobel Prize for work done with COBE. He was in the thick of this, and there were other people we were talking to. But I was thinking about how to use superconducting technology to make a spectrograph. Meanwhile, Jamie was thinking about how to take instrument designs from the visible and infrared and translate them to these longer wavelengths, to use something like a grating spectrograph. Neither was the right answer at the time, but it turned out that by blending these ideas, we could actually make an instrument work. The challenge with Jamie's approach–other groups, including Reinhard Genzel's in Germany, were thinking about similar things.

Reinhard's comment was that they couldn't figure out how to make it smaller than an old VW bus from the 1960s, which is, I suppose, how somebody from Germany would describe it. The same thing was happening with Jamie's efforts along these lines. The instruments were going to be way too large. Meanwhile, the kinds of superconducting things I was thinking about with Rob Schoelkopf and Harvey Moseley were exciting, because they could be made very compact. But it was future technology, not today's technology. If you wanted to build an instrument today, it wasn't ready for that. But what we ended up doing was to basically build a grating spectrometer, but instead of having a grating in free space like the visible and infrared instruments do, we sandwiched the grating between two metal plates, which makes it kind of a waveguide. By doing that, the instrument size could be shrunk way down. It was essentially a compromise between the two approaches. With the superconducting approaches, it was all guided-wave structures using superconducting films on a chip. You could make it really small. So instead of using guided-wave superconducting structures, we used guided structures made by machining metal.

Somewhere in between. It was the idea that was practical at the time to actually implement. The idea for the superconducting spectrometer was actually based on a microwave printed-circuit version developed by John Lovberg (B.S. '81), my Caltech classmate, who talked about it during a seminar in 1999 organized by Sandy Weinreb. Then we thought about making a machined-metal version using rectangular waveguides. Our earliest proposals described that idea. But we were also looking at what was happening in photonics, which are integrated circuits for processing light, and I gave Matt Bradford a paper to look at that used curved gratings. There was a lot of interest in such things for optical networking, the idea of sending multiple lasers down the same fiber using a technique called wavelength division multiplexing. And Matt came back with basically the design we ended up using, a curved grating sandwiched between two metal plates. In other words, we slowly zeroed in on the right idea. At that point, we started accreting collaborators. Jamie, through his work perhaps all the way back to his PhD, had good collaborators in Japan, including Hideo Matsuhara. In France, there was Lionel Duband, well-known for cryogenics, the helium-3 refrigerators, and so on that you would need to cool the instrument. Another important collaborator was Jason Glenn, who had moved to the University of Colorado but was a post-doc at Caltech in the late 90s. In fact, at Caltech he had been working on Bolocam, so we knew Jason very well and recruited him to participate in the project. Another person we recruited was Matt Bradford, who was finishing up his PhD at Cornell at the time with Gordon Stacey, and we convinced him to come to Caltech to work on this instrument. He received an experimental fellowship to do that. At the time, it was called the Millikan Fellowship, although we don't use that name anymore. But he got a prize fellowship to come to Caltech to work on that instrument. He was really one of the key people who made that project successful. Finally, my student Bret Naylor (PhD '07) wrote his thesis on Z-spec, and is now at JPL working on the commissioning of the James Webb Space Telescope.

A decade later, in 2010, we returned to the idea of a superconducting spectrometer. Tom Phillips' former student, Attila Kovacs, came into my office to talk. He had been working on superconducting receiver design and had started to think about basically a superconducting version of Z-spec. Together we came up with an idea that was even better than the superconducting spectrometers we were thinking about in the late 1990s, and we now also had the right kind of detectors to use – the superconducting kinetic inductance detectors were going great. So we started a project we ended up calling SuperSpec. We brought in a prize postdoc, Erik Shirokoff, who is now on the faculty at Chicago and continues to work on this. We recruited other collaborators, including Dan Marrone at U. Arizona – incidentally, I served as his freshman advisor at Caltech. But when I became Chief Technologist at JPL, I asked Matt Bradford to lead the project, because I knew I wouldn't have enough time. Today, there's a lot of excitement about using large arrays of these on-chip spectrometers to map the universe in 3D using a technique called line intensity mapping, and SuperSpec team members like Kirit Karkare (B.S. '11; now at U. Chicago) are now writing papers about what that might mean for cosmology.

ZIERLER: Was the siting decision already made at the beginning point? Or that can only come after Z-Spec is completed?

ZMUIDZINAS: We always had the idea in mind that we were building an instrument for the Caltech Submillimeter Observatory because that was by far the easiest place to use the instrument, and in many ways, at the time, it was the best place to use the instrument. Obviously, a bigger telescope is preferable if you can get access to a larger telescope. That's helpful if you're trying to detect distant objects that are very faint. You'd like the biggest telescope possible. But the CSO was on a good site, and we knew we could make the instrument be quite sensitive, so we thought we had good prospects to do good science using Z-Spec on the CSO. That was our main thrust.

ZIERLER: And you mentioned conversations with Jamie about this being an interesting direction to go in. To broaden out from that, what were the sciences objectives of Z-Spec? What was happening more broadly in the field that convinced you this was a good direction to go in?

ZMUIDZINAS: As I mentioned, these galaxies being discovered by SCUBA in the submillimeter were showing up as these bright objects in these images. You knew there was a galaxy there, but you didn't know the redshift. You looked at it with the Hubble Space Telescope and saw nothing. The first thing you wanted to do was obtain a redshift, find out how distant the galaxy was. But if you couldn't see it with Hubble, you wouldn't be able to get an optical or near-infrared spectrum to measure the redshift, but you could try to do that with Z-spec at millimeter wavelengths. Then, of course, if you could detect several spectral lines from the galaxy, you could start to learn a little more about what was happening in that galaxy. You could start to learn something about the star formation rate, for example, or how much molecular gas there might be in that galaxy, fuel available to form stars. The idea was to push beyond just finding these things on the sky that you couldn't really say much about, to start to learn more about those objects, to push our understanding of these submillimeter-bright galaxies further. Those were the main goals. And we knew there were going to be more such candidates coming, especially after the launch of Herschel. That's what we were really preparing for, getting a lot more candidates from Herschel.

ZIERLER: Just for a sense of scale, when you're talking about distant galaxies, how distant? How far out are we looking?

ZMUIDZINAS: These galaxies are at cosmological distances. I mentioned the term redshift, z. A nearby galaxy might have a value of z that's much less than one. It might be 0.01, which is very nearby. But the most distant galaxies known today have red shifts that are z of seven or eight, so rather large values. Those galaxies are being seen at a time when the universe is considerably less than one billion years old. The universe today is 13.8 billion years old. You're seeing galaxies that were forming, and forming stars, at a fairly early stage in the history of the universe, which is very interesting to study to try to understand the history of galaxy and star formation over cosmic time.

ZIERLER: The scale for redshift is one that's measured in time, not distance?

ZMUIDZINAS: Redshift is a useful measure for astronomers because it's dimensionless. It's not meters, it's not seconds, it's not distance or time. It's just a plain number. The redshift basically tells you how much longer in wavelength you're seeing a particular spectral line. If the object was nearby, say the object would show up at a wavelength of one millimeter. If the object is at redshift three (z=3), then the wavelength you see the spectral line is one plus z, one plus the redshift times longer (1+z). One plus three is four. Instead of showing up at one millimeter for a nearby object, it would show up at four millimeters for this distant object. These are just made up numbers, but the redshift simply tells you by what factor the wavelength of the light has expanded as a result of the expansion of the universe. It tells you, essentially, how much the universe has expanded since the light was emitted versus the time we on earth have managed to measure it. You can convert that number into a time after the Big Bang, which I mentioned. You can convert that number into a distance. But if you read a scientific paper about galaxies, it's just going to have z in it.

ZIERLER: You mentioned going to galaxies as far as when the universe was a billion years old. What about going even closer to the Big Bang? How close can we get at this point?

ZMUIDZINAS: As I mentioned, galaxies are being studied today at red shifts above seven. Many of the most distant galaxies are being studied in the submillimeter by ALMA, this big array in Chile. It has really been doing a spectacular job of performing measurements and seeing spectral lines from these galaxies at very high red shifts. It's really an extremely active area right now in astronomy. I'd have to take a specific example and convert it to years after the Big Bang, but we're talking about considerably less than one billion years, maybe 500,000 million years after the Big Bang. That's a rather short time if you think about it in terms of the time scale on which stars evolve. Our sun is several billion years old. This is happening at a time when the universe is a relatively small fraction of the age of our own sun. But you can get a lot closer to the Big Bang than that. You can study the cosmic microwave background radiation, which was formed when the universe was around 300,000 years old. And by studying the polarization of the cosmic microwave background, scientists hope one day to be able make statements about the so-called inflation that is thought to have occurred very early in the history of the universe, something like 10-30 seconds after the Big Bang. That's what Jamie Bock's series of BICEP experiments at the South Pole are trying to do.

ZIERLER: You mentioned the expanding universe. Of course, in the late 1990s, were you involved at all in the discovery leading to the understanding that not only was the universe expanding, but that it was accelerating in its expansion?

ZMUIDZINAS: The short answer is no. The acceleration was primarily a result of measurements of supernovae in distant galaxies and using supernovae as a way to measure the distance to distant galaxies. This was work that led to a Nobel Prize to Saul Perlmutter, who was my classmate at Berkeley in the early 1980s. This kind of work was happening when I was at Berkeley, the seeds of this were already happening. It was started by Rich Muller and Carl Pennypacker. So people were searching for supernovae, taking advantage of the fact that CCD cameras were becoming available in the visible, and you could set up robotic telescopes to scan the sky, wait for a supernova to go off, and use this technique to try to discover supernovae in galaxies. The availability of small computers like the IBM PC was key to all this. Then, over time, you try to find these supernovae in more and more distant galaxies, and finally, to use those measurements to map out the relationship between the distance to the galaxy, which was measured by looking at how bright the supernovae got, the larger the distance, the fainter the peak of the supernova light curve is, and comparing this distance to the redshift, which tells you this expansion factor. By combining those two measurements, you could start to learn about the expansion history of the universe and this idea that the expansion is actually accelerating, at least in the recent history of the universe. Those were measurements by the optical astronomers and particularly this branch that was doing supernova surveys. The person at Caltech who was connected to that was Richard Ellis. He was a professor here and my predecessor as COO director. He's now returned to the UK. He visits from time to time. He was here maybe a month ago. But he was involved in that kind of work. That was optical astronomy. I was doing submillimeter astronomy.

ZIERLER: Did what Saul was doing register with you at the time and how he was in a race, to some degree, with Adam Riess and Brian Schmidt at Harvard?

ZMUIDZINAS: I was watching all of this at a distance, you could say. By that point, I was interacting pretty frequently with Andrew Lange and Jamie Bock and company. Andrew joined the faculty in the mid-90s and by around 2000, he had a pretty active group studying the cosmic microwave background at millimeter wavelengths. Tony Readhead was also busy doing this at somewhat longer wavelengths. I was paying reasonably close attention to what was happening in that area. This was giving me a window into the overall field of cosmology and how it was developing. That wasn't my main focus, but I had almost a front-row seat to what was happening in the cosmic microwave background area.

ZIERLER: Did your involvement in ALMA go back to the beginning with ESO in 1997?

ZMUIDZINAS: My involvement in ALMA really has been, I'd say, indirect. It has been primarily serving on review committees and things like that over the years, interacting with the scientists and technologists who were directly working on ALMA, particularly those at the National Radio Astronomy Observatory (NRAO). My former postdoc advisor, Fred Lo, was NRAO Director at the time that ALMA was being built. And the idea for a large array of millimeter-wave telescopes like ALMA goes back a long way, Frazer Owen at NRAO wrote a memo about that way back in 1982, when I was maybe a year into grad school. But probably the biggest impact my work has had on ALMA was simply to demonstrate the superconducting receiver technology that ALMA is using. We were at least among the first, if not often the first, to demonstrate receivers working at shorter wavelengths, at the higher frequencies, and were very often leading the way in terms of achieving sensitivities that were demonstrating that the technology would be successful if used for something like ALMA. And smaller things like demonstrating various kinds of superconducting materials, kinds of superconducting tunnel-junctions. We broke a lot of ground that ALMA ended up taking advantage of later on. But we did not pursue actually directly in our laboratories building instrumentation that would go to ALMA. That was really not very appropriate for a university group to be undertaking. It was too much of an industrial scale kind of activity to really be a good fit for a university.

ZIERLER: What was the design review process aspect of this you were involved in?

ZMUIDZINAS: I was mostly involved in reviewing the plans for the instrumentation, for the receivers. I don't remember the year, but it was probably in the late 90s, I served on a review panel that reviewed what the plans were for the receivers for ALMA. There were a number of design decisions they were making at the time about what frequency ranges should be covered in different receivers and how they should be packed into the cryostat. There were a lot of details the panel was charged with reviewing, basically providing advice to the people in the trenches in the ALMA project about how to build this rather complex thing they were attempting to build.

ZIERLER: Separate topic, the NASA Origins Roadmap Project. First, is that more of a one-off project, or does it have a cyclical nature to it like the decadal survey?

ZMUIDZINAS: I'd say this was one of quite a few of various NASA committees or activities that over the years I've been involved in. NASA engages the US science community in various ways in deriving its plans for the future. That was an exercise where I'm not quite sure whether my influence on that particular committee really ended up making a substantial difference one way or another. That's just the nature of it. Sometimes, due to whatever the circumstances are, you feel like your presence on some advisory body actually matters, where in other cases, maybe it didn't matter that much. I'll point to one where I feel like it actually did matter. In 2013, I served on a NASA committee asked to describe a 30-year road map for NASA astrophysics. This was a report released in 2013 called Enduring Quests and Daring Visions. That name certainly sounds like a NASA report. In that report, I contributed material on the future possibilities in the far-infrared. That ended up resulting in a study being performed in preparation for the 2020 decadal for a major mission, roughly $4 or$5 billion, which the Astro2020 Decadal Committee considered. In fact, it's a mission they recommend pursuing in the long run, just not tomorrow, not immediately. But there's another mission they did recommend, which looks like it has a good chance of moving forward, and that's a roughly $1 or$1.5-billion far-infrared probe. There are times when you feel like you were in the right place at the right time, and something you did actually made a difference, then there are other times. And you don't know ahead of time when you get into it which one it's going to be. [Laugh]

ZIERLER: The word origins is so tantalizing. What is it meant to evoke in this context?

ZMUIDZINAS: NASA tries to choose the names of its programs carefully. Origins is a nice word because it can mean a lot of different things. We can think of our own origins as humans on planet earth. We can think about where our planet earth originated from, the origins of our planet, our star, the Milky Way, etc. Because the word is so flexible, NASA likes to use it. It can mean any of those things.

ZIERLER: I'll raise it only because you brought it up in our initial conversation, but in the early 2000s, when did you start to get sick?

ZMUIDZINAS: It really hit in 2004. I had been diagnosed with ulcerative colitis probably circa 2000. It was during the time we were living on campus at Avery House, between 1998 and 2001.

ZIERLER: Why were you at Avery House?

ZMUIDZINAS: Well, Avery House was completed in 1995 or 1996, and part of the plan, which, if I remember correctly, Gary Lorden, who was serving as the VP for Student Affairs, was involved in, and one of the things he decided would be a good idea to include were apartments for faculty in residence who would live among the students. When Avery House opened, Geoff Blake and his family went to live in one of the apartments. They did, I believe, a two-year stint. When their time was up, we decided it might be fun to do. We applied, and we were invited to move into the apartment Geoff and Karen Blake had occupied with their son, Garret. We had a lot of fun. It was, I'd say, a memorable experience. I'm glad we did it. Incidentally, as an undergrad I took Gary Lorden's course in probability, Math 144, which I really enjoyed.

ZIERLER: Did you sell your house? What did you do with your house in the interim?

ZMUIDZINAS: We had a house in Altadena, and we rented it out to a JPL couple. But then, in 1999, our second child was born, and we started to wonder if we should renovate and add a bedroom. We decided no, we weren't happy with those options, so we decided we'd sell the house and try to buy a new one that would be larger. That's what we did. We sold the house, and a few months later, we bought the house we currently live in. But the house we bought needed a lot of remodeling, and that turned into quite a long project to get it to where it is now.

ZIERLER: Perfect for you, you could stay in the apartment at Caltech.

ZMUIDZINAS: We had the idea that we would get the kitchen remodel done over the summer, then in the fall, we would move in so that the new faculty family moving into the Avery apartment could get settled in before their kids needed to start going to school. Unfortunately, our kitchen was nowhere close to being done. It wasn't done until January the following year. We had to leave Avery and move into our house, and then wash our dishes in the bathtub, cook our meals on the barbecue grill outside, etc. [Laugh] It was a challenging time, but it all worked out. We kept working on fixing up the house for many years.

ZIERLER: And things got bad for you in 2004?

ZMUIDZINAS: Yeah, the colitis seemed to be under control with a fairly moderate dose of immunosuppressant medicine. Then, for whatever reason, the medicine stopped working, and I went through a series of other prescriptions, each one progressively harsher and more difficult for the body to take. Nothing seemed to work after that point. It just seemed to spiral out of control. By the end of 2004, I had lost something like 50 pounds in the space of a month and a half or two months. The only option remaining for me was surgery, which happened shortly after Christmas that year, then I was recuperating starting in 2005, although I needed a second surgery a few months later. It was a two-step surgery, which was the way it was supposed to be. Then, the recuperation period ended up taking far longer than I had thought. It turned out to be harder. I had a number of episodes where I would land in the hospital emergency room. I had a few follow-up surgeries to try to fix the problems. So 2005 was a challenging year from that standpoint. Then, things got better bit by bit over the years.

ZIERLER: What were the big projects you had to back-burner at that point when you were not well?

ZMUIDZINAS: We had started working on these kinetic inductance detectors. With the help of those early measurements, sort of a proof-of-concept measurement, we managed to land a pretty sizable NASA grant, which allowed us to start building a team, which included Ben Mazin, who was a graduate student at the time and is now a professor at UC Santa Barbara, and others. And we were lucky to get Peter Day at JPL involved, he had done his PhD in low-temperature physics with David Goodstein. This led to the paper in Nature in 2003 that demonstrated the idea of actually detecting photons. In that paper, our photons were x-rays. That was our first attempt. But it demonstrated the idea. The next step was going to be to start adapting the idea to build a real instrument for the CSO. As a result of getting sick, I wasn't able to really push on that for a little while. That would probably be the thing I would say took the back burner as a result of my getting sick. The other projects I was involved in at the time included Herschel, SOFIA, Z-Spec, and probably a few others, including the tunnel-junction receivers for the CSO. Those projects were already up and running and had people who could continue pushing them, like Matt Bradford on Z-Spec. We had professional staff hired for SOFIA, so those projects could keep moving. And I had some really good students working on kinetic inductance detectors in the lab at the time, including Jiansong Gao, who has continued to push their development at NIST. But getting a new instrument that was going to use this new detector technology up and running was going to require a fair bit of work on my part.

ZIERLER: Given how lengthy the recuperation was, did you have to take a leave of absence? Were there graduate students in suspended animation at this time?

ZMUIDZINAS: What I managed to do was continue working largely from home during that year. I could sit at my computer, I could write, I could exchange emails, I could talk to people by phone, and occasionally meet with people in person. It was almost like COVID. [Laugh] I managed to keep working, although I'd say the intensity level during that period was nothing like either before or after. I had to slow down a little bit, and that also meant learning to delegate. There was another project I should mention that was just getting going in 2003, which was the idea to build a much larger successor telescope to the CSO. This was called the CCAT project, the Cornell Caltech Atacama Telescope. The idea was to build a large submillimeter telescope, maybe 25-meters in diameter, quite a bit larger than the ten-meter CSO, and to put it on an excellent site in Chile. There were a couple of options for a mountaintop site that were being considered. That was just getting going in 2003. We had some preliminary meetings with people from Cornell. Tom Tombrello, who was division chair at the time, made available a fair bit of funding to start studying and shaping this idea. There were going to be study funds available at Cornell and Caltech, and the idea was to put together the whole project concept. That was one thing during that year I was sick in late 2004 through the first half of 2005 I wasn't able to participate in as much as I would've liked. We had hired a person at Caltech to help with that, Simon Radford, and he ended up doing a fair bit of work at the time. But my involvement took a back seat during that period.

ZIERLER: You'll have to explain to me the timing. When you start with JPL, was that already agreed to before you got sick? Or these were in discussions as you were coming out of recovery?

ZMUIDZINAS: I first met Tom Prince, now a retired professor, when I was a senior at Caltech in 1981 and he was a post-doc in Ed Stone and Robbie Vogt's group. I was just leaving that group to go to Berkeley, and I remember briefly meeting Tom before leaving. Many years later, Tom Prince was now serving as Chief Scientist at JPL, and Tom was thinking it would be a good idea to start a program where Caltech faculty would hold a joint appointment at JPL and would actually commit to spending some time physically at JPL. I was the guinea pig for that program. [Laugh]

ZIERLER: Did you have any interaction with Charles Elachi before this?

ZMUIDZINAS: Yes. In fact, when we were starting to really flesh out our ideas about superconducting detectors–and it wasn't just this kinetic inductor idea we talked about. I was involved in the work that Andrew and Jamie were doing in cosmic microwave background detectors, and I mentioned the spider web bolometer technology they were using. Basically, that was a high-tech version of Frank Low's germanium bolometer from the early 1960s. So by the late 1990s, they knew that they needed to move on to a more advanced technology and knew that the future for them involved superconducting detectors. I was meeting with them and discussing ideas quite often, and I helped shape their concept for what their superconducting detectors for microwave background measurements were going to look like. I contributed some technical ideas for that, then they started pursuing that program. By the early 2000s, we had a pretty big vision about what we, Caltech and JPL, ought to be doing in superconducting detectors. We started to share that vision with people, especially people at JPL. We invited Charles–and this was probably before he formally became director–and a number of senior JPL managers to come to campus so that we could describe this vision about what we together could be doing in superconducting detectors.

I had already known and interacted with Charles by this point. I should also mention that my wife, by then, was good friends with Valerie Elachi, Charles's wife. In fact, my wife had started working in human resources on campus by the mid-90s, and one day, maybe '97 or '98, Bruce Murray, the former JPL director, came to my wife's office and asked her to come work for him as his assistant. She said no, then a few months later, he came by and asked her again. [Laugh] Second time, she said yes. She ended up working for Bruce Murray on campus as his office assistant, doing everything and anything, helping prepare proposals, correspondence, grant management, things like that. But when she became pregnant with our second child, she stepped away from that, and Valerie Elachi ended up taking over as Bruce's assistant. My wife made the connection between Bruce and Valerie. We had known Charles as a result of that, the social connections, events at the Athenaeum and things like that, in addition to the professional connection.

ZIERLER: The title, senior research scientist, sounds almost broad enough that you can make it what you want. Or is that a pretty defined role in actuality?

ZMUIDZINAS: The Senior Research Scientist title at JPL is intended to be a recognition of, you could say, the top echelon of scientists at JPL. These are people whose scientific achievements and contributions are judged to be comparable to tenured faculty at research universities. The review process at JPL specifically asks that question, basically, "Is this person comparable to a tenured faculty member?" Tom Prince's idea was that if we were going to have faculty joint appointments, where we take Caltech faculty and ask them to spend time at JPL, that those faculty are in fact tenured faculty members at a research institution, and therefore, they should also be awarded this designation of senior research scientist at JPL. It was a way of communicating to the JPL staff of how people should think of these joint appointments in terms of the broader landscape at JPL, how they fit into the JPL system.

ZIERLER: The obvious question here is, how do you make sure you don't accidentally take on a full-time second job?

ZMUIDZINAS: That's exactly what happened. Paul Dimotakis, who by then was serving as Chief Technologist at JPL, was dealing with the issue of the JPL Microdevices Laboratory. There were questions about what JPL should do in that area, how firm JPL's commitment should be to the Microdevices Laboratory, whether it was something that was an institutional priority for JPL to be supporting and improving or a business JPL should be getting out of. Paul, as chief technologist, was in the center of this high-level discussion at JPL. He asked me if I could do a study, essentially, and produce a report about what was actually happening at the Microdevices Laboratory, how it fit in, why it might be important, etc. Being a good citizen, I did what he asked me to do, and I essentially interviewed all the groups, group leaders, and people who worked there, assembled all their slides, compiled all this material, and gave it to Paul. The next thing I knew, Paul was asking me to serve as the JPL Microdevices Lab director.

ZIERLER: To the extent that the job title is amorphous enough, were you able to integrate submillimeter astronomy introduces into what was happening at JPL? Were you able to fuse those worlds at all?

ZMUIDZINAS: Yes. Obviously, Herschel was a submillimeter far-infrared project that JPL was deeply involved in. In those years, there was still activity at JPL, although with the Herschel launch in 2009, the second half of the 2000s, a lot of the hardware deliveries, etc., had already been made to the project. JPL, in some sense, was preparing for the science that was to come with Herschel as opposed to doing instrument and technology development for Herschel, so things had morphed a little bit by then. But there was a lot of interest in what would come after Herschel. In the 2000 decadal report, there was a recommendation for a mission that was called SAFIR, which stood for Single-Aperture Far-InfraRed Telescope. It was a recommendation that wasn't at the top of the list in the decadal, which meant it wasn't actually going to happen that decade, but it was interesting enough that NASA and JPL were looking into what they could do, so there were SAFIR-related activities happening at JPL that I got involved in at a moderate level. But the main thing, I would say, in those years was CCAT. We were working with Cornell to try to make this into a real project. There were engineering activities for CCAT happening at JPL, and I was the person who was trying to glue this all together. At the same time, in my role as JPL Microdevices Lab Director, we were continuing to develop the superconducting detectors we needed for CCAT, so I continued to be deeply involved in that work, which had a significant footprint in the Microdevices Lab. But at the same time, as Director I was being asked to take a bigger-picture view of the Microdevices Lab and not just think about superconducting devices and detectors, but everything happening in that lab. It was a busy time.

ZIERLER: Did you stay involved continuously through your next position as chief technologist, or was there a break in between?

ZMUIDZINAS: Basically, my job as Microdevices Lab director, I think I fairly quickly realized, was a job of defining and communicating the value of the Microdevices Laboratory to the rest of JPL and to NASA. We took a number of steps to try to raise the profile of the Microdevices Lab. One example is that we started issuing an annual report, and it was an annual report where we actually spent some effort to try to produce a nice product, something people would enjoy looking at. The idea was to put this into the hands of especially senior management at JPL so that they could learn more about what was happening at the Microdevices Lab. We completely revamped the lobby of the Microdevices Lab with nice graphics on the walls, and in the basement, where the clean room actually was, we revamped all the displays. The Microdevices Lab became a favorite tour stop. Whenever important people were visiting JPL, senior managers would bring them through because it was a nice place to visit again. It was things like that, opportunities for improving communication, that we were looking for. But also, we invited a group of senior people to come review what was happening at the Lab and to give us advice. People at other national laboratories like Sandia, or people at DARPA, or prominent professors at other universities, and we would use the reports they provided as a way to communicate to JPL why what we were doing was important and how JPL could help. Those are the kinds of things we were doing. As a result of those kinds of activities, I suspect that more people at JPL started to know who I was, and I suspect that had something to do with why I got asked to serve as chief technologist.

ZIERLER: At the Microdevices Laboratory, how strongly oriented is it towards specific missions?

ZMUIDZINAS: The ultimate goal is to have an impact on missions. The basic idea of the Microdevices Lab is that we have these fantastic tools that are the result of billions upon billions of dollars of investment by the semiconductor industry. Every year, they're making large investments in improving the state-of-the-art in microtechnology and all the tools used therein. And we could take advantage of that massive investment and bring those tools into the Microdevices Lab, then use them for our own purposes, for applications that were relevant for JPL and NASA missions. But often, that means you're starting from zero, from an idea for a technology, and you have to prove out that idea, make it real, and get it to a level where NASA and a hard-nosed JPL project manager are willing to bet a mission which may cost a billion dollars or more on this technology that's coming out of this lab. It's a really tall order. But that's the goal, and it's an incredibly ambitious goal, but nonetheless, it's a goal the Microdevices Lab has delivered on numerous times over the years.

ZIERLER: What were the expectations in terms of all your service and advisory work back on campus? In other words, the more responsible you have at JPL, is there a decreased expectation of what you can do on campus?

ZMUIDZINAS: Certainly, the time I was serving as chief technologist, I was no longer teaching. That had to go. In fact, the chief technologist position, I found, to be nearly all-encompassing. I had perhaps one day a week I could devote to campus activities, keeping in touch with my research group, and so on. There definitely is a price that you pay in terms of your ability to keep up your campus activity when you take on a role like that. Of course, one of the reasons to do it is, it's a learning experience. In many ways, I really enjoyed the opportunity that JPL has provided me in completely changing up what I've been doing in my career without physically having to move to a different institution or city. It's been a way to continue growing professionally in different directions, and yet be at the same home institution. It's really, I think, a remarkable opportunity that I've enjoyed.

ZIERLER: Does the chief technologist report directly to the director?

ZMUIDZINAS: Yes.

ZIERLER: What were the kinds of things you'd talk about in a one-to-one with Charles Elachi? What would rise to that level?

ZMUIDZINAS: Charles would start those one-to-one meetings with a simple question: what have you got for me?'' That was an invitation to bring forward whatever issues were most pressing or relevant. Often it was about money, funding for research projects or a major piece of equipment, but also personnel, organizational issues, interactions with NASA Headquarters, stuff like that. At JPL, there's also an executive council consisting of the people who report directly to the director, in my case, Elachi. There are meetings of the executive council that would happen either once or twice a week. There would be any number of additional meetings on various topics that I would participate in as a result of being a member of the executive council. And there was an annual retreat where we would spend several days talking about the big-picture issues for JPL. You really were part of the senior management team of JPL by being a member of the executive council. That meant I was being exposed to not just technology issues, but everything across the Lab, from human resources, to finances, to building upgrades. It ran the gamut. Everything happening at the Lab was getting discussed at the executive council. The kinds of things I needed to pay attention to were obviously technology-related. JPL has a fairly sizable amount of money called the Research and Technology Development Program, R&TD, which was running about $50 million a year when I was there. Essentially, my role was to ride herd on the technology-related activities that were being supported under that program. That meant running proposal reviews. We would put out calls for proposals to the JPL community, we would receive proposals, we'd have to evaluate them and decide which should be funded and how much. That was a significant part of the job, actually making decisions and recommendations on how to use these important resources. But then, also, at that time, there was a renewed emphasis on technology at NASA headquarters. Bobby Braun had taken on the position of NASA Chief Technologist, reporting to the NASA Administrator, and that position hadn't existed for a while. He came and started this new technology office at NASA. We had a lot of interactions with NASA headquarters and the people in this new technology office that Bobby was starting up, a lot of discussions about what kinds of technology programs at NASA and JPL should be funded. A lot of travel related to that, a lot of meetings at various NASA centers related to that. There were additional funding channels coming to JPL from that office, some of which my office was responsible for managing. So my domain was basically a rather broad portfolio of technologies, whether for planetary missions, earth science, astrophysics, or simply spacecraft technologies, things that would make our spacecraft better, and then this was tied up in all of the issues about which NASA missions were actually going to happen or not happen. It was fascinating. It was a lot of fun. ZIERLER: What were the missions as chief technologist that you were most closely involved in? ZMUIDZINAS: Obviously, there's a rather large gap in terms of time between when technologies get developed and when they finally get used on missions. In most cases, the kinds of technologies that we were investing in and pursuing, it was going to be years before they ended up making it on a NASA mission. I wasn't involved in mission project work directly very often because by that point, the technology was done. It was a matter of implementing it for the mission. I was involved in the earlier phases. If I somehow managed to get involved in a mission project, it was usually bad news for that project. [Laugh] Because technology not working presumably would be the only reason my office would get involved. I can tell you some of the things we did, and this is still playing out at JPL to this day. We decided that we really needed to try to define a few thrusts where JPL really ought to be focusing in. Some were already pretty clear. In astrophysics, a fundamental area of technology is detectors. If you don't have good detectors, it's very difficult to see distant objects. You need good detectors. But there's more to it. There are telescope technologies and so on. But we decided to take a really broad look at technologies across all of JPL and try to identify a few areas where JPL needed to be thinking and investing long term. We had these technology retreats my office organized. We would invite an interesting cross-section of leading technologists across the lab, people from NASA headquarters, speakers from outside of NASA and JPL, those who were involved in interesting aspects of technology. One of the most memorable of those was Lars Blackmore, who was the principal rocket landing engineer for SpaceX, and is now the principal Mars landing engineer there. He gave this fascinating talk. This was the early days when they were trying to land their boosters. You've probably seen videos, how they send their rockets off, then they turn around and land. He showed us video after video of failed landings, these things blowing up, then finally successful landings. [Laugh] He was in the thick of it, making it actually work. He was a former JPL-er who had gone onto SpaceX to lead that activity. Through events like this, we started gathering input from key people across the lab, producing reports and so on that honed our thinking about what technologies areas we ought to be pursuing. One of them that came to the fore was autonomy. This was ten years ago. By now, people are getting tired of the buzzword artificial intelligence because it's been used so often. But this was when this recent resurgence of artificial intelligence was really nascent. It wasn't quite a thing yet. Yet, talking to some of my colleagues at other universities, I was hearing about what was going to be coming. It was already clear that industry was making big moves, at companies like Facebook and Google. Self-driving cars were starting to be discussed. It was clear that JPL really should be taking a very hard look at this area and understanding how we could apply some of the developments to spacecraft and JPL missions. And it's easy to understand why you might want to think about this. When JPL sends a rover to Mars, simply to get radio signals there and back can take an appreciable fraction of an hour, 15 minutes one way or something like that. But if you go deeper in the solar system, to Jupiter and so on, the light or radio signal travel time can be hours. If the spacecraft is always depending on a human to make decisions and take action, that really bogs things down. You want your spacecraft to be able to make decisions and take action autonomously in many cases. Often, it's the only way to achieve your objective. It was pretty obvious that both on the technical side, there were developments coming that could be taken advantage of, but also, it was a longstanding need for JPL to have such capabilities. That was an area we started to try to advance at JPL. You have to take a long-term perspective. JPL is making important investments in this area today. It's advanced since I left, and I'm glad to see that. I think we're far from seeing the end of the story. It will be many years before it's all played out. ZIERLER: Given the gap, as you mentioned, between when technology is developed and when it's implemented, today, circa 2022, are we seeing any technology that came from when you were leading the effort at JPL? ZMUIDZINAS: I can talk personally about the kinetic inductance detectors. They are the leading candidate to be used in this far-infrared probe mission, which if it actually goes according to schedule, if that mission is selected and flies, could go as early as the early 2030s. That would be a true JPL technology success story from initial invention all the way to flight at JPL. That would be terrific. But there are other technologies that are being demonstrated. I'd say that in some cases, my office played a role. To a larger or smaller degree, JPL has had a longstanding interest in using optical communications for deep space, sending data back from JPL missions in deep space using optical communications instead of radio. Research efforts at JPL have been supported through this R&TD program over the years, but you need to make that last jump, where the technology has reached a level of credibility where it's included on a mission and is used for the purpose you've developed it for. This was an example where it happened, and I remember the meeting where it happened. There had been any number of discussions at the executive council level about what we can do to advance technologies and to get things so they finally reach flight. Charles Elachi had convened an executive council meeting. If I remember correctly, we were at the Hall of Associates in the Athenaeum, and he went around the table and had the directors responsible for a number of the major missions. He pointed to them and said, "You are going to include this technology on mission X." It was by fiat from the director. That's how a number of technologies got their chance to move forward. One of them was the Deep Space Optical Communication experiment I've been talking about, which is going to be flying on Psyche, a spacecraft to study a metallic asteroid. Charles said, "You're going to include that on your mission." They made the arrangements, they talked to NASA. At the end of the day, that experiment is flying on Psyche, which is going to be launched in August, and the 200-Inch Telescope at Palomar has a role in that. It's going to be the ground station, the place where the optical data are received from the spacecraft. The receiver at Palomar is going to use superconducting detectors produced at the Microdevices Lab, a very special kind of detector known as superconducting nanowire single-photon detectors, SNSPDs. That's another example of technology, which was conceived before the time I was chief technologist, but I think we can claim to have helped nudge it along at least a little bit towards finally getting to space. I have to think of other examples, but it's a long road. From conception of kinetic inductance detectors to flight, if we're lucky, it'll be 30 years, which is relatively short. ZIERLER: If you were there that day, what was it like when Curiosity landed on Mars? ZMUIDZINAS: [Laugh] This was August of 2012. I was about a year and a half into my tenure as chief technologist. It was obviously a big event for JPL. There were venues at JPL, venues on campus with different groups of people attending. Charles had given assignments to basically every single member of the executive council, what their job was going to be on landing day. The job I was assigned was to be on the stage of Beckman Auditorium, which was going to be filled with the friends and families of the people who actually worked on the Rover project. It was the friends and families of the Curiosity Rover project. These were important people, like Trisha Stelzner, wife of Adam Stelzner, one of the key Mars landing engineers at JPL. And Beckman Auditorium is a big place. Man, was I nervous. [Laugh] We had done a lot of preparation before landing. There were a couple other JPL-ers. Dave Beatty and Gregg Vane come to mind. I wasn't alone, some experienced JPL people were there to help. But we had gotten some amount of training as to what to expect that evening. We'd been given these handouts, and the handouts described the sequence of events. The way that it went was that initially, there was going to be an entry into the atmosphere. There's a heat shield that was going to be slowing down the entry vehicle, then at some point, the parachute was going to pop, etc. And eventually you got to the sky crane, which seemed crazy. But as you went down the sequence of events, especially when you got to the point of landing and afterwards, there were branch points where A or B could happen depending on the details and depending on whether it went well or not. The problem was, as you went down, these branch points kept multiplying. I knew I could make it past maybe the first or second branch, but by the time we got three or four branches deep, I was going to be hopelessly lost in the myriad possibilities of ways things could go wrong, things that could happen or not happen. I knew I would never be able to keep up in real time on the stage of Beckman Auditorium and give a coherent story to this audience of 1,000 people about what was actually happening. [Laugh] I knew if we got there, I was totally sunk. Luckily, it just went perfectly. All the things that could've gone wrong didn't go wrong. The Mars Odyssey, which is an orbiter, had a chance to relay data back from the rover on the surface back to the earth, but that required Mars Odyssey performing a maneuver to point its antenna back to earth. In the days leading up to the landing, Mars Odyssey was showing signs of age. It was failing to perform these maneuvers properly. It was not at all clear whether it was going to be able to fulfill its role and send especially the first landing images back to earth. There were all kinds of uncertainties like that. But minutes after landing, on the screen of Beckman Auditorium, we started to see these images. What a relief, and what a wonderful feeling. It couldn't have gone better. It was an amazing evening, I have to say. [Laugh] ZIERLER: Was Jean-Lou Chameau on hand for all of this? ZMUIDZINAS: Jean-Lou was in the control room, where when you see the successful landing, everybody jumps up and down, hugs each other. Those are the key project people monitoring the landing in real time, staring at their computer screens. You've got the NASA administrator, the Caltech president, Charles Elachi in person with those people who are the real people monitoring the landing. That's where Jean-Lou would've been. All you have to do is go back and look at those videos, and you'll spot him. ZIERLER: After Curiosity, were you involved in the discussions for the next generation of Martian exploration? ZMUIDZINAS: When I became JPL Chief Technologist in 2011, JPL was looking at a fairly substantial decline in the amount of funding coming in. The spending on Curiosity Rover had peaked and was declining. JPL's funding from NASA was on a downward trajectory, and JPL had to go through layoffs in that period, hundreds of people, as a result of the declining budget. This was obviously on the mind of the director. He needed to find a way to reverse that and especially to find the next thing to do on Mars. He was very skillful in taking advantage of the successful landing of Curiosity to convince NASA and Congress that the right thing to do was to follow up with another rover, which we now have on Mars, Perseverance. There were a lot of discussions about instrumentation, science, and so on, and especially whether this could be the first step towards a Mars sample return, the idea of taking samples from Mars and actually returning them to earth for study in laboratories on earth. Another thing that was happening at that time, and especially after the Perseverance Rover project had gotten underway, was inclusion of this helicopter now called Ingenuity. That was something else Charles really was very much arguing in favor for and trying to convince NASA to do. In fact, there was a fair bit of funding from the R&TD program being used to support the early development of that concept. Without Charles' support, I'm pretty sure that the Ingenuity helicopter would not have happened. ZIERLER: To use the political expression, I assume that the chief technologist serves at the pleasure of the director, so when Charles Elachi decided he would step down, this would mean you would as well? ZMUIDZINAS: My initial appointment was for three years, then it was renewed for another two years, and Elachi was continuing as director. But by the time five years were up, I was ready, and Charles was retiring. It was really at that point only a question of what the detailed timing would be of both Charles's retirement and my leaving the position. I felt after five years that it was time for me to return to campus, that I had learned what I was going to learn in that role. It was a good time for me to step aside and let someone else take over. ZIERLER: Was it in the cards already by the time you stepped down that you would eventually take over Caltech Optical Observatories? ZMUIDZINAS: No, that came about a year and a half later, and was not on my radar at all. Mike Watkins was selected as the next director of JPL, and I ended up serving a few months into Mike's term, simply to give him time to figure out what to do about his executive council positions, which ultimately meant him selecting my associate chief technologist, Fred Hadaegh, to succeed me as chief technologist. I ended up serving a couple months just to give Mike the time to sort things out and make that decision, and I was happy to see Fred get selected for that role. By then, it was about November 2016, and Charles had retired June or July of 2016. But I was ready to return to campus. To be honest, I wasn't quite sure what I was going to do in terms of research and returning to campus. Caltech's involvement in CCAT ended in about 2014. We had managed to get the top ranking in the 2010 decadal survey, but unfortunately, the National Science Foundation didn't have the$30 million we needed from them plus the operating funds we'd need from them, which perhaps was even a larger problem for the NSF long term.

We didn't have enough funding between Caltech and Cornell alone to do the project. At that point, Caltech exited the project, which was, I'd say, a big blow to me because I had spent a lot of time both developing that concept and getting it to be real, bringing Steve Padin on board. At Chicago with John Carlstrom, Steve played a key role in making the South Pole Telescope successful, the ten-meter in Antarctica, and we hired him back at Caltech to basically be the project engineer for CCAT. He was the person who really brought technical reality to the project. We had gotten really close to making this large new submillimeter observatory happen, but at the end of the day, there just wasn't the money at the NSF. That was a big blow, and I wasn't sure what was going to happen afterwards because already in 2009, Caltech announced we were going to be shutting down the Caltech Submillimeter Observatory. That was a move essentially to pave the way for TMT to go on Mauna Kea, to show that we could not only build telescopes but remove them as well. So the CSO's days were numbered. After that announcement, there was little interest among funding agencies such as NSF to provide funding for new instruments for the CSO if the observatory was going to be shutting down.

ZIERLER: What did it mean for submillimeter astronomy in general to lose CSO?

ZMUIDZINAS: One of the reasons the NSF didn't have money was that it was trying to figure out how to pay the operations costs of ALMA. NSF had managed to raise the funding for the construction of ALMA, at least its share, through a mechanism known as MREFC, Major Research Equipment and Facilities Construction. It's a line item in the NSF budget that Congress approves, a funding channel for the NSF. That was the channel that paid for the NSF share of ALMA's construction. But that channel stops after the construction is finished. Meanwhile, funds are needed to operate. Those have to come from within the astronomy division at NSF. That meant that the NSF was scouring its budgets in astronomy to figure out how to raise $50 million a year to pay for ALMA operations. That's fundamentally, I think, the reason why the NSF was unable to do anything about this top recommendation in the 2010 decadal to build CCAT. What was happening in submillimeter astronomy was that the pioneering facilities were scrambling, like CSO, like our neighbor the JCMT on Mauna Kea, and also Owens Valley, which by that point was running CARMA, a combined array of telescopes from the Owens Valley interferometer and from the Berkeley-Illinois-Maryland interferometer located on a high mountain site next to the Owens Valley floor. All of these pioneer projects were getting displaced by this mammoth project called ALMA that was really changing the landscape in submillimeter astronomy. Nonetheless, we needed an observatory like the CSO or CCAT in order to be able to continue developing technology and instrumentation for submillimeter astronomy. Without having that, it's been a real challenge. ZIERLER: What is the status of CCAT today? ZMUIDZINAS: There was a donor at Cornell by the name of Fred Young who donated$25 million to Cornell to pursue that project. Cornell regrouped and is now building a much smaller telescope, a six-meter telescope, on that high mountain site in Chile, Cerro Chajnantor. It's a very different project. The science goals are far more modest. But nonetheless, it's a vehicle that can be used to develop and demonstrate advanced instrumentation. A lot of the instruments they're planning to use on this much smaller telescope, now called the Fred Young Submillimeter Telescope, or FYST, are going to use our invention, the kinetic inductance detectors.

ZIERLER: Is the idea that this is the best you can hope for or settle for? Or is there some hope that CCAT will be revived in the future?

ZMUIDZINAS: There have been various activities in that direction. In fact, there were a number of concepts submitted to the Astro2020 Decadal Survey, concepts for large millimeter/submillimeter telescopes. But for the Astro2020 survey, none of them had been developed to the level that CCAT had been developed for the 2010 survey. Millions of dollars were invested by the time the 2010 decadal survey saw CCAT, whereas none of the submissions for the Astro2020 Decadal Survey had anything even close to that level of investment. The Astro2020 survey, as far as I can tell, basically ignored them because without advancing a project to that kind of level, it's hard for the Astro2020 committee to make heads or tails of how real or imaginary it is. You really need to do a lot more work. That's what's needed. One of the concepts that's been on the back burner is a concept that's been pushed in Europe called AtLAST, Atacama Large Aperture Submillimeter Telescope perhaps is what it means. One of the ringleaders of that effort is Tony Mroczkowski, an Einstein Fellow post-doc in my group in the late CCAT era, 2012, 2014 or so (2011-13), overlapping with my tenure as chief technologist at JPL to some degree. Tony now works at ESO, the European Southern Observatory. He's been one of the ringleaders in the effort to study a large submillimeter telescope.

They recently have obtained a several-million-dollar grant from the European Union, some funding program in the EU, to perform a more detailed study. It looks like they're on a path that could lead to something real. When Richard Ellis was visiting, my predecessor before Shri Kulkarni as COO director, he mentioned that this large submillimeter telescope is one of the more serious contenders for what the European Southern Observatory might do after they're finished constructing the ELT, the Extremely Large Telescope, a nearly 40-meter optical-infrared telescope. It's my firm belief that a project like AtLAST will be done sooner or later, that the science is so compelling, it's something that needs to be done. By now, the instrument and detector technology have advanced to the point where it's really become quite obvious that the kind of instrumentation we were envisioning for CCAT, which I think at the time, people were maybe not certain could be achieved, can and will be. But it may be another ten years before it (AtLAST) really gets off the ground.

ZIERLER: Is there momentum that needs to be maintained by people like you so that it does get off the ground?

ZMUIDZINAS: I think it's not people like me anymore because by 2030, I'll be 70 years old, and I don't think any major project should rely on a person like me to push them forward into the next decade. [Laugh] It's really, I'd say, people like Tony Mroczkowski and others who need to find a way to keep moving forward throughout this time. One of the things that's been happening at Caltech is that Sunil Golwala, another professor, has been pushing to move the CSO telescope to Chile, a project called the Leighton Chajnantor Telescope, Chajnantor describing the region in Chile, and Leighton for Bob Leighton, the genius behind these ten-meter dishes. It's a collaborative project with China and Chile. It looks like there's a real shot that that could actually happen now, so I'm optimistic that move can be made. If the CSO moving to Chile results in a platform where instruments can be tested and developed, that will be a significant step forward.

ZIERLER: I'm curious, in directing COO, what vantage point does that give you in terms of understanding Palomar and Keck and how they fit in overall at Caltech?

ZMUIDZINAS: Certainly, much better than I had before. [Laugh] It's been a wonderful learning experience. I'm a fish out of water in that I'm not an optical-infrared astronomer, and I'm really principally not an observational astronomer. I'm a nuts-and-bolts instrument and technology person who likes to dabble in astronomy with some of the things I work on. But there are many of the same issues you have to deal with. The optical observatories live and die by their instrumentation. It can't remain static. It has to keep improving because the rest of the world keeps improving. To remain relevant and remain at the forefront, you need a continual refresh and improvement to the instrumentation. Those are the things I've been focusing on in my role as director. We have a new spectrograph that's under construction for the 200-Inch Telescope at Palomar called the NGPS, not a very imaginative name, Next-Generation Palomar Spectrograph, to replace a 40-plus-year-old instrument. Then, on Keck, we have a number of new instruments coming soon, but then also this recent \$71-million gift to really push hard on new instrumentation. Other than that, I've been really enjoying meeting the people, the Palomar staff, the Keck staff, getting to know what my colleagues at Caltech do with their time on Palomar and Keck. On the Caltech time-allocation committee that I participate in, I get to read their proposals and learn about what they're doing. It's been a lot of fun.

ZIERLER: How closely involved are you with questions about renewing the master lease for Keck in the 2030s?

ZMUIDZINAS: That's obviously a big issue, and we devoted a substantial portion of a recent meeting of the CARA board discussing that. CARA is the California Association for Research and Astronomy. The CARA board is the body that oversees Keck Observatory. The issues of the master lease renewal are of special importance to the CARA board. I also see this issue come up because of my service on the TIO board for the TMT. It's obviously very relevant there as well. It's quite interesting, and I'd say it's pretty unclear as to what actually will be happening in Hawaii. The University of Hawaii is the current leaseholder, and they're taking steps to renew their lease, but there's also dissatisfaction with the University of Hawaii as the leaseholder, and there's the opinion that's reasonably widespread in Hawaii that some other organization should take over that responsibility. Exactly what organization would do that is unclear. There was a working group that was organized by Scott Saiki, the Speaker of the House in Hawaii, to make recommendations on how the governance of Mauna Kea should be handled. They made a recommendation, which was then basically adopted as legislation that has passed the House in Hawaii and is now under consideration in the Senate, which would change the way Mauna Kea's managed and would not have the University of Hawaii involved. All of these issues are very much in flux. It's very much a hot topic right now in Hawaii.

ZIERLER: I'm thinking specifically about adaptive optics, but more generally, have there been technologies that you were exposed to or involved with at JPL that you can transfer to upgrades at Palomar and Keck?

ZMUIDZINAS: I'll mention the kinetic inductance detectors again. I mentioned Ben Mazin, who's now a professor at UC Santa Barbara. He was one of the first students we had working on those detectors back in the very beginning circa 2000. He's developed a version of these detectors for optical astronomy. And they keep getting better and better. They have very interesting advantages compared to standard detectors such as CCDs. They can detect single photons, they can tell you the energy of the photon, they can give you extremely good timing of the photon arrivals, and so on. He's put an instrument using these detectors on the 200-Inch at Palomar, and he now has an instrument on the eight-meter Subaru Telescope on Mauna Kea, the big optical telescope. I would be very interested to see an instrument using those detectors deployed on Keck ultimately. But I think we still have a fair bit of work to do to understand the best application for those detectors on Keck. There have been a number of suggestions that Ben and his group have made that I think haven't quite yet resonated with the rest of the Keck astronomers. But I'm sure that there is going to be a real killer idea that'll come sooner or later that's going to be magic. I haven't been able to come up with it, but I'm sure someone will.

But other than that, in terms of technologies, there's a lot of overlap in JPL technology interests and Palomar- and Keck-relevant technologies in the area of exoplanets. A good example is Dimitri Mawet, a professor at Caltech, who's been pushing using Keck especially for the imaging of exoplanets around other stars. The technical challenge is enormous. You've got an extremely bright star and an extremely faint planet next to it that you're trying to see, and you have to block the light from the star. A number of the technologies that Dimitri uses were actually developed while he was at JPL. He was working with Gene Serabyn on at least some of those ideas, demonstrating them at Palomar, and Gene I've known well since he was a graduate student at Berkeley. He had a major involvement in the CSO in the 1990s before he moved to JPL. When I was chief technologist, we were supporting some of these exoplanet-imaging coronagraph technologies, technologies you need for suppressing starlight to be able to image exoplanets. We've supported a number of developments in those areas. I think that's a good example of where JPL technology and science interests line up very nicely with those of Caltech and Keck especially. And there are other examples in that area. Andrew Howard is in the process of building a new instrument for Keck called Keck Planet Finder to study the motions of stars by looking at their spectra to try to detect planets around them.

It's a tried-and-true technique, and this is going to be the latest, greatest instrument for doing that. There's interest in doing the same sort of thing at infrared wavelengths, longer wavelengths. There's a JPL instrument being used at the 200-Inch at Palomar called PARVI, Palomar Radial Velocity Instrument, which is a sister instrument to one Dimitri's developing for Keck called HISPEC to try to use the same kind of technique, but in the infrared. There are a lot of technologies that both JPL and Caltech are interested in. One of the technologies is called the laser frequency comb, and the idea is that in order to detect these very subtle motions of the stars, you need an extremely stable instrument. One way to get a stable instrument is to calibrate it often using a calibration that's extremely precise. The idea here is to use a calibration that's extremely stable, spectral lines derived from a laser you use to calibrate the spectrograph that you're using to make the stellar velocity measurements. This is something else I helped to support. Chas Beichman, who's involved in all of this, came to pay me a visit at my office at JPL. We helped provide some funding to get going in that area, and that's really blossomed. Some of the key people include Stephanie Leifer (PhD '95) and Kerry Vahala, a professor in applied physics and a fellow Caltech undergrad. The laser frequency comb is going to be deployed on Keck fairly soon.

ZIERLER: I wonder in what ways working with the Palomar Observatory gives you a sense and appreciation for the depth of history of astronomy at Caltech going all the way back to Hale.

ZMUIDZINAS: It's truly amazing. I'd say that the times where I really felt the deepest appreciation for that have come in a series of two meetings so far. The first was held at Mount Wilson at the 100-Inch, and the second was at Palomar, which we hosted. Sam Hale, who is the grandson of George Ellery Hale, is quite involved in the stewardship of the 100-Inch Telescope on Mount Wilson. That telescope is no longer used for research, but they still have visitors coming, they use it for events, for educational opportunities, etc. They're looking for opportunities to expand their ability to both maintain the Observatory and also their footprint in reaching the outside community. There are other observatories that have the same interest, Lick, Palomar, Yerkes. Of course, that's another Hale observatory. We had a meeting, which was really instigated by the Mount Wilson people, but it included representatives from those observatories, and Lowell, Griffith, and a few others.

From Lick it was Sandy Faber, who's a famous astronomer at UC Santa Cruz. We had a representative from the Vatican Observatory, obviously myself and my Deputy Director Andy Boden from Palomar, the Mount Wilson people were there, and so on. This started the idea of having this Alliance of Historical Observatories (AHO) which was barely starting to gain traction before COVID hit. We now at least have a nice web site. But there's a seed of an idea there about how these historical observatories might be able to join forces and help support each other in their efforts to reach the outside community. But especially to communicate the importance of these observatories as historical sites. Sandy Faber is just extremely eloquent on this. The way she describes the discoveries made at the 100-Inch, made at Lick, made at Palomar, with humanity for the first time starting to understand the vastness of the cosmos, the enormity of the universe, the expansion of the universe with Hubble and Humason at Mount Wilson, these jaw-dropping discoveries that have been made for all of humanity. And yet, these sites, like Mount Wilson, are at such risk of disappearing. We saw the fires, which really pose a huge danger to Mount Wilson. It wasn't very long ago when the Bobcat fire came quite close to Mount Wilson (2020). Of course, there was the fire at Lick in 2020. They were lucky to escape with as little damage as they had. I'm not minimizing the damage, but it could've been far worse. We have sites that, if humanity survives 1,000 years from now, are going to be looked at with perhaps more awe than the artifacts we find when we go to Rome. These are going to represent turning points in humanity's understanding of our place in the universe. The significance is difficult to overstate. Yet, we're doing so little to really maintain and protect these facilities. Somehow, that needs to change.

ZIERLER: Bringing our conversation closer to the present, tell me about the Zwicky Transient Facility that got up and running last year.

ZMUIDZINAS: This is Shri Kulkarni's brainchild. And Shri has been working in this direction for quite a while. You really need to talk to him to get the whole sweep of the history. But you could say this is a continuation of the very early work that even in the 1980s, I remember seeing happening at Berkeley with the supernova surveys and how that led to the discovery of the accelerating expansion of the universe. When you have a new technology–which at the time in the 1980s was CCDs. CCDs were invented in 1969. That led to a Nobel Prize for the two inventors at Bell Labs, Boyle and Smith, but CCDs were really lousy for astronomy for quite a long time. It was only through hard work, especially at JPL, there was an engineer there by the name of Jim Janesick who worked long and hard, many years, understanding why they didn't work as well as they should and how you could change their design to make them work really well. That ultimately led to CCDs being used on the Hubble, in the WFPC instrument JPL built. All of that early work on CCDs being done at JPL directly led to their use on Hubble. As they were getting better, astronomers were using them on the ground. This was really picking up in the 1980s, so that's what was driving this search for supernovae, the use of CCD cameras on robotic telescopes. The same idea can be generalized. You can make ever-larger cameras.

The CCDs kept getting larger and larger. The computers you need to process the data, the disk drives and memory you need to handle the quantity of data, kept advancing by Moore's law. Over the decades, the ability to survey large areas of the sky kept getting better and better. You could look for ever more rare events. You could image big areas of the sky and ask the question, "What's different from last night? What's new in the sky?" And that's what ZTF is doing. It's imaging large portions of the sky. It has an enormous field of view, some 50-square degrees. Something like that. It takes images of big chunks of the sky every night, and it finds what's new. As a result, it's able to find new kinds of supernovae, and lots of other stuff. They've been discovering that the phenomenology of supernovae is a lot more rich than was previously known. It's opened up, you could say, a whole new branch of astronomy as a result. And it's fundamentally technology-driven. This is a direction that Shri has been pushing now for quite some time. And really, in the US, he and his ZTF project are at the forefront in this area. There's a huge project coming, which is the Rubin Observatory, previously known as LSST, the Large Synoptic Survey Telescope, which is being built in Chile, and that's going to be an even larger camera on a much larger telescope, an eight-meter telescope. It's going to be much more sensitive, and sooner or later, when it comes, it's going to certainly supplant ZTF as the fastest and most sensitive survey telescope of its type. But I think ZTF and Shri's team will have done very well to make a number of discoveries by getting there first.

ZIERLER: Bringing our conversation right up to the present and circling back to our initial conversation, in your position now as director of COO, are you feeling the pull back to submillimeter astronomy, that that's something you need to be more involved in at some point in the future?

ZMUIDZINAS: I'd say I'm thrilled to see the opportunity for a far-infrared probe with NASA. I'm thrilled to see JPL taking it very seriously and NASA taking it very seriously. I attended an initial science workshop last week for the far-infrared probe, and I was absolutely thrilled to see the number of people, the number of scientists attending, the wide range of people and ideas. I'm very excited about the prospects. We have our Caltech protegees leading the charge. It's Jason Glenn and Matt Bradford, whose names I mentioned. Jason is serving as the principal investigator, and I'm not quite sure of Matt's title, but he's the chief ringleader at JPL for this. I'm really thrilled to see that, and I really hope that project goes forward. If it goes forward, it's going to offer, compared to the Herschel Space Observatory, an improvement in sensitivity over a factor of 1,000. It's just an incredible advance. Instead of talking about detector arrays where you have a few hundred detectors, we're going to be talking about detector arrays that are potentially approaching 100,000 pixels.

So that's maybe not quite a factor of 1,000 improvement in the detector count, but certainly a factor of 100 improvement. A factor of 100 more detectors where the detectors individually are 1,000 times more sensitive is just a transformational advance. I'm really hoping that project can go forward. It would be a spectacular application of these kinetic inductance detectors. That really would be wonderful to see. But I spoke with an important person at JPL named Jeff Booth. He's involved in the Astronomy and Physics Directorate. He essentially runs the formulation of new astrophysics missions at JPL. He's the person whose job it is to make sure that JPL puts their best foot forward in terms of a proposal to NASA for a far-infrared probe. That means wrangling the best people to work on this project, making sure they have the funding they need, making sure that they understand what NASA's doing. It's a big, important job. I spoke with Jeff shortly before Christmas and told him I'm interested in helping this probe in whatever way I can. But I asked him not to give me a real job because by the time it flies, I'll be over 70. [Laugh] "Don't count on me to be doing a real job by that point."

ZIERLER: I have one final question to wrap it all up. The question will have both retrospective and forward-looking aspects. Looking over your career, a word that jumps out at me is eclectic. It's very hard to pigeonhole you both in terms of the kind of science you've pursued and the ways you've looked to apply it. My question is, to what extent is that generational, and to what extent are students today looking into the future for their careers, where things seem so much more specialized now? Is the path you took even possible today for graduate students and post-docs?

ZMUIDZINAS: I think of myself as primarily an experimental physicist. I'm interested in making measurements and finding ways to improve how the measurements are made. That explains my involvement in detectors, instruments, and so on. Astrophysics is an interesting setting to be making measurements in. The measurement challenges are difficult, and what you get for improving the measurement, I find to be very motivating. I find it very motivating to be able to study the universe at a sensitivity that's not been possible before because it opens up the possibility of discovery, of learning new things. I'm motivated especially by the unknown, by what lies beyond what we can think of. All of these astronomy projects have to have a science case, an explanation for what science the project might be able to do. All those science cases are constructed by taking our existing understanding and trying to extrapolate it, saying, "Given what we know, what kinds of things might we be able to see and learn?"

But what is missed entirely are the things we can't think of. And experience has shown that human imagination, however wonderful, is also very limited. If we simply had a better instrument with which to look at the universe, what are the things we'd discover that we have no idea how to predict? That, to me, is the most exciting thing, the unexpected discoveries. The chance to open up new possibilities and realms of discovery is, to me, the most motivating thing. When I think about the kinds of things I've worked on over my career, that's basically been the motivating factor. How do we get to the next rung on the ladder? How do we open up new discovery space? It hasn't been focused on a single science question because in my view, that's too narrow a focus. I think from the kinds of things that, at least when I was younger, I had some skill at, the kinds of things I liked to work on, detectors and technology, any scientific opportunity those skills, techniques, or technologies could be applied to was interesting, whether it was galaxies, or helping out with cosmic microwave background measurements, or looking for water in nearby star-forming regions. It's all interesting, it's all fun, it's all fair game.

ZIERLER: For students looking to the future, is that an advisable approach, what you were able to accomplish, how you were able to accomplish it? Is the infrastructure there to pursue a similar path?

ZMUIDZINAS: That's an interesting question. I'd probably answer that with yes and no. This was some years ago. My former graduate student advisor, now Nobel Prize-winner, Reinhard Genzel, was visiting. For some reason, we were down in the Rathskeller in the basement of the Athenaeum, and I was there with some of my students, probably former students at the time. One of them was Frank Rice, who now runs the undergraduate physics labs at Caltech. Reinhard was there, I think just having dinner. He had probably just come in and was going to be visiting Caltech, so it was a random accident he was there. But of course I recognized him, and we started talking. I think Reinhard opined at that time, which was maybe ten years ago by now, that essentially, I was a dinosaur, that my career path didn't exist anymore in astronomy, that the future involved people who could simply take data from observatories and write papers. Which is a lot of what observational astronomers do. That it was becoming too specialized a field. And there's a lot of truth to that. When you look at instrumentation projects for Keck or TMT, they're very large undertakings.

The idea that you can somehow play a substantial role in the development of one of those instruments, and by substantial, I mean a deeply technical role, and at the same time, succeed as a faculty member at a place like Caltech, I think, continues to be challenge. But you look around at our faculty, and you see people doing it. You see people like Dimitri Mawet, who is as deep in the instrument technology as he is in the exoplanet science. You see Andrew Howard building the Keck Planet Finder. My judgment of Andrew is that he may not be quite as deep on the instrument side as Dimitri is, but nonetheless, he's pretty deep. The only way astronomy's going to advance is to improve the tools that we use for doing it. The question is, how does that translate to a faculty position? What should a member of the Caltech faculty be focusing on? I think the answer, to a large degree, has always been science. Focus on the science. I think that's a good answer for most of the faculty. But I think there always will be room for people who come at it from a different angle.

ZIERLER: Jonas, it's been a great pleasure spending this time with you. I'm so glad we were able to do this, to capture all of your recollections and insight. Thank you so much.

ZMUIDZINAS: It's been a fun trip down memory lane, and I'm glad you led me down it. Thank you.

[End]