James P. Eisenstein, Condensed Matter Physicist

There is universal agreement that one of today's most exciting fields in physics is condensed matter. From his pathbreaking investigations on the properties of superfluid helium, to his more recent efforts applying experimental research to quantum science, Jim Eisenstein has been a central player in these developments.

Eisenstein grew up in St. Louis and he attended Oberlin as an undergraduate. At Berkeley, his research on superfluid helium yielded foundational results on the properties of helium-3 and its relevance for superconductivity. After a brief time at Williams College, Eisenstein moved to Bell Labs, which was a leading center in research on the quantum Hall effect. Eisenstein's experimental results in the field laid a foundation stone for what is now known as topological quantum computing.

Among Eisenstein's many honors are his election to the National Academy of Sciences and being named a Fellow of the American Physical Society. In 2007 he was the recipient of the prestigious Oliver E. Buckley Condensed Matter Prize, "for fundamental experimental and theoretical research on correlated many-electron states in low-dimensional systems."

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Thursday, December 23rd, 2021. I am so happy to be here with Professor James P. Eisenstein. Jim, it's great to see you. Thank you so much for joining me.

JAMES P. EISENSTEIN: Nice to see you. You're welcome. I'm looking forward.

ZIERLER: Jim, to start, would you tell me, please, your title and institutional affiliation here at Caltech?

EISENSTEIN: I am what's called the Frank Roshek Professor of Physics and Applied Physics, Emeritus.

ZIERLER: Jim, when did you go emeritus?

EISENSTEIN: Officially, I think three years ago, just about now, late 2018.

ZIERLER: What were the circumstances of you deciding to go emeritus at a relatively young age compared to so many of your colleagues?

EISENSTEIN: That's a complicated question. The circumstances were primarily that Caltech—(a) I was interested in retiring for some time, and Caltech, like many institutions, has an incentive program, to some extent, if you retire below a certain age. I think that age is 68, although I'm not positive. They may have changed the rules. The incentive is that they give you a couple years prior to your actual retirement in which you no longer have any teaching or committee responsibilities. There is a small, a relatively small financial incentive as well, but the main incentive was that I could take a couple of years, and sort of close—finish up some loose ends in the lab by myself. I'm an experimental physicist, and I had an active group, a small but active group for the preceding 20 years or so. But I wanted prior to retirement to actually go back into the lab myself and do some work, which I did for almost three years. It really came to an end, I guess—two years, really. It came to an end—let me see if I can figure this out. Actually, I said something slightly wrong. I did retire at the end of 2018, but this two-year period of no responsibilities began two years prior to that. During that period as well as the subsequent time before the pandemic came, I worked in the lab alone, which is something I wanted to try to do again. I'm a very hands-on scientist. Although I enjoyed very much having good students and postdocs, I always sort of missed actually making the discovery late at night myself instead of only vicariously through students. So, I did that for a few years, and enjoyed it quite a bit.

ZIERLER: Jim, what were the research questions that you were after during this special opportunity all by yourself?

EISENSTEIN: Well, they were obviously continuations of work that had been done in the lab for many years. I worked on something called low-dimensional electron systems, which are collections of electrons which are in semiconductors in general confined in some way to less than three dimensions. I worked on two-dimensional electron systems, broadly speaking, and wanted to extend some measurements that we had done that had some interesting sort of suggestions that we hadn't had time to follow up with my students. So, I did that, and it worked out pretty well. I had a good time doing it.

ZIERLER: In what ways have you remained connected to Caltech since your retirement?

EISENSTEIN: Since retirement, again, I spent a couple of years up to the pandemic being about as active in the lab as any graduate student, and you can ask my wife that if you don't believe me.

ZIERLER: [laugh]

EISENSTEIN: It was true, I worked very hard in the lab. But the pandemic, of course, kind of put a crimp in everything, and I didn't want to go in for quite a while. As time went on, I actually slowed down my research pretty precipitously, and am no longer active in the lab, at least at the present time. There's some chance it'll resume, but I would say it's probably a little probability.

ZIERLER: And probably the longer the pandemic grows—grinds on, the lower that probability gets.

EISENSTEIN: Absolutely, yeah. I don't need to say something that's totally obvious to everyone. The pandemic has changed everybody's lives in big ways. Prior to it, like everybody else in science, I had many opportunities or actually invitations to go to conferences around the world, which is basically something scientists do when—do a lot, and all of those came to a halt. There were many cancelations, and it just seemed like a time to—that (a) I was retired, and (b) there was this pandemic slowing everything down. Maybe I could find other things to do that didn't involve the lab. So, I'm connected to Caltech but loosely these days—mostly to the swimming pool.

ZIERLER: [laugh] Jim, not being at the lab, not going to conferences, what opportunities does that give you with expanded bandwidth in terms of the literature, in terms of your other interests? What have you been doing for the last year and a half?

EISENSTEIN: That's a good question. There's no difficulty, if you desire, in maintaining connection to the forefront of research, through the journals and online seminars. They go on pretty much the same as they did before, only they're all on Zoom now. So, there's really no problem if you want to do that. The thing that's lacking, and it was central to the way I did research, is the personal one-on-one discussions with students and other researchers, theoretical physicists like Bert Halperin, for example, that are no longer possible. You can do Zoom until you're blue in the face.

ZIERLER: Yeah.

EISENSTEIN: But it's just not the same.

ZIERLER: Right.

EISENSTEIN: For someone who—like myself—who is at the end of their career, it's just irreplaceable. Even just the lunchtime conversations at conferences, they're all gone. So, that really changed things, I think, for me in a really deep way. I suppose young people that are just coming up now, well, this is the world they live in. They'll adapt to it, and they will do their work that way. But it was a tremendous loss for me—

ZIERLER: But of course—

EISENSTEIN: —to not have the personal contact.

ZIERLER: —there's a physicality of being in the lab that cannot be replaced, even if you're just starting out in your career.

EISENSTEIN: Well, there's that, true. That's certainly true. [laugh] I've been around a long time, and I have certain ways of doing research, and they're not the ways that young people do research anymore, and my work was very—it was automated at some level, but it was not something where—I couldn't dream of doing my experiments on my iPhone from a remote location. It's inconceivable to me that if I'm not there—I used to always stress to my students that—they would take a lot of data, but they wouldn't be there sort of watching it coming out because it comes out slowly and just things are going on. I always felt that you had to interact with your experiments on a continuing basis, physically, as you point out so that you could make the course corrections and have the understanding of things that were happening in real time. Storing it all up in a hard drive, and looking at it later, that's not the same—not for me, anyway. So, it's a very—

ZIERLER: Jim, how much of that is about tinkering and instrument-building and calibrating in real time?

EISENSTEIN: There's a lot of that. I was, again, old-school. We built everything. We calibrated everything ourselves. We understood how our instruments worked. Not that students don't, but they rely much more on packaged instrumentation that we didn't—well, certainly, when I was a student, it was utterly unavailable. Because the way you do things, it's sort of baked into you when you're young, I wouldn't—I would continue to work in that mode, in other words, understanding my—repairing them myself, for example, when they broke; not standing there and saying, "It's broken. What do I do? Call up the service department." That was just inconceivable. It just didn't work that way. So, the lack of that, being in the lab, changing the knob in real time because you knew it was time to do that, rather than being remote, was—I just couldn't imagine doing it remotely. So, when the pandemic came, and I was out of the lab, the lights went out. That was the end of the experiment.

ZIERLER: Jim, has this increased your interest in theory at all, just being home and reading and looking at it from a different perspective?

EISENSTEIN: I don't think so. I always had a strong interest in the theoretical side of the research that I did. I was not a theorist, but I always paid very close attention to what the theorists were up to. Oddly enough, most of the contacts that I have outside of Caltech, even ins…well, even inside Caltech, they're all theorists. They're all theorists. I have a few friends who are experimentalists in the same general area. But when I wanted to talk about my experiments or hear about somebody else's work, it was Bert that I talked to. I could give you a long list of other distinguished theorists. I think if you ask people—I'm not sure—but I think if you ask people in the outside if I was well-connected to theory, they would say, yeah, too well-connected.

ZIERLER: [laugh]

EISENSTEIN: I value that enormously because I could do things in the lab that theorists could never do. But, on the other hand, they can do things that I could never do. I really relied on them to a great extent to have the stimulating discussions about what was going on. It was very important to me.

ZIERLER: Jim, some broad-range questions about your fields of research and historical perspective. First, a generational question. Was it always condensed matter, or are you old enough where it was solid-state, at least maybe in graduate school?

EISENSTEIN: Well, that's a good question. I remember the day I got a job at Berkeley as a graduate student in a research group. A professor, a guy named Richard Packard, looked at me, and he said, "Are you sure you want to do condensed matter physics?" I had never heard that expression before because it was always solid-state physics. Now, what's particularly funny about that is that his research—and what I ended up working on for my PhD thesis—was with liquids, [laugh] and there were no solids.

ZIERLER: Yeah. [laugh]

EISENSTEIN: [laugh] It really was condensed matter physics that I started doing. But I came from the—I'm old enough that my education was back when we had transistor radios and solid-state physics, and condensed matter was a newfangled term that we used to kind of embrace the larger [field]. So, yeah, I'm old enough to remember solid-state. I even learned—I even know about vacuum tubes, if you really want to—

ZIERLER: [laugh]

EISENSTEIN: —if you want to go back some time.

Theory and Experiment in Condensed Matter

ZIERLER: To go back to the interplay between theory and experiment in condensed matter, it's such a phenomenal relationship in the way that the field has advanced—

EISENSTEIN: Yeah.

ZIERLER: —in terms of this interplay. In terms of decades or generations or however you think about it, when have the theorists been out ahead of the experimentalists, and when have the experimentalists been out ahead of the theorists?

EISENSTEIN: Well, the glib answer is the experimentalists are always ahead of the theorists. That's not fair, but there's a lot of truth in it too. Today, there's a lot of theory, and there's a lot of—you're going to get me philosophical—but there's a lot of experimentalists chasing theory. If you—and, again, I'm an old guy, so I can say, well, that's not the way it should be. I can look back in history, and I can tell you with good examples that the big things haven't been that way. Take superconductivity. That's the old example. That's 100 years…110 years old now. This was just because some guy in Leiden University had this machine to make things really cold, and he was just fooling around, and made the biggest discovery in condensed matter physics of the last 100 years, no question about that. Same thing with the—much more recently—but with the quantum Hall effect, and the fractional quantum Hall effect. No theoretical suggestions, nothing. All came out of the lab. Transformed condensed matter physics, both of those events. All of those events transformed the field. So, in those cases, high-temperature superconductivity, which is not a field I work on, but, again, it was driven by experiment, and theorists are still trying to catch up with the experiments there. Now, things have changed a little bit, and they've changed in ways that haven't really meant a lot to me but certainly to others. One is the advent of something called topological physics, which really, if you think about it, is the outgrowth of the quantum Hall effect.

ZIERLER: Yeah.

EISENSTEIN: That's really where topological ideas in condensed matter physics got started.

ZIERLER: Jim, I wonder on a technical level if you can explain that.

EISENSTEIN: Yeah, I can explain that. That's actually not so hard. The quantum Hall effect, in fact, this is something that Bert had a tremendous role in. He was maybe—no, certainly, not the only one, but he was one of the big players. In a quantum Hall system, it's again what's called a low-dimensional electron system. Just think of a tabletop covered with electrons [laugh], and they're running around, repelling one another, doing things. A big magnetic field is present. What we learned was that under certain circumstances, this system could become an insulator insofar as you couldn't get electricity to flow through the bulk. So, say if I have a circular table, I couldn't get electricity to flow from the interior to the outside. It was just an insulator. But at the outside edge, it was a conductor. It was a conductor. If you tried to put two wires on the outside edge, that would drive current from one to the other—but not if you went into the inside. If you went into the inside, it was an insulator. This was the discovery of what are now called topological insulators. They are materials which are, in the bulk, they're insulators, just like regular—like glass. But at the surface, they have these conducting channels, we call them. Those channels are invariant. You can't remove them. If you break the thing in half, you'll get two pieces with the conduction of the outside. It's a topological quantity. You can't get rid of it. So, that's what a topological insulator is, and the quantum Hall effect is the first example of that.

People didn't really appreciate that connection to topology right away. But some early theorists—Bert is one. A fellow named David Thouless got the Nobel Prize really for that—I guess in many ways—for that reason. That was a big part of why he got the Nobel Prize. He emphasized the topological content. Now, we find that there are materials—and now I'm out of my depth—all kinds of crazy materials, even three-dimensional materials that are insulators in the bulk but have strange conducting channels on their outside surfaces that you can't eliminate. So, they're like—it's the old—what's the canonical example, trying to explain to a layperson what topology's all about? They always start with a coffee cup. No, they start with a donut, and they bend it into a coffee cup, which has one handle on it. I wish I had—oh, here it is, right here, around my coffee cup. That it's really the same as a donut, it's just they push the inside in. But it still just has one hole, only one hole. So, it's a topological property of the thing that's important. The quantum Hall effect displayed that for the first time that people really appreciated it. Then this grew tremendously in the last 20 years or so. That's where I think the prevalence or the experimentalists following theorists really got going, rather than the other way around. So, that's the one example. The other one, of course, is quantum computation and quantum information, which I have no real connection to from a research point of view any longer. But there, again, the theorists are light-years ahead of the experimentalists because making a quantum computer is incredibly difficult, and nobody's done it really. You don't type on a quantum computer to make this interview, and you won't next year or the year after. So, the experimentalists are long—are well behind that.

ZIERLER: Jim, when you put a hard stop to no longer being involved in quantum computation, I'm curious just generally about your affiliation with the IQI and IQIM, and if there's a story therein about where you slotted in or where you did not, or where you saw the field going?

EISENSTEIN: I don't know. I'm a grumpy old man. What's the thing to say? I certainly had—I was affiliated with IQIM for quite—several years, and certainly in its first funding cycle. I had funding from Microsoft Corporation for about—I don't know—seven years or so because they're very interested in quantum computation, a particular aspect of quantum computation that's very obscure. But my feeling always was that at some—at least for me, the focus of the IQIM was not on the materials side of condensed matter science. In other words, make some crazy material that does some crazy thing, and try to understand it; maybe a crazy thing that's actually useful, if you're lucky—if you're really lucky—or maybe just a crazy thing that's really interesting that theorists will scratch their chins about for a long time, and try to understand. So, the IQIM is—John Preskill will probably get mad at me. But it's I-Q-I-M because there was always an institute—well, not always. But long before IQIM there was IQI. Caltech is a leading institution in the theoretical side of quantum information, and becoming more so, I guess, with this Amazon project. There's a burgeoning experimental side too. But to me it just wasn't condensed matter physics; it was IQI, Institute of Quantum Information. If you could do things related to that in materials then, good, you fit right in. But if you wanted to do things that weren't so closely related, you were still welcomed and always welcomed there, but I always felt like I was not really at the focus of what that institute is all about.

ZIERLER: Jim, in thinking about the gulf in quantum computation between theory and experiment, is one of the challenges simply that existential questions remain about what a quantum computer will be good for?

EISENSTEIN: Oh, I'm out of my depth on that. But my gut feeling is the answer to that's no, that there are known problems that a quantum computer, if we could make one really work, could be wonderful to have. There're known things that you could do. I don't know if you were thinking of sort of the deep puzzles of quantum physics or whether that's the issue or not. I would say no. I'm (a) uneducated in that field, and (b) unappreciative of the deeper puzzles of quantum physics because they never seem to really affect physics on a day-to-day basis. I don't know if that's what you were referring to.

ZIERLER: Yeah.

EISENSTEIN: Like the kind of stuff that's—and wave function collapse across the universe and things like this are very deep questions but—I don't know—they don't have any impact on me or research on a daily basis.

ZIERLER: Jim, on those deeper questions, quantum computation is obviously one application. For you and your overall research agenda, when is it about the basic science, and when is it about thinking about possible applications or society—societal usefulness?

EISENSTEIN: Good question. I've never troubled myself with societal usefulness, and one can criticize that, without question. You can certainly criticize that. I rely on the historical precedent that, sooner or later, it's going to do something important. Again, I always go back to the example I like the most, and I stressed very heavily too when I was on the National Research Council panel reviewing condensed matter physics some years ago, that superconductivity is the best example you could ever give of something which, at the time it was being discovered, must've appeared to be just preposterous research. Who in the world would ever want to cool something down to such a low temperature that you could have no—there's no use for this. Kamerlingh Onnes, what are you doing with the money that we gave you? This is ridiculously wasteful. Now, in the last 30, 40 years, it transformed medical diagnostics.

ZIERLER: Yeah.

EISENSTEIN: It transformed it. Onnes had no inkling that that would ever happen; no one did. There was no way, no logical way to go to draw a line ahead of time between those crazy discoveries and that application to medicine. So, there you go. That, to me, that's the poster child for doing curiosity-driven research. The stuff that I've worked on over the years, although my own interests are in the very abstract side of the field, being that I relied on materials, extremely pure crystals grown by the world's experts in crystal growth, those materials at the same time have enormous usefulness. One could argue, I think pretty persuasively, that advances in making those materials more and more pure, and with greater and greater definition, and more and more complexity, has had a clear impact on electronics. Fast transistors are designed and built in a way that relies on the same technology that I used for samples that exhibited exotic physical effects. So, that's not a cause and effect, but it's a parallel development that you could argue maybe wouldn't have—I mean, maybe the basic science has been the bigger beneficiary, but clearly, they're related to one another.

ZIERLER: And it's always hard to see where these things are going.

EISENSTEIN: Yeah, I think it's a fool's errand to try to predict these things in advance, and people don't have patience with that argument, and I understand that, but anyway.

ZIERLER: Jim, just some mundane questions as they relate to your title. First, who is or was Frank Roshek?

EISENSTEIN: I don't know.

ZIERLER: [laugh]

EISENSTEIN: I don't know.

ZIERLER: I googled him. I couldn't find much online.

EISENSTEIN: Come on, he was somebody who donated money to Caltech, whether he had a connection—he must've had some connection. His estate—as I understand it—his estate gave enough money to endow a professorship at Caltech, and I was the first. I think I was the first Frank Roshek professor. Who this guy was and what he did was never made—you might've argued that, sooner or later, you're going to have to have lunch with the donors. It never happened. One day, I got a letter from the provost, and that was that. So, Caltech, for obvious reasons, would like to find donors to support their faculty. It takes the burden off of them of finding my salary. But who Frank Roshek was, I'm afraid I don't know.

ZIERLER: Ongoing mystery.

EISENSTEIN: Yeah.

ZIERLER: You have faculty pages both with EAS and PMA, and your title is physics and applied physics.

EISENSTEIN: Right.

ZIERLER: Is that a joint appointment? Do you—

EISENSTEIN: No.

ZIERLER: —report to two division chairs? How does that work?

EISENSTEIN: No, it's purely a courtesy appointment to applied physics. I was hired by physics, by PMA in 1996. Somewhere around 2000 or 2005—I don't remember when it was—I asked the people in EAS if I could have this courtesy appointment, thinking, erroneously, that it would be important in recruiting graduate students.

ZIERLER: Why? What were the trends at the time that made that sound like a good idea?

EISENSTEIN: Oh, I don't think I had my ear close enough to the ground. I just thought—and, actually, I do run across this: students wondering in advance, "Am I going to be able to move transversely in the—if I come in as an applied physics student, does that mean I can't work on LIGO, for example?" The answer's, no, it doesn't matter. You can—if you find an advisor who's willing to hire you, it can be biology. It may be more difficult to do that, but between physics and applied physics the membrane is totally permeable.

ZIERLER: Yeah.

EISENSTEIN: So, in the end, I don't think it had any impact on my ability to find good graduate students. It turned out they were all from PMA in the end. I never had one who came through applied physics. But that was the motivation for me asking for that, which they graciously said sure. It was no big deal. But I don't have to—there were no teaching responsibilities or any other aspects of that. In retrospect, it probably was—it was unnecessary to do it. But it didn't really hurt anybody, I don't think.

ZIERLER: Jim, the idea of there being no wall essentially between applied physics and physics, to what degree can we extrapolate that for Caltech as a whole, just its flatness, the sense of adventure that allows for a multidisciplinary approach to these things?

EISENSTEIN: I'm not too knowledgeable about that. But I would say that if you're a good, smart person who can impress a thesis advisor, you'll get a job.

ZIERLER: Yeah.

EISENSTEIN: I don't think there are particular administrative or any other kind of bureaucratic reasons why you can't make that change. In reality, I think if you want to do it, and you've got somebody who wants to take you, bingo, it's going to happen. I'm not aware of what it's like at other institutions, but I have a hard time believing that at a good place, obstacles would be put up to prevent that. Now, there's another—there's a related aspect of that; that this wasn't always true—not that the students couldn't transfer between EAS and/or applied physics—let's not call it EAS; let's talk about applied physics—and physics. One could ask the question: why was there ever an applied physics department? What are they doing that's so different than what I was doing? The answer is nothing.

ZIERLER: Well, isn't this where we get to Murray Gell-Mann and squalid-state?

EISENSTEIN: Yeah, that's right. So, you know that story, and that was a—Caltech was by no means the only place that had that disease, but we had it, and it's gone. It's utterly gone, as far as I can tell. It's been gone as long as I've been here.

ZIERLER: Well, not only that but isn't—I'm going to offend a lot of people. But condensed matter, in some ways, there's a lot more exciting stuff going on than there is in particle physics right now.

EISENSTEIN: Well, I don't know whether I want to join you getting beat up about that, but I would certainly agree. Condensed matter physics is unbelievably vibrant. It's just unbelievably vibrant. It's more vibrant than it was when I started in it. You go to the March Meeting, the APS meeting, and there are 12,000 or 15,000 people there from all over the world, and there's so many—so much stuff going on, you can't believe it. So, yeah, there's a lot of—and a lot of it—there's plenty of applied work going on, but there's also plenty of pie-in-the-sky stuff that even I find to be just too far [laugh] out in space. It's a very fundamental—there are very fundamental questions being asked in condensed matter physics that have kept the field as vibrant as it can be.

Condensed Matter and Limitless Frontiers

ZIERLER: Jim, is part of that is in condensed matter, there isn't a Standard Model that everybody is continuously trying to break out of and cannot? Are the frontiers simply much bigger at this stage in the game?

EISENSTEIN: That's a good question. [pause] Materials are complicated, and you have 92 elements, and you can make all kinds of chemical combinations of those elements, and bazillions of materials come out of that. We are still lacking an understanding of all the possible things that can appear, and that's what drives the field. So, I would say the complexity is much higher. It doesn't mean the problems are harder, because I don't think they necessarily are. But there's an infinitude of them [laugh], and there will always be more. Take this issue of topological insulators or topological matter. You can ask, how is it possible that someone like myself, who got an education in the '70s, still thought that nature—that materials—came in three types? There were insulators, there were metals or conductors, and then there were semiconductors, which are really just insulators that you could fiddle with if you put in impurities. That's all there was, basically those two classes. Then, all of a sudden, it turns out that in the last 20 years, or really 40 years if you want to go back to the very beginning of the quantum Hall effect—again, the appreciation was not there at the beginning—that, no, actually, there are materials which are both conductors and insulators, and topology plays a big role. To me, it's astonishing that no one—I mean, there were some very big heavyweights in the theoretical side of condensed matter and solid-state physics. The John Bardeens and people like that, Conyers Herring, these guys, they had no idea. It wasn't that they weren't smart enough. But, all of a sudden, it turned up, this whole new connection.

ZIERLER: Jim, what have been some of the technological developments that have allowed for thinking about these new materials?

EISENSTEIN: There's I guess two things, I would say. I'm speaking off-the-cuff here. I haven't deeply thought about this. But there's two sides to that, I would say. One is obviously material synthesis. We're way more sophisticated than we were 50 years ago. We can grow exotic things that you could never dream of making—not that you couldn't mix chemicals together. Anybody can do that. But what came out was garbage. Getting it to come out to be beautiful and pristine, and have the purity levels that you want, to do something fundamental was impossible. It's not anymore. With the advent of things like molecular beam epitaxy, which is the technology that I rely on or used to rely on for my samples, that didn't exist 50 years ago. When people said they were going to do molecular beam epitaxy, a lot of people just laughed at them. That'll never work. That will never work. Well, it works. So, that's one side. Material synthesis is a big part of it. We can make things we could never make before. The other is we have tools, laboratory tools that we never had before. Probably the best example of that is the tunneling microscope. We can see things we didn't used to be able to see. I remember growing up as a child, and I was very interested in science. But one thing I knew that was true is you can't see an atom. I carried that around as a child.

ZIERLER: Yeah.

EISENSTEIN: You don't see them. They're there but you can't see them. Well, that's false. [laugh] That's no longer true. You can see them. So, there are a lot of tools that have become available that we didn't—and those are the cheap ones. I'm not talking about the big things like the big neutron sources and stuff like that that we didn't used to have. So, we have tools we didn't used to have.

ZIERLER: Jim, what became of your lab? Who inherited your equipment?

EISENSTEIN: I still have it. It's only been since the pandemic that it's been quiet. In fact, I went back when we had the brief false spring, you know, last spring?

ZIERLER: Yeah.

EISENSTEIN: I went back and started up in the lab again. Then I did an experiment. I did what I call an experimental run, and then shut it down again. So, the lab is still there. That's a delicate question. What's going to happen to that? I don't know.

ZIERLER: How was your muscle memory when you went back in?

EISENSTEIN: Pretty good. That stuff's baked into me. It's like riding a bike.

ZIERLER: Yeah.

EISENSTEIN: I can transfer liquid helium just like I used to.

ZIERLER: [laugh] That's good. [laugh]

EISENSTEIN: Yeah. I'm not—look, I'm a little tippy on the ladder now that it's a little frightening for me to do these things because I'm older. But I didn't forget how to do stuff.

ZIERLER: Is it lying fallow right now? Are there students accessing it?

EISENSTEIN: It's lying fallow at the moment, although I am interested in the work of a new—a relatively new—well, he's pretty new—assistant professor in applied physics. This is Joe Falson. He and I are discussing things together. I don't think I'll get involved in his research directly. But I know—we've talked about—he uses some of the facilities that I have occasionally. I have an electron beam writer and some microscopy facilities. He used some of my cryostats for a while. So, it's not completely—and he's borrowing stuff at a good rate. It's going out the door and going across to the other side of campus. But at the moment, the lab is quiet.

ZIERLER: Yet more reason to hope the pandemic is over and, if you want to, you can get back in.

EISENSTEIN: Yeah, right, it's—you're far too young to understand the difficulty, what retirement is all about.

ZIERLER: Sure.

EISENSTEIN: I don't think anybody really understands it until they try it. Once you try it, you got to start thinking about a lot of things. I'm away from research at the moment. I won't say I'll never do it again. But I think the probabilities are getting smaller as the days go by.

ZIERLER: But it's a totally different culture when you use the word "retirement". It's not like 30 years at the end of an insurance company, and they give you a gold watch, and now you go home.

EISENSTEIN: But they never gave me a gold watch—

ZIERLER: [laugh]

EISENSTEIN: —I should point out. That's something that still—that actually still rankles a little bit—

ZIERLER: [laugh]

EISENSTEIN: —you know, some functional equivalent of the gold watch. But, yeah, it's not the same.

ZIERLER: But, look, scientists love what they do, and you never really fully walk away from it. I've found that. Even if you're not in the lab, there's always a connection. There's always the curiosity. The interest doesn't go away.

EISENSTEIN: Yeah, that's true. I think it depends a lot on the person. I think one of the things—I mean, I miss two things about it. If I had to say, what do you miss about working in the lab, one is working in the lab. It's hard work. It's harder now than it used to be for me because I'm older. Believe it or not, there's a physical aspect to it. Going up and down the ladder 50 times a day is something that's harder than it used to be. But the main thing I miss about it, actually, is the collab…not the collaborations but the consultations and the meetings with people around the world. It's a very nice community.

ZIERLER: Yeah.

EISENSTEIN: With the conferences all gone, that's over at the moment, and I really miss that. I really, really miss that.

ZIERLER: And there's science that's been missed as well.

EISENSTEIN: I think it's inevitable that scientific productivity has suffered. I'm sure there'll be people that say, "No, we just kept cranking along." I don't believe it.

ZIERLER: Well, Jim, that's enough gloomy talk and retirement and all the rest. Let's go back to the beginning.

EISENSTEIN: Sure.

ZIERLER: Tell me about your parents first.

EISENSTEIN: My parents, wow. So, my parents—my father was a doctor; grew up in a small town in Southeastern Missouri. My mother was a homemaker; grew up in a small town in Indiana. My dad, his career advanced to the point that he was a professor of medicine at Washington University in St. Louis, and one of the more senior doctors in the hospitals there, Barnes Hospital, a Jewish hospital in St. Louis.

ZIERLER: What was his field?

EISENSTEIN: He was in endocrinology. He was an expert in diabetes in particular. So, we grew up with science baked into us, pretty much. It was in the '60s that I was growing up. It was just post-Sputnik. Science was really fashionable then in a way that's it not now.

ZIERLER: Yeah, yeah.

EISENSTEIN: For a kid, the idea of building a radio down in the basement was, to me, the most exciting thing I could do. Tearing apart my mom's toaster was just—that was cool, and that's gone. It's changed completely. But, anyway, we had a very nice—I had a very nice childhood. Both of my brothers are scientists. My older brother Bob is a physicist, a retired physicist. Worked for various universities and also for the National Science Foundation. He's involved with LIGO a little bit—still. My other brother is a biochemist at the University of Wisconsin. He's not retired yet. One of my sisters is an epidemiologist. She's retired. My other sister is in public health. They're all retired except for me—I mean, except for my younger brother. So, there was a lot of science in the family.

ZIERLER: Five for five in science at some level.

EISENSTEIN: Yeah, five for five, exactly right.

ZIERLER: Did your father involve you in his work? Did you have an understanding of what he did when you were a kid?

EISENSTEIN: Not really. He was a doctor, so he would come home with doctor stories, and I would hear them at the dinner table, not understanding what he was talking about. But not so much research stories. Research is hard to talk about with people who aren't researchers.

ZIERLER: Yeah.

EISENSTEIN: It's always hard. But doctor stories, that's a human being we're talking about with some disease. He would be on grand rounds or something like that, and he would come home with some story that would turn your blood cold about what was going on in the hospital. But he did—I did go to his lab occasionally, and fiddle around in there, do terrible things to mice, which I still regret. [laugh] But it was just an environment where science was regarded very highly. I should add, by the way, that I disappointed my father continually. I was a terrible student until I grew up. I was a pretty horrible student. [laugh]

ZIERLER: How do you define "growing up"? High school, college?

EISENSTEIN: It was college. Yeah, it was college.

ZIERLER: Jim, either officially or not, growing up in St. Louis, how segregated was your neighborhood or your larger environment?

EISENSTEIN: Totally, it was totally segregated, I mean, come on. It was totally segregated. It was not only segregated racially but of course it was segregated economically. There were more African Americans in St. Louis than there are in South Pasadena, as a fraction, by a lot. There's a substantial African American population in St. Louis. But they weren't on my side of the fence. There's no hiding that. I grew up as a privileged white kid in a small community outside of St. Louis that happened to have a pretty good si…in our little neighborhood, pretty good-sized Jewish community, which is another subset of this larger, much larger white community. So, yeah, it was segregated.

ZIERLER: Was your family Jewishly connected? Did you belong to a synagogue?

EISENSTEIN: That's a good question. I think we did but I think it was not serious. It's never been a part of my life that I've regarded as important. Although my parents, on occasion, would rail about it, they didn't really think it was important either, when you got right down to it. So, I never had a Bar Mitzvah, for example, neither did either of my brothers, and my sisters didn't have Bat Mitzvahs. So, there was very little active religiosity in our house.

ZIERLER: Was it a good math and science program in high school? Were you into that?

EISENSTEIN: I should point out, by the way, that after two years at a suburban St. Louis high school, I moved to Long Island.

ZIERLER: Oh.

EISENSTEIN: My dad took a job in the New York area, and so I transferred to a different high school, where I met my wife, incidentally. I like to—one of our standing jokes is that my grades went up enormously when I moved to Long Island. Why was this? [laugh] I like tell her it's because the standards were so much lower.

ZIERLER: [laugh]

EISENSTEIN: Which I guess is an oversimplification, but there was a little bit of truth to it too. I think the science education that I got at St. Louis in that little, as you say, segregated high school was quite good. Remember, you got to remember what the time was, is that this is the mid-60s. Physics was undergoing a big—at the educational level, there was something called the—what was it called? PSSC? There was some program, and I had physics as a freshman in high school. Then again, later, when I got—if I'd stayed in St. Louis, I would've had it again as a senior. But every kid took what fundamentally was a physics class. They called it quantitative science. It was to learn how to think about things quantitatively, and the things were almost invariably physics related. It was a very good course. So, I had a good education there. Then I got to this school in Long Island, and I took chemistry and physics, and they were perfectly serviceable courses; nothing wrong with them—nothing wrong with them.

ZIERLER: What kinds of colleges were available to you, both academically, financially, geographically?

EISENSTEIN: Well, again, my transcript went up after a couple of years [laugh], but it wasn't exactly—it wasn't like kids today. There weren't 5,000 items on my résumé saying what a great person I was, and all the wonderful things that I did. I was just a kid, and I went to high school, and I got pretty good grades, and they got better as I went along. I did OK on the SATs; nothing to write home about but I did pretty good. So, I applied to mostly small colleges, except for a couple of safety university schools, University of Connecticut, places like that, Syracuse University, which I hoped I wasn't going to have to go to. I ended up going to Oberlin College in Ohio; same place my older brother had gone. That was where I got a really first-rate education.

ZIERLER: In 1970, the '60s must've been going real strong at Oberlin.

EISENSTEIN: Oh, yeah. Oh, yeah.

ZIERLER: What was it like? What were the various movements?

EISENSTEIN: Well, there was—I mean, what we focused on was mostly antiwar [activity] because there was—my wife and I from high school went down to Washington, D.C., for one of the huge demonstrations about the—in the late, I guess, May of 1970 related to the bombing in Cambodia. I think that's what the—I think that was the event that made that. So, Vietnam was at the top of the list. Then, of course, there was Watergate, which turned on a couple of years later, which provided nighttime entertainment at the dining halls. We watched the news every single night in the dining halls to watch what was going on. The civil rights stuff had largely passed by because that was early '60s. My brother was heavily involved in that because he graduated in '64 from Oberlin, and they were closely involved in the Freedom Rider stuff that you may know about. But I was a student. I took my—I took too much physics and too much math when I was there. But the courses that I took were great; really good.

ZIERLER: You were a physics major?

EISENSTEIN: Physics and math, both. As a sidelight, I went and visited—this last September, I ventured forth with one of my old college roommates, and we went up to Maine and visited one of my professors from Oberlin College, who's now in his mid-90s. I went there specifically to tell him that that was the most important part of my education I had gotten.

ZIERLER: Oh, wow.

EISENSTEIN: Yeah, it was pretty nice.

ZIERLER: Why? Why was it so important?

EISENSTEIN: Because he's the one who really got me started in—I mean, I was always a tinkerer. I told you I was very interested in electronics; very interested in astronomy. I had built telescopes and stuff like that. But he was the first person that invited me into research, and I worked with him all while I was at Oberlin on solar physics experiments. We had a telescope.

ZIERLER: So, Oberlin professors did research?

EISENSTEIN: Oh, absolutely, absolutely. Their focus obviously was teaching. They were premier teachers. But his research, to me, was teaching. That's where I learned how to do stuff. He took me to Kitt Peak National Observatory for two different summers, and we worked with these gigantic telescopes, looking at the sun. We built things.

ZIERLER: What's his name? What's this professor's name?

EISENSTEIN: This fellow's name is Joseph Snider—Joseph L. Snider—and he meant more to me than just about any other educator. There was another one at Oberlin too, a theorist, a guy named Bob Weinstock, who also meant an enormous amount to me. But he was a theorist's-theorist, and we sat around and did math problems. It was fun.

ZIERLER: Did you gravitate more towards experimentation, even as an undergraduate?

EISENSTEIN: Back and forth.

ZIERLER: Yeah.

EISENSTEIN: Back and forth. I did all this summertime and school-year research in solar physics with this professor, the guy Snider. But then when it came to doing my PhD—my undergraduate honors thesis, I said I should do something theoretical, which was—it was probably a stupid thing to do. So, I studied what then was something outlandish for an undergraduate. I studied relativistic quantum mechanics with this fellow Weinstock, and learned about it. That was dumb. That was fun but I think it would've been better if I'd stayed with Snider, and done a little more.

ZIERLER: Jim, how parochial was your physics world at Oberlin? When you were there, the early 1970s, there were so many phenomenally exciting things happening in physics: asymptotic freedom; the November revolution; Grand Unification; Standard Model. It goes on and on and on. Was any of this registering as an undergraduate for you?

EISENSTEIN: A little bit, a little bit. I certainly remember about asymptotic freedom a little bit, and unification, and weak interactions. This was noise going on to me in the background. But we weren't in a position at our level of education to understand what any of this was about, really. There were other professors there—Joe Palmieri, Bruce Richards—who were on the particle side of physics—Bob Warner—whom I could've worked with. But I had this interest in astronomy already, and had built telescopes. So, when this opportunity came to work with this guy Joe Snider, who had this solar telescope, and we were looking at what I thought were—and it was true—very interesting pieces of physics—we were watching the sun vibrate. So, the sun has these normal modes of expansion and contraction, and the surface is just like a balloon in some ways. He had an apparatus for detecting this—very sophisticated for an undergraduate—and I understood it, and helped build it. So, this was right up my alley. It was hands-on. It was astronomy related. It was just I didn't have to—the theory behind the physics was not inaccessible. Grand Unified Theory, what am I going to do with that as a 20-year-old?

ZIERLER: [laugh]

EISENSTEIN: That was ridiculous. So, it was clear that it was—he was the right guy. Plus, he was a very personable fellow, and I liked him very much.

ZIERLER: Do you have a specific memory of thinking to yourself, "I want to go to graduate school. I want to make a career out of this. I might want to be a professor one day"?

EISENSTEIN: No. I'm embarrassed to say I don't think I thought about it very much. I just figured that was what I was going to do. In some ways, I regret that. Not that I haven't had a good career. I've had a great career. It is wonderful, and I did well, reasonably well in it. But I might've done better if I'd looked around. I might have at least been able to tell myself I did look around more [laugh] and think about other things, and I didn't. That's part of my personality. I plan ahead too much. So, I think, yeah, I'm going to go to college, and then I'll go to graduate school. Remember, I had my brother, 10 years older than me, who went to Oberlin, then went for a physics PhD at Yale, working on accelerators. He was doing high-energy nuclear physics, so not really high-energy physics but high-energy nuclear physics. So, I had him as a case example, and he's my big brother. So, I don't know, it just all kind of came naturally. I wish I'd thought about it more, to be totally frank with you. I wish I'd thought about it more. I wish I'd not taken quite so many courses in physics and math at Oberlin because, believe me, that place had a lot of other stuff on offer. I took some literature, but I didn't take history, and now I'm really interested in history. So, I really wish I had done that.

ZIERLER: Did you get any advice in terms of where to apply, who to work with, what kinds of programs to focus on?

EISENSTEIN: For graduate school or undergraduate?

ZIERLER: For graduate school?

EISENSTEIN: I don't recall much. I ended up going to Berkeley. My wife, at the time, was applying for graduate school in geology, and she was also at Oberlin, and graduated with a degree in geology. We said, "Well, we want to go to the same place. That's important." Because we got married in high school, so—I mean, not high s…college. I got married late in college. "Let's go to the West Coast. We haven't been there." So, we applied to three schools. It's not like today, it's ridiculous. But we applied to three schools: Stanford; University of Washington was kind of the safety; and Berkeley. We got into all three of them. I don't know why we decided. I think the financial aid or the TAs or it was some financial reason to pick Berkeley. But, also, Berkeley was—there was a lot going on there.

ZIERLER: Yeah.

EISENSTEIN: So, I just kind of fell into that because it was sort of obvious at that time. But I didn't apply to Harvard or any of the places on the East Coast. Barbara and I said, "I don't want to go there." We were just kids.

ZIERLER: Now, were you really—?

EISENSTEIN: I don't regret that, by the way. I don't regret that at all.

ZIERLER: Sure, sure.

EISENSTEIN: I love California. [laugh]

ZIERLER: Were you still open to both theory and experimentation in graduate school?

EISENSTEIN: Yeah, briefly, but I was. A graduate student at Oberlin—excuse me—at Berkeley in my day, you typically didn't get into a research group until you had been there for two years being a TA, and that's what I did. I thought I'll do—I tried experimental high-energy physics the very first summer. I got a job working for a guy named Owen Chamberlain, who won the Nobel Prize in particle physics; discovered the antiproton, or whatever they did. Very nice guy. He was my advisor when I first arrived. A really nice guy. I fooled him. He thought I was smart. I had this guy totally fooled.

ZIERLER: [laugh]

EISENSTEIN: I worked for the group for one summer, and I hated it. I just hated it.

ZIERLER: Particle physics was not your thing?

EISENSTEIN: It was just—well, the stuff they gave me to do was just mindless. I used to like to joke with my wife and other people, but it's not really a joke. They sent me to Fermilab to carry buckets of water.

ZIERLER: [laugh]

EISENSTEIN: So, I did it. I carried buckets of water back and forth. I don't even remember what it was for but I was carrying buckets of water. So, yeah, I didn't—but I then said, oh, I'll do theoretical physics. So, I started working for a fellow named Stanley Mandelstam, a very famous theoretical physicist. Very nice guy too. A little shy. I worked on field theory for some number of months until I one day was trying to figure out some commutator, which was 50 pages long, and I said this is ridiculous. I just—this is not interesting to me, and no way I'm going to be good enough at it to be really good at theoretical physics. I was not that smart. So, I decided to stop doing that. I didn't know what I was going to do. Almost after a year and a half, I was stuck. This guy Richard Packard gave a lecture to graduate students on his research, which was on superfluid helium, and I just fell in love with that. That's really cool.

Berkeley and Superfluid Helium

ZIERLER: Yeah. Why? What about superfluid helium? What spoke to you?

EISENSTEIN: Well, there's the obvious things, right. It goes through tiny cracks without any friction, and it flows out, you know, flows up walls and out bottles. You shine light on it, it goes this way; goes that way. But what really got me was what Richard Packard's sort of—his most famous experiment, I would say—probably most famous experiment, was. He was the first one to photograph something called quantized vortex lines, which have subsequently been rediscovered in the cold atom field. But they started in liquid helium. Liquid helium, in the superfluid state—this is helium-4 in the superfluid state—if you try to put it in a bottle, and start turning, rotating the bottle, it comes into rotation only in a quantized way. It doesn't interact with the walls at all, and sits there. The walls are going around, and it just sits there. Then it says, all right, let's put in one quantized vortex, because the superfluid wave function has to be—has to integrated around some loop. Its macroscopic wave function has to be periodic as you go around this loop. So, you can have one quantized vortex or two or three or four or five up to n. Eventually, it'll look like a regular bucket with a concave surface. But it does it in these quantized steps. This was predicted by—who did this? I don't remember. It doesn't matter. Some theorist predicted this. Maybe it was Feynman. I don't think so though. Packard invented a way to image these things. [unrelated conversation] He found a way to image these things by trapping electrons. Electrons go into liquid helium. They form a bubble. Bernoulli forces make the bubble stick onto the vortex lines like a tornado. It gets sucked into the core. All these electrons line up. Then you apply an electric field, and they come shooting out, and they hit a phosphor screen. It was a brilliant experiment. Lo and behold, they discovered vortex lines. He talked about that, and I just thought that was the coolest thing ever. A very, very difficult, inventive, experimental approach to solve a very fundamental question that really there was a wave function of a macroscopic bucket of liquid that had to be—had to obey some quantization condition, just like the orbits of an electron going around a nucleus have to have a—that's how you get quantize energy levels. It's the same damn thing but it's on a macroscopic sort of millimeter scale. I was fascinated by that. I went to work for him.

ZIERLER: Intellectually, this was not daunting like the theory was?

EISENSTEIN: No. No, what did I—what was the first job he gave me? "Fix the leak detector, Jim. Change the oil." It was stuff that I could handle.

ZIERLER: A car mechanic.

EISENSTEIN: Yeah, a car—yeah, in fact, the best way to get a job in this guy's group was he said—he would interview you, and he would say, "Have you ever built a boat?" I said, "No." He was disappointed. I said, "Oh, but I ground a telescope mirror," and that was good enough. [laugh]

ZIERLER: [laugh]

EISENSTEIN: So, he hired me. [laugh]

ZIERLER: What were the big research questions? What was animating the group at this point?

EISENSTEIN: Superfluid helium-3. I wasn't on the helium-4 side in the end. I had nothing to do with the vortex lines in the end. That was helium-4. Helium-3 is a whole different kettle of fish. It's a fermion, not a boson. The atoms have got three nucleons, not four. So, it doesn't go superfluid at the 2 degrees kelvin that helium-four does. Nothing happens at 2 kelvin. You just keep cooling it down till it just sits there. But people had thought for—I don't know—a long time really since BCS theory of superconductivity that maybe the helium-3 atoms will pair up like electrons do in a superconductor, and form an exotic state. It won't be a superconductor because they're neutral objects, but they'll form a superfluid. People have been struggling to discover this. In 1973, which was the year before I graduated college, superfluid helium was discovered at Cornell. So, the research group that I joined, Packard's group, said, "Well, we've got to get involved in that." There, the technical difficulty is not this imaging, it's how to get down to temperatures of 1/1,000th of a kelvin as opposed to 2 kelvin. So, the refrigeration aspect of it was vastly harder, so that was a big technological challenge. We spent our first two years of research was getting what's called a nuclear demagnetization refrigerator to reach the required temperature range, and stay there for a little while. [laugh] That's hard.

ZIERLER: How'd you do it?

EISENSTEIN: It's a series of steps. Do you know what nuclear demagnetization is?

ZIERLER: No.

EISENSTEIN: The basic idea is that if you have a system, magnetic system of spins, and they're at some temperature in a magnetic field, some fraction of them are pointed up, some fraction are pointed down, and the difference between the two populations is determined by the magnetic field. The stronger the magnetic field is, the more of them point up because they get magnetized. So, if you do this, and you have it at some magnetic field and some temperature, some starting point, let's say—oh, I don't know—50 millikelvin at 10 tesla in copper, some tiny fraction, excess fraction of the nuclear spins in copper are pointing up versus down. If no magnetic field, they'd be fifty-fifty, and there's no magnetization at all. Now, you disconnect this piece of copper from the universe, in the sense of you won't let it exchange heat by isolating it thermally. What does that mean? Its entropy is now going to remain constant, and you slowly turn down the magnetic field. As you slowly turn down the magnetic field, the entropy has to remain constant. The only way that can happen is if the temperature goes down. The temperature must go down as the magnetic fields go down. In fact, B over T will—I mean, ideally—will remain constant. You turn it down and down and down, and the temperature goes down, down, down, until the inevitable imperfections of this technique take over, of which there are many, and you reach some very low temperature. This was not something Packard invented. This was invented a long time ago—at Berkeley, no less. So, we would start at a temperature of about 15 millikelvin, which is something you get with something called dilution refrigeration, which is another technology we could talk about if you're really interested. That's conventional—it's not conventional. That's the wrong word. That works like your refrigerator works at home but with not Freon, with something else, which we could talk about. So, it'll continuously go down to some low temperature where it can't get any lower because it's balanced by residual heat coming in.

ZIERLER: Let's talk about it. What is that something else?

EISENSTEIN: It's actually—it turns out that—so dilution refrig…so, let me finish the—I'll get back to that in a second. That would be the machine that would get us to the starting point. We would have the magnet on at 10 tesla, let the dilution refrigerator work all night to try to get the piece of copper to like 15 millikelvin or 20 millikelvin, and then we would turn off what's called the heat switch, which was the thing that kept the copper isolated or not isolated from the dilution refrigerator—and we can talk about that too, but that's a detail. Then we would slowly over a period of hours turn the magnetic field off because the magnetic field changing in time creates its own source of heat, and you don't want that. So, you do it very slowly, and the temperature would go down until it reached a point where other effects dominated, and it was as cold as you were going to get. We could get to—on a good day—to 500 microkelvin that way. This is a piece of copper that weighs 5 pounds, and it's all at 500 microkelvin. It's pretty incredible. Then that piece of copper had in it a sample cell containing helium-3, which was our experimental subject of interest. So, the helium-3 would be in communication with the copper, and would also get cold, and then we would perform experiments on the helium-3 very carefully. So, back to dilution refrigeration, so you know that the simplest refrigeration you can think of is sweat evaporating off your body when you're out running, and it gets cold, or you blow air over your sweaty arm, and it feels chilly because evaporation causes cooling. It takes energy to kick an atom or a molecule out of molecule water into the vapor phase. In dilution refrigeration, you don't have any liquid like water to use because they're all frozen, so you need something else. The only liquids available are the helium liquids. They're the only liquids on Earth in the universe that can be maintained in a liquid state down to absolute zero. They will never freeze because quantum mechanics—quantum mechanical zero-point motion is so vigorous that they just can never settle down, unless you pressurize them. But let's not worry about that. You can solidify them, but you have to put on a lot of pressure.

So, with helium-4, if you did that, it wouldn't be very interesting, or pure helium-3, it wouldn't be very interesting because vapor pressure, as you pump away the vapor, try to make it cold, just like the sweat on your arm, you're pumping away the vapor, it does get cold but the vapor pressure drops exponentially. But it gets down to some incredibly small value, and the residual effects become dominant, and you can't get any colder. If you take a bucket of helium-4, and you try to cool it by evaporation, you get to maybe .8 kelvin if you go to enormous effort. With helium-3, you do the same thing, get to .3 kelvin, that's it, because of this exponential dependence. Oh, but somebody discovered in the 1950s or 1960s that a mixture of helium-3 in helium-4 did something very strange. At low temperatures, a 6% mixture of helium-3 and helium-4 remains insoluble, and so the helium-3 percentage, as you go down to low temperatures, remain 6%. So, it's like having a vapor pressure of helium. Think of the partial pressure of helium-3 inside this mixture. It can't be reduced below 6%. So, you make this mixture of helium-4 with 6% helium-3 in it, and on top of it, a layer of helium-3, and think of the pure helium-3 as the water on your arm, and the helium-4 with the 6% helium-3 as the vapor of water. The helium-4's only function is to hold up the whole thing so it doesn't collapse.

Now, try to evaporate a helium-3 atom across that interface, and you keep doing that over and over and over again, and it never—the percentage never goes down. So, you keep gaining. It's a tiny, little bit. The latent heat is ridiculously small, but it's not zero, and you just keep doing that. It's a closed circuit. It's going around and around and around. But you keep doing this, and energy has to keep flowing in. So, in principle, a dilution refrigerator will cool down to absolute zero, but residual effects always come in. Commercial dilution refrigerators cool to about 5 or 6 millikelvin, and then they kind of run out of gas. But that's something—5 or 6 millikelvin is vastly colder than you could get by simply pumping on helium-4 or helium-3 alone. This was discovered in the '50s or the '60s, and gave rise to the invention of dilution refrigerators. As a graduate student, we had one of the earliest commercial versions of this, built by a company in San Diego, and it would get to 12 millikelvin. That's what provided the engine to allow us to start the demagnetization cycle to then go to still lower temperatures with this 50—500 microkelvin. That's a long story.

ZIERLER: Yeah.

EISENSTEIN: It's a complicated business. Now, it's turnkey. Now, kids come into the lab, and the professor has spent $700,000 on a machine that you simply press a button, and go away for 36 or 40 hours, and come back, and it's at 15 millikelvin. My generation scoffs at that. It was so hard to get them to work, but it's not anymore. But God save the student if the thing breaks.

ZIERLER: [laugh]

EISENSTEIN: [laugh]

ZIERLER: So, fundamentally, it's like freon in our home refrigerators?

EISENSTEIN: Oh, yeah. Yeah, yeah. It's a phase transformation. It's going from pure helium-3 into this mixture, which those are the two phases: the so-called concentrated phase, which is all helium-3, and the so-called dilute phase, which is this pretty high percentage—6% is a big number—of helium-3 atoms floating around in helium-4. That's the gas, the helium-3 concentrated, it's the liquid. Draw the atoms across that interface, you're guaranteed to get a latent heat out of that, and that's the refrigeration mechanism.

ZIERLER: Jim, where in this narrative do you transfer from lab tech to scientist? Where are you slotting in for your own thesis research?

EISENSTEIN: That's a good question. It was really easy. The blackboard was always covered with 500 things that were broken, and had to be fixed, and you check them off and check them off and check them off. You could spend your life doing that if you weren't careful. So, I was always on the lookout, and I think more so than my thesis advisor and more so than my other fellow graduate students. Let's do something, guys. Let's measure something, I don't care what it is. Let's do something. We've got this machine, and maybe it doesn't work quite as good as you'd like it to work, but it works a little bit. Let's do something. You have to think about what—so, you do have to have your ear to the ground, and you have to be reading the literature. What are the problems you might be able to do with this machine that's almost good enough to do what you'd really want to do? So, I did that, and came up with some experiments early—not early—after two years of battling cryogenics to do an experiment. So, that's how it got going.

My first experiment was not involving superfluid helium-3. We hadn't reached that temperature yet. But it was just above the superconducting tem…superfluid temperature, and it was a pretty interesting experiment, it turned out. I don't know. If you don't pay attention to what's going on, you will—you'll get stuck on that blackboard, and some kids do. Some students do. I used to tell my graduate students, the hardest thing in the—I learned this from Venky more than anybody else. The hardest thing in the world is to figure out what experiments are worth doing; not experiment—what experiment can I do. There's a big distinction there, and it's easy to get stuck thinking of experiments and doing experiments that you're capable of but maybe aren't really the most important things—the best way you could spend your time.

ZIERLER: So, of all the things to measure, how did you figure out what to measure? What were the questions to ask?

EISENSTEIN: Well, in this case, as a graduate student when things were getting going, I was very interested—I have a theoretical bent, even though I'm not a theorist. I was very interested in the fact that helium-3 when it forms a liquid, it's a liquid of fermions. A Fermi liquid, like the electrons in a metal, they have certain properties, and they're—say, for example, you take a piece of copper, and you ask, what is its electronic heat capacity? Just a straightforward thing. It's proportional to temperature, the heat capacity. But why is that? It's proportional to temperature because electrons are fermions, and fermions fill up a Fermi sea, and there's only a small fraction of them near the surface of the Fermi sea that can do anything. Because that small fraction is there, the heat capacity must go to zero as the temperature goes down. It turns out it goes to zero linearly in temperature. It's a fundamental property of a collection of fermions. We had this system, which was not electrons, so they weren't charged. They were neutral. I'm not sure but it could be this was the only neutral fermion system that people were studying. I'm not sure there was another one. I'd have to go and look. So, a charge-neutral Fermi liquid, I said, "Let's measure some of those Fermi liquid properties, and see if they work like heat capacity."

Some people were working on heat capacity, for sure, at the Cornell group, for example. I said, well, we—I was doing what are called hydrodynamic experiments on the liquid. What does that mean? Make the liquid flow through a pipe, and see what happens, right. What can we do? Let's look at the viscosity of helium-3. Here's an interesting thing. You know what viscosity is, obviously, so honey is very viscous. Water is not very viscous. Alcohol's even less viscous. Water, from personal experience, you know sort of what water's like. You know what olive oil is like too. It's more viscous. Helium-3, if you get it to 1 millikelvin, right before it becomes a superfluid, it's like olive oil. As you go up in temperature, it becomes more and more like water. It turns out that temperature dependence is not linear, it's quadratic—so said the theory. I said we can measure that with my—with the apparatus that I was working on. We can measure that, and we did. We measured it, and we published a paper on the viscosity of helium-3, and deviations from the simple law that you read about in undergraduate physics books. It wasn't super important but it was important to me. It was an experiment we were able to do successfully on this system that wasn't quite yet good enough to do the superfluid experiments we were going to do, and which we eventually did do. I don't know if that explains but that's—

ZIERLER: Yeah.

EISENSTEIN: Helium-3 is a strange fluid. Number one, it never freezes unless you pressurize it enormously. You think about that. It doesn't ever freeze, no matter how cold you get it. It has these properties related to the—when it gets right down to it, it's related to the fact that three is an odd number, and four is an even number. It's a Fermi—it's a system of fermions, and so it has peculiar properties that are analogous to the properties of electrons in metals, except that it's not charged. So, it's a very interesting system. I said why can't we do some experiments on what we call the normal phase of the material above the superconducting transition temperature, superfluid transition temperature, so above 1 millikelvin? So, I did an experiment. The title of my thesis is Flow Properties of Liquid Helium-3 Below 5 Millidegrees. That was what I was advised to make the title by my thesis advisor, except, well, we may never get to the superfluid phase, so hedge your bets a little bit, and say you're doing experiments at higher temperatures also. That was actually good advice because the first experiment was on the normal fluid, this viscosity business.

ZIERLER: How did you know you had enough to defend?

EISENSTEIN: I had plenty. I had more than enough, and I wanted to get the hell out of graduate school. We haven't talked about whether that was a pleasant time or not. It was so hard. I worked harder than I've ever worked in my life as a graduate student. I had a wife and two children toward the end of graduate school, so it was—

ZIERLER: Time to get a job?

EISENSTEIN: It was time to get a job, and I had plenty of results. There was no shortage of results. The viscosity was just the first one. But then we did get into the superfluid phase. We did a bunch of experiments there too. Again, hydrodynam…my corner of the subject was hydrodynamics because when you say superfluid, what does that conjure up? It conjures up the idea of a fluid that has no viscosity, and does magical things like helium-4 did. Would helium-3 do the same things? As the years have gone by, we realize, yeah, it does. We didn't know that at first. We didn't know that it would, and so you do experiments where you literally move the fluid physically. So, that's what I did my thesis on.

ZIERLER: What were some of the big conclusions with all of these findings?

EISENSTEIN: Well, the first one, I guess, was that helium-3, you had to be extremely careful in order to exhibit superfluid properties. In a hydrodynamic experiment, you had to make sure that other processes were not eliminating this so-called zero viscosity, this so-called superfluid behavior. I ran headfirst into those problems, and so we got a lot of interesting results on the fact that it didn't flow like a superfluid. It flew—it flowed much more with much less viscosity than it did right above 1 millikelvin where it was like olive oil, as I was describing to you. So, it went—but it wasn't completely free of dissipation. We struggled, actually, for a long time until even after I left my PhD to figure out why it wasn't doing what we had naively thought it should do. That got figured out eventually, but it wasn't obvious at the time. So, there was that.

My first paper dealt with the fact that if you take a superfluid, even helium-4, and try to make it flow too quickly, it'll break down. If you make—there's something called a critical velocity or a critical current. Same thing with the superconductor, right? You drive too much current through the wire, and it won't be a superconductor anymore, often with dramatic consequences. So, there are things called critical currents, and my first paper actually was not on viscosity because it took a long time to get that quantitatively in good shape, and a lot of theoretical discussions, by the way. We discovered critical currents for the first time in helium-3, which had not been observed before, so that was exciting. That was our first Physical Review Letter. So, that was one. This dissipation, this unexpected dissipation was another one. I studied the magnetic properties. Helium-3 is a very complicated system. Helium-4 is simple by comparison.

Let's see. So, you know about superconductivity. We had this idea that they're pairs of electrons. This is a real oversimplification, this idea. So, they're going around. You can ask what's the orbital angular momentum that they have? In a normal superconductor like aluminum or lead, that answer is zero. They're in what's called an S-wave state. There's no net angular momentum of the pairing. They're always—somehow it all cancels out. It's an S-wave. Just like the lowest energy orbital of an electron going around the nucleus, the hydrogen nucleus, it's an S-wave. It's a 1s state, with no net orbital angular momentum. Helium-4 is kind of like that in a way. Helium-3, it turns out, is not like that. It was the first known example of what's called a P-wave superfluid. In other words, the pairs actually orbit in such a way that they really do have an angular momentum. There's a 1s state of hydrogen. Then there's the 2p state. If you want to go to the 2p state, you have to have net angular momentum of the electron going around. In an ordinary superconductor, that doesn't happen. But in helium-3, it turned out all—and people recognized this almost right away that this was not an S-wave because it had weird anisotropic properties, weird magnetic properties that turned out to be because the pairs were in orbital angular momentum 1.

So, this was a huge deal in this little corner of physics that we discovered—not "we" but the field had discovered the first P-wave superfluid or superconductor. There are now thoughts that P-wave superconductors appear in other physical systems—none of them as well-established as helium-3. The beauty of liquid helium, one of its real beauties is that there are no impurities. You get yourself a bucket of liquid helium, you take it down to low temperatures, all the impurities stick on the walls, and it's utterly pure. The only impurity in helium-4 is helium-3.

ZIERLER: [laugh]

EISENSTEIN: No, it's true, absolutely true. So, everybody's sample is the same. You realize how important that is?

ZIERLER: Yeah.

EISENSTEIN: Because in condensed matter physics, it's a disaster. In the early days of high-temperature superconductivity, there were a million different results because people were making up a million different compounds in totally uncontrolled ways. There were impurities here, and dislocations there, and all that stuff that comes with honest, real, solid-state materials. None of it's present in helium.

ZIERLER: Helium-3 is the perfect control?

EISENSTEIN: Perfect control. Perfect control, and so there's a tremendous simplification because of that, and the subtlety of the inherent physics is a lot easier to figure out. Even though it's quite complex, it's—you're never worried that, well, maybe there's potassium in my sample. [laugh] But in doing an experiment in solid-state physics, there's always some worry—and this is true of the quantum Hall effect—that, well, maybe it's disorder. What is disorder? It's this stuff you don't know about that's going on inside your material—dislocations, impurities—stuff which you can't control. The crystal growers are never perfect. Helium-4 gets around all of that. That's the beauty of the field. Helium-3 and helium-4 both get around that completely.

ZIERLER: Jim, were there labs elsewhere that were sort of in a race, given how exciting all of these findings were?

EISENSTEIN: Oh, yeah. Oh, yeah. The premier place in the country, in the world, I would say—yeah, I think it's true—in the world was Cornell, which was where the discovery was made by Doug Osheroff and his thesis advisor Dave Lee, and Bob Richardson. But there were groups all over the world—Finland, lots in England, lots in Germany, lots in Japan; lots in a very narrow field. You look up the citations of somebody famous in the field of helium, and they're really famous. They're brilliant physicists…but there aren't very many citations. Why? The field is tiny, that's why. That's the only reason. Then you look up the citations of somebody who's kind of a middle-of-the-road physicist. They got a gazillion citations in a field that's huge. So, it's a very narrow field in that way, and it struggles. It's always struggled against the NSF and the funding agencies. They tolerate helium-3, helium but it's small potatoes.

ZIERLER: Who was on your thesis committee?

EISENSTEIN: Let's see. Can I remember? Do you know that at Berkeley, there's no thesis defense, or there wasn't when I was there?

ZIERLER: No oral defense?

EISENSTEIN: No.

ZIERLER: Huh.

EISENSTEIN: No, you just hand in your thesis. I don't know if that's still true. But it's well-known that it was true then. There was a fellow named Norman Phillips in the Chemistry Department who was extremely well-known for studying the thermodynamic properties of helium at low temperatures, so he was a good person to have on the committee. There was a guy named—a physicist named Alan Portis, who was on my committee. Then there was an NMR guy from, again, chemistry. No, no, there was a mathematician. I invited a mathematician to be on my committee because I fancied myself somehow more mathematically sophisticated than others, which was really arrogant and stupid. But, anyway, he was on my committee. They all looked the thesis over, and nobody had any—it was actually very disappointing in a sense that they really didn't have anything to say. Alan—God bless Alan Portis. He's long since deceased. But his only comment was, "It's a very nice thesis but you should change all your figures from landscape to portrait." OK.

ZIERLER: [laugh]

EISENSTEIN: Back then, that was no small deal—

ZIERLER: Yeah.

EISENSTEIN: —because we had to go to an artist in downtown Berkeley, and he had to redo all the figures. It was a big deal, very expensive, back then. Norman Phillips read my thesis, and there was one offhand comment in it that I made about an offset in a particular amplifier that was influencing our ability to get an absolute value for the temperature. He said, "What's this offset?" So, I need to talk about that. The mathematician, I don't think he had any comments at all. He was also on my qualifying committee, and he asked me something about simple harmonic oscillators, which I was able to answer [laugh], fortunately for me. [laugh] He was a nice guy.

ZIERLER: Jim, what did you want to do after you defended? What opportunities were available?

EISENSTEIN: Get the hell out of graduate school.

ZIERLER: Yeah.

EISENSTEIN: I was utterly exhausted, and my wife had had enough. I had, I think, a dream that a lot of young people have. I had a wonderful education at Oberlin. I had a very romantic view of it, you know, an immature but very romantic view of it. I said what I really want to do is teach and do a small amount of research at a fancy college. So, I didn't even apply for any postdocs. I just applied for academic positions at colleges, and I got—I applied to places like Swarthmore and, again, some safety schools. Williams College got very interested in me, and I ended up going to Williams College pretty much right after graduate school. I became an assistant professor the very next fall, a few months after leaving Berkeley, and got thrown into teaching full-time.

ZIERLER: So, Bell Labs is not on your radar at this point?

EISENSTEIN: No, I was convinced I was done with research. I was exhausted.

ZIERLER: Yeah.

EISENSTEIN: I was really, really exhausted. My wife…it's no exaggeration that during—when I got into the research group after the couple of years as a TA, the four years I spent working in Packard's research group, I took off Sunday mornings, and that was it, Sunday mornings. That's ridiculous, right. So, I worked very, very hard, every night back to the lab from 8 o'clock to 11 o'clock, and so I was exhausted by that. I thought, erroneously, that what I wanted to do was teach ult… you know, dominantly but carry on the kind of research that Joe Snider had done at Oberlin, at that level, because I so admired what he had done there. I set up a research effort at Williams College, even got an NSF grant—they have grants for little colleges—and very quickly realized that I'd made a mistake.

ZIERLER: Once you had taken a deep breath?

Williams College and Small Town Life

EISENSTEIN: Yeah. Yeah, it wasn't that—you know, Williams, I mean, they had great students, a very fancy pants college with rich kids and other resources, and they treated me very well. I can't argue with the way they treated me. Teaching was—I had no idea how hard it was to teach. Even though I had done a little fiddling around as a TA, it was a joke compared to when I had to go in and teach quantum mechanics three days a week. I just couldn't believe how hard it was. I had to relearn everything. I tried to carry on some research at Williams College. We had little babies, and it snowed like no tomorrow the first couple of winters we were there, and my wife was just having a really hard time of it. I began looking for escape hatches within six months of arriving.

ZIERLER: Oh, wow.

EISENSTEIN: I mean, there—those places—I don't know. I don't want to generalize. But I know it's true of Williams. They seemed arrogant there. The provost had a dinner party for the incoming new faculty, of which there were quite a number. They went to a dinner party where upon he announced to us that one in six of us would get tenure, which is, you know, give me a break. This is—we were excited. We were launching off into a new career, and you're telling us that five out of six times, we're going to fail. I thought that's just terrible. So, I was upset by that. I think, in the end, I wouldn't have failed because I turned out to be a very good teacher, and I got a research grant, which was like a miracle there—a big one too. But I said this is not for me. I wanted—I realized I was not exhausted with the idea of doing research. I was exhausted with having done it to the extreme that I had done it as a graduate student. So, I started looking for escape hatches immediately.

ZIERLER: Academic and industry?

EISENSTEIN: I didn't look in industry. I only looked academically. I interviewed at a few places—they interviewed me at Purdue; they interviewed me at Hopkins; University of Delaware—over a period of two years. I'll never forget the interview at Hopkins. A bunch of astrophysicists were talking to me in one of the many interviews I had there. They just said, "Why don't you just go be a postdoc somewhere?" There I was, a job applicant for them. Their Physics Department had invited me for an assistant professor position. They didn't even pay my bill in the end, the Hopkins guys. [laugh] University—no, BU, Boston University. But I didn't get any of them, until finally I got a job offer at the University of Delaware. The chairman of the department was a guy named Henry Glyde, and he was very nice to me, and he had a helium background, and we got along famously, and they made me a job offer. The University of Delaware is a good enough place but, from a research point of view, this was not going to be nirvana. Then I got rescued. I got rescued because of Venky. The reason I got rescued because of Venky was because of a man named Mike Sturge, who was a very well-known Bell Labs physicist, a British fellow, famous in the field of excitons, who had decided he'd had enough of Bell Labs, and wanted to go teach at a small college. Thought he'd try it out for a year on sabbatical, which you don't get at Bell Labs. But, somehow, he finagled one. He went to Williams College. I'll never forget the day he came into me. He said, "These students, they don't know what reciprocal space is." [laugh] I had to keep from laughing. I said, "Come on, Mike [laugh], I don't even hardly know what reciprocal space is."

ZIERLER: [laugh]

EISENSTEIN: "They don't know." Anyway, he had a good contact with Bell Labs, obviously. He came to me one day, and he said, "Oh, there's this guy, Venky [Narayanamurti]. Venky's looking for a new postdoc," because I talked to Mike a little bit. He was very nice to me, and he knew that I was sort of on the job market. I didn't hide it from anybody. They all knew it. "Why don't you give this guy Venky a call?" I called him up. Venky saved my life, he really did.

ZIERLER: Had you known him before?

EISENSTEIN: No. No, never even heard of him. I went down to Bell Labs, and I said—I went to my interview there, and I said to myself, "If I don't get this job, I'm going to shoot myself." I said, "This is where I want to work." I went there, and I saw—I don't know if you've ever—well, you're too young. But back in the day, a quarter of a mile-long corridor, and there's a helium or a liquid nitrogen dewar outside of every door. I said, "This is it. This is condensed matter physics at a level that I didn't dream existed." Venky took a risk with me. I was—one more year, and it would've been over because I was at the end of three years at Williams College. Williams gave me—and they did it with all assistant professors because of the five over six rule. They were going to kick them out anyway. So, they gave them a year after three years to go out and look for another job [laugh], like a sabbatical, a mini sabbatical. They paid our salary, or some fraction of it. So, I had a good opportunity to go down there for this postdoc that Venky then offered me.

ZIERLER: What was Venky doing at that point?

EISENSTEIN: He was the director of something called the Semiconductor Electronics Research Laboratory. The Research Division, the really fundamental Research Division was divided into three things called laboratories. There was one called chemical physics, even though it was physics. There was one called semiconductor electronics, which was physics. There was one called physics, which was physics.

ZIERLER: [laugh]

EISENSTEIN: Each one of them had about 80 to 100 PhDs in it. Imagine that. It's like a physics department with 300 PhDs all doing some version of condensed matter physics. It was like, you know, this is incredible. This doesn't exist anywhere else in the universe. Venky's research…I mean, he was a manager by that point. But he had a long-standing interest in physics of phonons and solids, and physics of superconductors, and, believe it or not, interesting experiments on helium-4, which he did with Bob Dynes, another famous—who was also a director at the same time. Venky and Bob Dynes were good friends, and they interviewed me together, and—I don't know—they talked with Doug Osheroff, who was able to tell them that the work I had done on superfluid helium-3—because Doug was the discoverer of it—was not junk; that I'd done a good job. Venky took a risk on me. Really, if it'd been another year, I would've been past the point of no return to the active research world.

ZIERLER: The risk was, what, that you had demonstrated that research was too exhausting for you at Berkeley?

EISENSTEIN: No, I think it's just that I was getting too far away from it, and so I wasn't going to be as knowledgeable; that I'd made this big decision, and I'd gone off to a non-research thing. Your stock goes down with time.

ZIERLER: How were—how did you know that this would not be Berkeley redux; that you wouldn't get exhausted all over again?

EISENSTEIN: I didn't. I didn't know that. I had the advantage though that this was a one-year—initially—a one-year appointment with a promise that Williams would take me back--not necessarily tenure me--but take me back for the second three years. Williams, by this point, really wanted me to stay. I believe they would've tenured me--I don't know for sure--but I think they would've tenured me, had I stayed there. So, I had an escape valve if it didn't—if I ended up finding out it was just as bad as Berkeley. But, again, God bless Richard Packard. He gave me tremendous skills. But I didn't like him very much, and he didn't like me either. We had a tough time. So, part of my feelings about graduate school were heavily influenced by a difficult interpersonal relationship with my thesis advisor. So, if you divide that out, it's unclear where you land.

ZIERLER: Yeah.

EISENSTEIN: But, anyway, I got into Bell Labs, and there was no turning back at that point. I started working

ZIERLER: This is before Judge [Harold H.] Greene, no inkling of the breakup, nothing like that at this point?

EISENSTEIN: Judge Greene was out there. I remember hearing about him pretty much very soon. But nobody—but the final decision hadn't come down. What's the phrase? Party like there's no tomorrow. That's sort of what people were doing at Bell Labs. I like to say it's like a big ship that has a very small hole in it. It's going to sink. It'll take a long time. That's what happened. So, I got there, and Venky was my idea of the best possible postdoc advisor. He gave me all the freedom I could possibly want, constantly encouraged me, came in every day, told me how great I was and how tired he was. It was always fun, always. He's a brilliant manager, like on another level kind of. He's the kind of person who brings out the best in people with some—in some effortless ability that I don't really know where it comes from. But he would come into the lab at the end of the day when he'd be tired because he'd have all this administrative crap to do all day, and he'd say—he always said the same thing. He'd walk in the lab, a very tiny, little lab. It was very crowded, all the equipment all over the place. He would look at me and say, "Jim, what's the good word?" That's what he would say. "What's the good word?" And what he meant is he wanted to sit down, and talk about what I did that day for 20 minutes or 15 minutes. It was great.

ZIERLER: Did you move the family down for that year, or they—

EISENSTEIN: Oh, yeah.

ZIERLER: —stayed up in Massachusetts?

EISENSTEIN: Oh, yeah. Oh, yeah, because we had our fingers crossed, this is going to work out. Yeah, we moved the whole family, and it was a big deal, obviously, to do that. Then on top of Venky—maybe we'll talk about this more later—I met Horst Störmer.

ZIERLER: Yeah, yeah.

EISENSTEIN: He was another example, in a different way, another guy who knew how to bring out the best in people. Those two people in particular, I would not be where I am today without them, no way.

Bell Labs and the Quantum Hall Effect

ZIERLER: What was the initial project? What were you doing to start out at Bell?

EISENSTEIN: That's a funny question, though probably I didn't like it. Venky and Bob Dynes had this interest in something which at the time was very sort of avant-garde at the time. It's called spin glasses. Spin glasses are like glasses. What do you think of when you think of glass? (A) It's an insulator, and then (b) you think about some dynamic crystal and structure, and something which, if it moves at all, moves extremely slowly [laugh] on geologic timescales. The spins in certain metals like copper with the small amount of manganese thrown in, the manganese ions are magnetic, and they form a disordered array of magnets, and has certain properties which are glassy, long time constants. God knows why people were so interested in them, but they were, and I have not followed this field at all. But Venky said to me, "Why don't you go measure the heat capacity of spin glass because it should have the following—the theories say it should do this and this?" I don't even remember what it was. For this, I worked mostly with Bob Dynes, actually. I got there in July of 1983, and I worked on it for a while. I kept hearing noises about this Horst Störmer guy, and this quantum Hall effect. You have to be brain dead not to think the quantum Hall effect is interesting.

ZIERLER: Yeah.

EISENSTEIN: Glasses, you have to be very sophisticated to think they're not boring. They're very—they're difficult, really difficult. So, I was working on this, and did some experiments. I was watching somebody else, a previous postdoc of Venky's, and somebody else trying—and Horst trying to measure the magnetic moment of a quantum Hall effect system. I remember I came in one day, and I said, "Well, what about doing it this way?" They said, "That'll never work." I went to Venky, and I said, "I got this idea. Number one, I don't like working on spin glasses. It's boring." Venky said, "OK." That's not a small thing.

ZIERLER: Yeah.

EISENSTEIN: He said, "OK. What have you got?" I'm up in the director's office. Eileen Marciniak lets me in the door because I'm Jim, and Venky's postdoc. Otherwise, you don't get in the door. He said, "Well, tell me about what you want to do." I describe this experiment, and there's the magnetization of the quantum Hall system. He said, "OK, go try it."

ZIERLER: [laugh]

EISENSTEIN: That was it. He said, "That's interesting. Go try it." Lo and behold, it worked, lo and behold, and it was me. I made it with my idea, and it wasn't like it was—other people could've thought of the concept, in fact, and probably did. But most people thought you'll never get it to work well enough. There aren't enough electrons in the quantum Hall system to ever have a signal you can measure. Having worked with this guy Packard doing incredibly hard experiments with signals that you could barely measure, I wasn't so afraid of this, and said I'm going to try it. Lo and behold, it worked, and that was it.

ZIERLER: What worked, exactly? What was the question? What was the result?

EISENSTEIN: You'll know of this. You learned about the Cavendish experiment for measuring gravity.

ZIERLER: Yeah.

EISENSTEIN: How did it work? It was some big balls on a torsional pendulum with a tiny, little fiber—big, heavy things. The fiber's sitting there, and the balls are there, and it's got a little mirror on it, and they're shining light on the mirror, and the reflection is on the wall. OK. Then they bring another ball out. Very carefully, without vibrating it, they bring another big, heavy ball next to one of them. There's some gravitational force, and the thing twists a little bit. It's extremely small. The fiber has to be really thin, and the light ray has to go a long distance and had multiple reflections so you can detect this tiny torsional motion. Cavendish did that, and it worked. I said to myself—I wasn't thinking of Cavendish—but I said, "Why don't we try to measure the torque on a quantum Hall sample that's mounted on a very thin fiber? That torque will twist the fiber, and we'll put some capacitor plates on the thing, and those"—because I did capacitance measurements as a graduate student, high-precision capacitance measurements, I knew how to do them. That capacitance will change by a part in a million and that's not hard to measure with electronics. They all said, "It'll never work." Even Horst said it'll never work, and Horst is a genius experimentally. He said it won't work. It worked. It's worked. The whole thing moved. As a function of magnetic field, we could see it oscillate, which is a famous effect called the de Haas-van Alphen effect, which is known from solids. It's very important.

It turns out it's a diagnostic tool for learning about the Fermi surface of solids first measured, I think, by a guy named Shoenberg. Maybe Shoenberg, I don't know. So, as a function of magnetic field, things oscillate, and they oscillate because of the energy levels that the magnetic field induces either in the metal or, in this case, a two-dimensional electron gas. You go through this series of quantum states, and so the thing oscillates. The very first time I put the sample in and turned up the magnetic field, it oscillated. Venky came in the door at about the same moment, and he looked at it, and he goes, "I can't believe it." This is in November, after having been there, and fiddling around with this stupid spin glass for a couple of months. I built this thing called a magnetometer, a torsional magnetometer, which is not a—that's not like a big invention. But it's the—the thing was that I was the only person who said—I was ignorant enough to say, "Well, let's give it a try. Maybe it'll work. Everybody said it won't work." And it worked. Venky walked in the door, and he looked at it, and he said, "I can't believe it. You're a success." I remember his words. He said, "You're a success already." Boy, that did me some good. [laugh] That really did me some good. That was the kind of guy Venky was. He just—he didn't stint on giving credit where credit was due. He must've sensed that interviewing me.

ZIERLER: Absolutely.

EISENSTEIN: He's a special guy, he really is. His wife is too. I don't know if you ever met her. But his wife taught me how to cook. That's a whole other story.

ZIERLER: [laugh] Jim, what did you do with the results? Were you on the conference circuit? Were you writing papers?

EISENSTEIN: Immediately, I guess, let's see, how did it go? Yes, we wrote a paper right away. Truth be told, the previous postdoc had tried a different way of doing it, and with Horst. They had some—it wasn't that we saw the first such oscillations, but they were pretty terrible, the quality of them. They had sort of already published something, and we had to make sure that we had something sufficiently different that it was worthy of a Physical Review Letter. To do that—and the technique was great. I went out, and I gave talks about it at the March Meeting, and so forth. Got a lot of good attention from people.

But the Phys. Rev. Letter took another year to get. The reason was the thing we wanted to do beyond the initial measurements was try to measure—so, these two-dimensional electron systems, you can get them in a single layer in a crystal, or you can build lots of layers up, and then you can take lots of samples, and add them all together [laugh], and put them on the magnetometer, whatever it is. That's what Horst and this previous student, previous postdoc had done. They'd taken some multilayer systems, and stacked up a lot of pieces, and gotten a very poor signal, but a signal. They definitely saw it, saw the effect. So, we said the only way we're going to get a PRL out of this is you got to do a single layer because single-layer samples are much higher quality than the multilayer samples. So, does your technique have the signal-to-noise needed to see a single layer? The answer was, after a year and a half, yes, we can do it, and we did do that. So, that's what got the final—actually the really important publication that came out of it. There were some other ancillary things but that was the PRL that we got for it. I did other things along the way because it took a while to get a good sample. When you get down into the weeds, everything takes a long time. Maybe I got lucky. The first sample, this multilayer sample just worked like crazy, and I had signal-to-noise of 100 to 1—100 to 1. This previous experiment that they had done with Horst, they had a signal-to-noise ratio of one, so it was hard to get the signal out. I had—you can just come, and any idiot can look at the data and say, "Yeah, it works." [laugh]

ZIERLER: Jim, to go back to the interplay between theory and experiment, at this time in at Bell Labs, were you talking to theorists? Were they interested in this work?

EISENSTEIN: Let me think if I can remember this. [pause] I don't remember talking—this is—I'd only been there for three months or four months when we got the first results, and I didn't even go down the theory corridor. You're afraid to. Phil Anderson was down there, and I was just this young squirt. I didn't know anything. So, I didn't talk to theorists then. Two people changed that. Both of them were not at Bell Labs. One of them was Bert. Bert had been at Bell Labs, as you now know. He would come down as a consultant or whatever, and he'd make the daily rounds, and talk to different—he came in. Bert is one of the most amazing theorists I know because he'll come in, and you'll be talking to him, and he'll ask you an experimental question that you can't answer. Even though the guy couldn't do an experiment but he knows the right question to ask, always. So, he got very interested. He was interested. He didn't work on it, but he was very stimulating to me, and I felt—and I was overawed at this guy because I'd heard about him by this point, and knew that this guy was a very famous theorist. So, that was the first one. I think he was first. But then there was another guy who was very important to me, a fellow named Sankar Das Sarma, who is a professor now, and has been for many years, at the University of Maryland. He's a theorist. One of the things I like—he's— (a) extremely skilled, and (b) willing to look at experiments, and actually calculate something. That's a problem with a lot of theorists, and it's understandable because experiments are dirty, and there's effects going on, and they don't know how to model. They can work at an idealized environment very easily. But when it starts to be, "Oh, you've got impurities? I don't know what to do," it gets much harder for them. Sankar was willing to—maybe not always with the exact right approach—but he was willing to face up to these things, and make an honest attempt to calculate something—and he did so for my experiments. That was important to me. He was young. He's the same age as I am. He's even a little younger than me, maybe a year or two younger than me.

Sankar has been interested—was interested in my experiments all along, for many, many years. He can calculate stuff.

ZIERLER: Jim, while all of this was happening, the proverbial hole in the ship, did you feel it was getting bigger; that Bell Labs was in trouble?

EISENSTEIN: Not for a while. Not for a while because I didn't know anything about the company, really. I just knew they were the phone company, and we—I never had to ask could I buy something?

ZIERLER: Yeah.

EISENSTEIN: They say, "Of course, go buy it." I remember Venky once gave me a little trouble for about 20 seconds.

ZIERLER: [laugh]

EISENSTEIN: I wanted to buy some $20,000 piece of electronics, and he said, "Do you really need that?" I said, "Yes." He said, "OK." [laugh] It was about that long. So, the Judge Greene decision came down in '84, and, basically, everybody just kept on partying, at least in the research area. It's as though this doesn't really matter, and they created this Frankenstein thing called Bellcore. I don't know if you know about that history a little bit.

ZIERLER: Sure.

EISENSTEIN: I guess Venky certainly told you about this probably. Maybe you know anyway. Some 10% of the research staff left as part of Judge Greene's decision, just to create this other laboratory connected with the local phone companies. The local phone companies didn't even want it but it was required by the settlement. So, those people kind of left. But the labs just kept on going, and it kept on going and going and going and going and going. I kept going to conferences. Every once in a while, somebody would make noise about doing something that the company needed. But they never made very much noise about it. Besides, there were always people doing stuff that the company needed. So, it just didn't sink in until the early '90s, really. By '96 or '95, AT&T decided to spin off the labs, separate them from AT&T. That's when everybody—I mean, that's when you had to know that the party was coming to an end.

They created this company called Lucent Technologies. I remember very well I had already decided to leave Bell Labs. The common pathway through Bell Labs was to go there and stay there for a fragment of your career, and then move on to an academic position. Not many people stayed so that they could move up into management, which is sort of the way it worked at IBM a little more. It didn't work that way so much at Bell Labs, so people would go off to universities. It was a nice way to get tenure. You do some nice experiments, and you don't have to be an assistant professor, which is a God-awful job. So, what I'm saying is that I remember that I had already started interviewing at places, including Caltech, for jobs to move away from Bell Labs in '95. I remember sitting in my lab at Bell in—I don't know--like September, and this announcement came over the PA system. "All employees, go to the auditorium."

ZIERLER: Uh-oh.

EISENSTEIN: Right, it scared the crap out of us. We all went to the auditorium, and they announced the creation of Lucent Technologies, and that we were all hereby, or at some date soon to occur, we were all employees of Lucent.

ZIERLER: Better than a mass layoff.

EISENSTEIN: Oh, yeah, it wasn't a mass layoff. That came—the layoffs came later. [laugh] So, I had already by this point had been interviewing heavily at Caltech. I don't know whether I had decided to go to Caltech at this point, or whether it was shortly thereafter, but I had a couple of job offers, Caltech being one of them. So, I had left before—I didn't leave until January of '96, I was already on the payroll at Caltech. Bell Labs was—allowed me—this is another illustration of what an amazing place it was. I didn't have a lab yet at Caltech, and I wasn't moving there yet. They said, "Well, you can just stay here. You can keep your lab. Here's $50,000 for expenses in the lab. By the way, we'll pay your moving expenses, all this kind of stuff. You can take all your equipment." It was unbelievable. It was unbelievable.

ZIERLER: Was Bell Labs a little more stingy toward the end of your tenure?

EISENSTEIN: Not more stingy but we began having discussions about who our customer was. [laugh] We were told that if we told—if somebody asks us that, like Arno Penzias or somebody ask us who are customer was, if the answer was Phys. Rev. Letters, we would be fired.

ZIERLER: [laugh]

EISENSTEIN: [laugh] We had to figure something else out. I'm just glad nobody ever asked me who my customer was because it would've been hard. I was in a department run eventually—I started off as Venky's postdoc. But Venky went off. First, he went to Santa Barbara, I mean, Sandia National Labs, and then he went to Santa Barbara. So, he was gone. I was in the department of a fellow named Federico Capasso, who's a professor at Harvard now. Federico just—he was as good as I could imagine. He never bugged me. I came to him once a year for my review, and told him what I was doing, and he said, "That's great." Well, I mean, I don't know how—whether he really thought about it very hard or not. But I was doing pretty well by this point then, and things were going well. But I wasn't doing anything that AT&T cared about, that's for damn sure. But it didn't have any impact on me really directly. People weren't being fired. I mean, there was always somebody getting fired but it had nothing to do with Judge Greene and the demise of the lab.

ZIERLER: Jim, what was compelling about Caltech for you at that point?

EISENSTEIN: Partly, you have to look at the alternatives. The alternatives were, at the time, I had applied for three jobs. One was Caltech. No, they came to me through a fellow named Michael Roukes in the Physics Department, who really was instrumental in getting me interested in Caltech. One was Brown University. I had a job offer from them. The other was Indiana University at Bloomington, which you could say, "Why were you interested in there?" That's not Harvard. It's a good school. It had two theorists that I knew extremely well, and still do. They're both gone from there. One is Steve Girvin, the other's Allan MacDonald, who were leading lights in the field that I was in. I was good friends with both of them, and still am. So, there was some appeal there to that. I remember when I—you know, making decisions are always hard. But the financial offer at Caltech was better than Brown and Indiana—not enormously so, but it was better. Let's see. Going to California was something Barbara and I, my wife and I always wanted to do. We like Berkeley. We've grown to like Southern California a lot more than we ever thought we would. I really—and not just South Pasadena but I really love Southern California, I really do. So, that was a very big appeal. The lab space that Caltech offered me was far and away better than anything that the other places were offering. I don't know. I don't know really. It seemed obvious at the time but I don't think it was totally obvious.

ZIERLER: I mean, did Caltech physics have a cachet in your mind as well?

EISENSTEIN: No.

ZIERLER: You didn't care about any of that?

EISENSTEIN: It had a negative one because—

ZIERLER: Negative?

EISENSTEIN: Yeah, because there's this—because I was ignorant of how things had changed. I thought it had the Murray Gell-Mann attitude. I knew there was applied physics, and the only person doing molecular beam epitaxy at the time, a guy named Tom McGill, was in the Applied Physics Department, and Murray Gell-Mann made statements about squalid state physics, and just stuff—ridiculously stupid stuff like this. Caltech can be a very stupid institution too, like every place.

ZIERLER: Parochial?

EISENSTEIN: Yeah, not just parochial, just stupid. It can do really dumb things, like every place can, and that was incredibly dumb. It was a disease that—Princeton suffered from it. Harvard suffered from it. Yale suffered from it. And Caltech had it too.

ZIERLER: But with your appointment in physics, not applied physics, was that a good sign?

EISENSTEIN: Yes, it was. In retrospect, it was a good sign that they understood something that they hadn't used to understand.

ZIERLER: Who do you credit for that? What's the post-Gell-Mann transformation that makes that possible? Is it John Preskill?

EISENSTEIN: No, I don't know the answer to that. Certainly, I was not the first condensed matter physicist. There were a sprinkling of a few others: a guy named David Goodstein who has retired like me. He's older than I am. There was—they had hired Michael Roukes, who was in the same general area, very generally speaking, that I am in. They had a young, at the time, assistant professor, Nai-Chang Yeh. She's still in the department. She's obviously a professor now. But who's—I don't know the answer to this question, I really don't. But I do know, I've served on enough committees or did—I don't anymore, thank god, but I served on a staffing committee, for example, for a long time, the hiring committee—to know that there's a deep-seated understanding of the value of condensed matter physics that this Murray Gell-Mann thing, this is not there. Maybe it was never really there. Maybe it was always kind of a cartoon, and it was just him. But it's not there anymore. The condensed matter appointments that we tried to make, and did make, got enthusiastic support from Preskill, Mark Wise, Hiroshi Ōguri. These are all high-energy people—or Preskill used to be, right. So, this just wasn't there anymore. I knew more about Caltech's Astronomy Department than I did about the Physics Department because I used to be really interested in astronomy. Anybody that owned the 200-inch Palomar telescope was OK for me.

ZIERLER: [laugh]

EISENSTEIN: As a kid, that was like the dream world for me as a child.

ZIERLER: Jim, in setting up the lab at Caltech, where is there opportunity for continuity from Bell Labs, where is there opportunity, new environment, new institution, opportunity to work with students, let's try new things?

EISENSTEIN: I'm not good at that, that's the bottom line. I felt, you know, this was a big challenge for me and, at some level, it was a risk. Bell Labs is—a lot of smart people there. They weren't any smarter than the people here. They weren't any less smart. But there was this self…there was this reinforcing going on all the time at Bell Labs, which is not here. Every day, I sat at the same lunch table with the same crew of people that were leading lights, many of them, in condensed matter, various areas from applied things to not applied things. I had lunch with Pierre Hohenberg most days of the week. You can't help—unless you're just deaf or stupid—you can't help but benefit from that. They make it easy for you to succeed. It's not that it's not tense. But if you can't succeed there, it's not because they didn't give you the opportunity. You had so much internal support.

And here, you know, Caltech maybe less than other institutions—I don't know—but professors are little Napoleons. They have big groups, and they're running around paying attention to them. There's no lunch group that I ever went to here. That's probably more a statement about me but I didn't have any trouble with it at Bell. I used to go to lunch every day with all my friends and colleagues, and we would—you know, somebody would drop a—I'd say something stupid like, "I don't know what's going but I can't get the magnesium to work right." Somebody would say, "Oh, did you do this?" Oh, 10 seconds, problem solved. That doesn't happen here. At least, I've never had that happen here. It's a very different kind—university academic life, for me, was fundamentally different.

ZIERLER: Jim, did students, graduate students, postdocs, did they fill that void at least socially for you to some degree?

EISENSTEIN: To some extent, yeah, certainly. I had some—I like to say that I had great graduate students because I didn't have very many. I'm not—I was not an empire builder type. You see some of these groups at Caltech and elsewhere, condensed matter physics groups with 50 people in them. When I was a kid, this was inconceivable. So, I had five people or six people in my group. The biggest it ever got was six people: two postdocs, and four grad students. That's what I felt comfortable with. I need to understand everything that's going on in my lab. If I had 50 people, there's no way in the world that you can understand everything that's going on. I couldn't anyway. My brain is not nearly big enough for that. So, I knew exactly what all my students were doing. I never had group meetings because I didn't need them. I probably should've had them so the students could talk. They talked anyway. They could have the advantage of the meetings. I would occasionally try to start them up, and they would always kind of piddle out after a few weeks because I was all—and you can ask my former students. Probably, they'd say, "Yeah, he pestered the daylights out of me," because I always wondered, "What are you doing? What? Do you understand it? What is this?" I really wanted to know what they were doing. I was very involved.

Back to top

Caltech and Project Q

ZIERLER: Jim, coming off the Bell Labs gravy train, how was it when you had to come up with your own research funds again?

EISENSTEIN: Pain in the neck, obviously, but I was successful, and I tried to get by—and I did because I had a small group—on the smallest amount of money possible to do what I wanted to do. I had no desire to get more money than I could handle because of the same thing: that I didn't want to become a money manager. With 50 people, somebody has to figure out how to pay their salaries, and buy them the equipment, and so on and so on and so on, and it becomes an enormous managerial job. I didn't want to do that. You can tell by when I retired, I went into--what did I do? I went into the lab, and started turning the knobs, and doing experiments, writing papers. I wrote four papers without—where I was the first author, which is—you know, you don't do that as a professor, typically.

ZIERLER: Was it all NSF or was big tech starting to get involved?

EISENSTEIN: I had an NSF grant all along. I finally canceled it because I said I knew I was getting near the end, and I said, "Not going to renew it." I had a DOE grant about the same size as the NSF grant. They were quite good too, and I canceled them out too after a while. I remember once I had a frustrating conversation with my DOE manager, and he said, "Well, you're not publishing very many papers." I said, "I'm publishing the same number per year that I've always published. Look at the statistics." It was true. In fact, even the year he asked, I actually had an excess. I said, "I don't publish very many papers, and it seems to be working for me. But that's all you're going to get because a lot of people feel required and do publish far more—far more—than I did." I found that discussion worrisome. I said if he's—he was a good guy. I'm not going to say he wasn't trying to do his job well. He was. But if somebody's taking a count of how many papers I'm writing, as opposed to what those papers are, I'm in trouble. You can understand that. That's simple enough. So, I had a DOE grant about the same size as the NSF grant—then, in 2005, we haven't discussed this yet but there was—2005—NSF—not NSF—Microsoft got off on this idea of quantum computation called topological quantum computation. You've heard about this?

ZIERLER: Yeah.

EISENSTEIN: You know about Project Q?

ZIERLER: Yes, yes.

EISENSTEIN: OK. So, I had funding. The initial Project Q, when it first started, had a substantial—I guess it still does—a substantial experimental activity but it was devoted—believe it or not—to the quantum Hall effect. Can you believe this? The reason being, once again, it's—I told you the quantum Hall effect was a watershed event in physics in so many ways. There was a recognition coming out of theoretical work starting by a guy named Nick Read at Yale—great guy; brilliant math…a very mathematical guy—that there were quasiparticles in quantum hall systems that could behave not like bosons or fermions but something else. Not only—we already knew that. But he said, "No, no, no, I don't mean that. I mean really different." "What do you mean?" Are you familiar with this word "anyon"? Ever heard this?

ZIERLER: No.

EISENSTEIN: OK. So, you do know there's a Pauli exclusion principle?

ZIERLER: Mmhmm [yes].

EISENSTEIN: The Pauli exclusion principle says many things. One of the things [laugh] it says is if you exchange the position of two electrons in a system, the total wavefunction will change sign. It must, in fact. That's the consequence of the Pauli exclusion principle. If you exchange two electrons and all their quantum numbers, it will change sine. If you have two bosons, like two helium-4 atoms, and you exchange their wavefunction, it will not change sign. It will be multiplied by plus one. Nothing will happen. That [remained] until the quantum Hall effect, really until 1983. The world was built out of that understanding that all particles in nature either came in one category or the other. There was nothing else, OK, bosons and fermions. The fractional quantum Hall effect came along. This is not the quantum Hall effect. It's fractional quantum Hall effect. Lo and behold, there were stable quasiparticles believed to exist in quantum Hall systems that when you took two of them, and you interchanged them, the wavefunction got multiplied by a complex number; not plus one; not minus one – . This was a big thing. There were some early theoretical ideas that it might happen in two dimensions, could never happen in three dimensions because of some mathematical results that I don't understand, but could happen in two dimensions.

These things are called anyons because their phase could be anything if theta didn't have to be zero or pi. It could be pi over 2. They've only recently been verified that this actually exists, but it was predicted theoretically—very exciting. What Nick Read found—and our colleague at Caltech, Alexei Kitaev, made use of—was that there was still another possibility, and that was that not only if you took these particles, you interchange them. You didn't just change the wavefunction by some complex number or plus or minus one, you got a whole new wavefunction, a completely different thing. Think of it as a vector. If the vector is like this, and you multiply by minus one, it's like this. You multiply by plus one, nothing happens. If you multiply it by a phase, you get some complex number. So, if you squared it, it would still be one; still be the same. For these other things, point somewhere else in Hilbert space, it can be a different wavefunction altogether. These are called non-abelian quasiparticles—a fancy word; fancy stuff. Alexei Kitaev realized that you might be able to store information and do computation using these non-abelian anyons in a way, but because they were so protected by this peculiar property that they had—it's a topological property in the end—that the normal disturbances of life that make quantum computation so difficult to actually do wouldn't have much effect, or would have a greatly reduced effect. So, you should talk to John Preskill about this. He'll talk to you about quantum error correction, and if you don't have topological quasiparticles, you're going to have to do a lot of quantum error correction to make a quantum computer work. But if you somehow got these topological things to work right, magic would occur, and you could get away without doing so much error—so, what's the story? Well, Microsoft fell for this. They fell for this because there's a brilliant math…a Fields Medal mathematician, a guy named Mike Freedman, who works at Microsoft—sorry, I'm getting tired now—but he works at Microsoft, who told the managers, "We got to do this. This is the future of computing." They bit. Where does this—where was the first possible physical system? Fractional quantum Hall effect, in fact, the particular fractional quantum Hall effect state that Bob Willett, Horst Störmer and myself discovered in 1987. So, I was a natural to be part of this group on the experimental side when they opened up a program, and they had deep pockets, and they gave us a lot of money. It doesn't work because it doesn't—it hasn't worked, I should say. It's just too demanding on the material side. It's just going to take forever to get this to work.

ZIERLER: Jim, were you involved in IQI from the beginning?

EISENSTEIN: No. No, and in fact, I—with John, actually, there was a progenitor, a precursor to IQIM, which we called CEQS, the Center for Exotic Quantum Systems. It was going to be an NSF institute devoted to exotic matter, fractional quantum Hall physics, other emergent phenomena in solid-state systems and material systems, without a particular focus on quantum computation and quantum information. That has since gone away, and morphed into IQIM, first with—what's his name? Oh, boy. Well, John is the second director. Jeff Kimble was the first director, and he stopped doing it after a while, and John took over. It's, like I told you at the very beginning, it's IQI. So, I don't know how we got—how did we get to this? Anyway, Microsoft gave me a lot of money, and it lasted for five or six years, with amount of money that was twice what NSF was giving me. We tried studying this particular fractional quantum Hall state, and we did, learning more and more about it because the Microsoft guys, in my opinion, did not have a realistic understanding of the world of material science; that materials are complicated, and stuff goes wrong, and there's stuff you just can't control without enormous effort. So, they eventually gave up, essentially, on the quantum Hall version of this idea of topological quantum computation, and now they're off into something called Majorana fermions, which you've probably heard the words too. The fractional quantum Hall system had Majoranas in it as well, but this is in a different material system, a completely different kind of phenomenon, and they're putting in—I actually lost track, so I don't—maybe they've even sto…I don't think they've stopped. But I don't know where Project Q is anymore, but they are invest…they have invested an enormous sum of money into this.

But I backed out of it in 2011. I said, "This is not—I don't want to do this." They were—the initial discussions with Microsoft was, "You know, all we really want to do is get a reputation for Microsoft as being a good place to do fundamental research. That's not our reputation now. We'd like to try to build that up." Well, that sounded good. They give me a lot of money, and all they want is PR. Well, that's not—of course, that's not really what they wanted. Eventually, they wanted what they said this is. They want to rewrite computation someday, and they have an enormous effort in it.

ZIERLER: When you say "rewrite computation," do you mean quantum computation?

EISENSTEIN: I mean, get rid of, I mean, to supplant classical computation with topological quantum computation. Now, whether they've broadened that focus, and have a greater recognition of the difficulty of that and, well, maybe even have a secondary effort or another effort on what I might call conventional quantum computation, using non-topological things, I don't know. They may.

ZIERLER: Jim, circa 15 years ago with Microsoft, was this already a horse race between IBM and Google, Amazon, or was Microsoft out in front this early in the game?

EISENSTEIN: OK, so, 15 years ago, none of them were doing it. Was Microsoft the first company to start working on the idea of topological quantum computation?

ZIERLER: Yeah.

EISENSTEIN: Yes, as far as I know, yes. Were they the first corporate entity to start pushing quantum computation? I suspect the answer is maybe no to that, but I'm not sure.

ZIERLER: Do you—?

EISENSTEIN: John would know that.

ZIERLER: Do you have a sense internally at Microsoft who was driving this?

EISENSTEIN: Not really. I guess, you know, I'm not a Microsoft employee. But they had this very famous mathematician, this fellow, Mike Freedman, and he won the Fields Medal for whatever he did—some—one of his famous mathematical problems that he solved. I sort of figured, well, they're just trying to keep their most famous mathematician happy. But it's way beyond that now, I mean, way beyond it. I think the amount of money that they have spent on this project is not in the tens of millions; it's in the hundreds of millions.

ZIERLER: Yeah.

EISENSTEIN: So, it's an insanely large amount of money. But, as I say, it was 2011 I really separated from it. I continued to go to the meetings for a few years, but I don't any longer. The pandemic came, and all that stopped. Maybe I went a little longer than 2011. I can't remember. But I've been away from it for a long time.

ZIERLER: Just to back up a few years, what was it like when you won the Buckley Prize in 2007?

EISENSTEIN: It was fun. We went out to dinner. [laugh] That was fun. Obviously, it was very gratifying. I won it—by the way, I shared it with these two fellows that had been at Indiana University, Steve Girvin and Allan MacDonald.

ZIERLER: [unrelated conversation]

EISENSTEIN: So, we shared it together, and I've been friends with them for so long, so it was very, very nice. I don't know what else to say about it. It's a nice thing when you get recognized.

Beware Hype in Science

ZIERLER: Yeah, especially, you know, the Buckley Award in Condensed Matter Physics, that's really one of those awards where it's a deep understanding by your peers in your field.

EISENSTEIN: Oh, yeah. Oh, yeah. Yeah, and somebody has to nominate you, and then it's a big—because I've been on the selection committee. One of the things you get when you win the Buckley Prize is you get to help pick the next one—

ZIERLER: Yeah. [laugh]

EISENSTEIN: —and the next one and the next one. They come to you to be on the committee, and I've done it a couple of times. When somebody comes forward and nominates somebody, there's a big case built up. I won't say that everybody that's won the Buckley Prize—well, I guess I would say. Everybody that's won it has deserved it, but not everybody that deserved it has won it. That's kind of obviously true.

ZIERLER: Absolutely.

EISENSTEIN: But it was—

ZIERLER: Like, even with the Nobel Prize, every single Nobel Prizewinner has not done equally significant research.

EISENSTEIN: Of course. Of course, that's true. So, I was very gratified by it. It made me feel good, yeah.

ZIERLER: Now, when you pulled back, as you say, a little bit in 2011, how much of that is about the hype around quantum computation?

EISENSTEIN: Well, as I told you, I'm a grumpy, old man, and I dislike things, I dislike hype, but I've always disliked it. I don't think that was why I decided to back away from that. I felt like what I was really interested in doing research-wise was not what they wanted. For example—

ZIERLER: So, where were you? Where were you at that point?

EISENSTEIN: What do you mean where? In research?

ZIERLER: In research, right.

EISENSTEIN: I'll tell you. When I got the Buckley Prize, that was during the time that I had money from Microsoft. The research for which I won the Buckley Prize predominantly—although not exclusively—was on subjects that had nothing to do with Microsoft's interest. So, they saw—I mean, they can look at that. In fact, I even got a message from some VP at Microsoft after I won the Buckley Prize. "Congratulations. That's really great work on bilayer two-dimensional electron systems." Well, that's not topological quantum computation. Once, I had to give a seminar to the Microsoft guys, and I was warned in advance, "Don't talk about bilayer two-dimensional electron systems." So, what they wanted from me was something that I didn't feel I was (a) making enough progress on, and (b) I wasn't willing to—what they would've wanted me to do was to stop working on everything else, and work on this. They were devoting tons of money, and they expected—I felt—this is my perception. They wanted full-time commitment, and I wasn't willing to do that. So, we parted on very friendly terms. They had given me a lot of money, and I acknowledged them whenever it was appropriate. But the things that—their focus was shifting away from the quantum Hall effect toward these Majorana issues, and I could see that, and I said, "Come on, Mike." I talked to Mike Freedman out on the grass in Santa Barbara, and I said, "I'm not doing what you guys want to do, I'm just not. I don't want to feel like—I got a lot of money from you guys, and I'm not spending it the way that you want." That was the end of that.

ZIERLER: When you served as an editor for the Annual Review of Condensed Matter Physics, this is really toward the end of your—are you starting to think about retiring? My question there is, does that give you a more bird's eye view of what's happening in the field? Was that useful for you?

EISENSTEIN: Oh, for sure. Oh, it was helpful, yeah. We would have a meeting at the March Meeting, the editorial board. We'd get together, and we'd think up people to invite to give reviews. Can they write reviews? Of course, the committee's very diverse. I'm doing one kind of thing, and then there'll be somebody doing soft matter, or there'd be somebody doing computational physics, and various kinds of people. I had to think a little bit about the people they were nominating, whom I didn't know anything about. They talked to me about, well, there's—take an example, somebody we got an article from, a fellow named Steve White. He's a theorist at Irvine. I think it's Irvine. He's not that far away from what I do. But he's a numerical kind of guy; does calculations of physical properties using very sophisticated computer techniques, and he's invented many of them; something called DMRG. What's it called? Something Monte Carlo. I forget what all the letters stand for. Renormalization—I forget. It doesn't matter. So, I had to learn about that enough to understand the nomination of this guy, and it took like 10 minutes to realize, yeah, we got to have this fellow. There were liquid crystal people. I don't know so much about that. So, that was fun. But it was also work. It turns out it's not just—you don't just go to this thing, and they feed you your lunch. That would be one thing. You actually have to then contact the people, and you have to pester them; find out whether they're really doing what they said they would do. "Did you really write the article? Is it coming some day?" I'm not a big fan of that, but I did it for a while. It was good. I also served on a number of committees. I helped write the Decadal Review of Condensed Matter Physics, one of the previous Decadal Reviews. Boy, you learn a lot about other things going on that way.

ZIERLER: Oh, yeah.

EISENSTEIN: That was OK. I thought that was—the output was not commensurate with the input—but still. I served on the Solid State Sciences Committee, and Board on Physics and Astronomy for a while; those kinds of things. So, you're forced to learn about—a little bit about what else is going on, and that's very—that can be stimulating, and you meet people.

ZIERLER: Jim, because you've never had a large number of graduate students, probably one of the advantages there is getting to know the few that you've had very well.

EISENSTEIN: Right.

ZIERLER: When you started to think about retiring, that has such obvious and clear implications for your graduate students, is it important? Do you break the news to them first? How do you go about just in terms of getting the word out there?

EISENSTEIN: Well, graduate students, I always had good graduate students. I knew when they were all going to finish because I could—I mean, I could make a good prediction when they were going to finish up. So, I phased everything so that when I retired, everybody would be finished, which meant I had to stop hiring people about six years before I retired because that's how long it takes to get a PhD.

ZIERLER: Right.

EISENSTEIN: Every one of my students took six years, every single one; very periodic: six years. So, I knew that if I were going to take another one, it was another six-year commitment. I wasn't going to leave one hanging in the wind. If I had a student, I was going to see him through to their next step in their career. I wouldn't retire—

ZIERLER: So, who was the last? What year was the last student you took on?

EISENSTEIN: Let's see. This was a woman from India who now works at Intel Corporation, who I think I hired in 2009, and I retired in—I didn't retire but I went on this leave, this preretirement thing that I told you about, at the end of 2015, six years later. She was just out the door.

ZIERLER: Yeah.

EISENSTEIN: The two postdocs I had at the time were just out the door. Literally, I had it—I'm kind of anal retentive about this kind of thing. I had it planned out very accurately, and nobody was left stuck. Nobody had to—

ZIERLER: Was part of the grand plan so that you'd have these precious few years in the lab to yourself?

EISENSTEIN: Oh, yeah. Oh, yeah, very much so. I found out that—two things. One is I could still do experiments. Not two things; three things. I wasn't as young as I used to be, it was harder, and there's a lot of smart young people out there in the world doing really good stuff. It's a vanity to think that just because you're very experienced that you can keep up with these guys without a big staff of people, even though those young people that are working for you are slower. You understand what I'm saying? I couldn't—there's no way I could keep up, no way. So, I said I don't care. I'm going to work on things that they don't care about. But, after a while, you realize that's not really the way to do things.

ZIERLER: Where is it about physical energy, and where is it about mental energy at that stage in your career?

EISENSTEIN: I got other things going in my life too, you know, grandchildren and all that kind of stuff. The pandemic was a big stinker. If we were having this discussion, and there hadn't been a pandemic, I don't know where I would be right now. I might still be slugging it out in the lab by myself, with the graduate students across the hall in another group looking at me like I was out of my mind, because I was literally alone. I had no techs, no students, nada.

ZIERLER: Did you find yourself asking fundamentally different questions that you had asked at Berkeley, at Bell, in your earlier career at Caltech?

EISENSTEIN: Do you mean scientific questions?

ZIERLER: Yeah. I guess that's a way of saying what had been resolved at that point, and what was still wide open?

EISENSTEIN: I told you that I'm not good at reinventing myself.

ZIERLER: But you have to write new papers—

EISENSTEIN: Yeah, you do.

ZIERLER: —and still do science.

EISENSTEIN: Yeah, but you can write a lot of papers, you know, what you would call a narrow area where you are certainly…someone could say, "Those are exactly the same as your papers you wrote 30 years ago."

ZIERLER: [laugh]

EISENSTEIN: They haven't changed... [laugh] They wouldn't really be wrong about that.

ZIERLER: [laugh]

EISENSTEIN: Again, this is the old man in me speaking, but there's a big tendency in physics, and I'm sure it's true in all sciences, what do you want to do? You want to make a big hit. You want to find something that nobody's seen before—that's important—and you want to do it first, and I oftentimes don't want to get stuck in the details afterwards. This happens a lot, and I don't like that, although I definitely played by that rule, certainly at Bell Labs. You had a merit review every year. One of my most important personally satisfying paper was a 25-page PRB that my manager, Federico, wanted to know why I wrote. Well, I know why I wrote it, and it was important, and it got a lot of citations, so the field felt that it was important. But it wasn't important to the management. So, I have always wanted to kind of understand things, and the work that I've done, you can discover something and still not understand it for a long time, or ever maybe.

So, there's always things to figure out more. I'll give you an example that's been a big example in my life, just to cut to the chase. So, a two-dimensional electron system over here, a plane surface, electrons running around, big magnetic field around, another one over here. I bring them close together. What happens? Well, I don't know. The electrons in one layer start to see the electrons in the other layer. They're not too far away. So, they start to stay out of each other's way because they don't—electrons repel each other. Something new can happen. In fact, it turns out that an entirely new phase can appear when they get close enough together—this is one of the things I won the Buckley Prize for, along with Girvin and MacDonald—an entirely new phase, something called excitonic superfluid, which had been thought about for 40 years, and we discovered it in a particular context for the first time, and wrote a lot of papers about it. Several of my grad students were involved in it. It was really exciting physics—still isn't very well understood. At a qualitative level, everybody think…if you ask your average condensed matter person if they've heard of it, they'll say, yeah, they got that. That's understood. Not understood, not really. How does this transformation occur? Does it occur like that like water decides to go from liquid to solid when you cool below 32 degrees Fahrenheit, the first-order phase transition? Boom. You don't even know it's coming. If you're at 32.1 degrees, you don't know that one more tenth of a degree, everything's going to solidify, but it does. In this case, you bring these guys together, and you don't know. Is it going to do it abruptly or continuously? Is there really a phase transition there, or is it some kind of crossover effect?

So, this physics has been around—I'm embarrassed to say—for 30 years. I've been working on—among other things—I've been working on this kind of problem. Bert Halperin just wrote a paper last year with a new approach to understanding what happens as you bring these stupid things together. So, it's obviously not understood. Now, there's 25 other papers saying what happens as it gets closer together. It's obviously not understood. I was working on—the stuff I did toward the end of my experimental work was trying to see if I could tell that this was coming before it came. In other words, I wanted to get to 32 point…the analog, get to 32.1 degrees. Is there anything showing up that suggests that something big is about to happen? It turns out there is. It turns out there is, and it's conceivable to me, although Bert's a very careful guy. He almost never—he dislikes the i…you probably got this from him. There's a lot of funny stories about Bert Halperin. I'll tell you one in a minute. But he doesn't like to speculate without a really good reason. I said to him—because this was just maybe even six months ago. I said, "Bert, this new idea that you have, is that related to those measurements that I just did and published in PRL about two years ago, year and a half ago, whatever, that showed something was beginning to happen?" He goes, "Possibly. [laugh] I can't calculate it though." He said, "I don't know how to approach that yet." Some smart person will come along, maybe, and figure out how to approach it. But Bert said, "I can't do that yet." Oftentimes, this happens. You can measure one thing, and it's not the theorist—it's not the thing that theorists know how to calculate. They calculate some things, and it turns out you can't measure those. It's pretty common if not universal that that happens. So, that's been an interest of mine, and I would say that the bulk of condensed matter physicists, they've moved on to other things, and they don't—if we find out something dramatic in the future related to this transition behavior, then they'll wake up again for a while.

ZIERLER: But that requires people to stay working in this field.

EISENSTEIN: Yeah, and there are others. There are a few other groups in the world that have worked on this problem. A fellow, a good friend of mine—well, not a good friend but he's a friend of mine, Klaus von Klitzing, in Germany, he won the Nobel Prize…he discovered the quantum Hall effect. He's an important guy. He devoted a lot of his effort in the last 15 years to the same physical problem, and done some very nice work. He's retired though in Ger…whatever the German way of retiring Nobel Prizewinners is, which is a little obscure. So, he's there. There's a group in Japan, a young fellow, a guy at Princeton, still interested in it a little bit. So, I'm not the only person but it's a small—when we first saw the effect back in the early aughts that the exotic properties that occurred once these layers got close enough together, and I won the Buckley Prize, and a consequence of that was everybody was paying attention. It was exciting. It was really exciting. But now they're on something else, and the same thing will happen to people who are working on the something else. They'll find out that it's not so well understood as they thought, and old guys like me will say, "Well, we got to make more measurements, and so let's look at it more carefully," and so it goes, right. [laugh] This is the story of life. [laugh]

ZIERLER: There's a circularity here, I'm detecting.

EISENSTEIN: Yeah, of course. I did not—I was not good at reinventing myself. I didn't ever see the need to, which is both a virtue and a curse.

ZIERLER: But it also speaks to the richness of the field, that there's so much to mine, even in the small area that you're working in.

EISENSTEIN: Absolutely. Take this young fellow, Joe Falson, who's just started, he's got new ideas for how to do crystal growth of weird materials that we don't really have yet or we don't have them in ways that would make them useful to do—for doing an experiment. I bet you he's going to come up with ways to do these things, and I bet you it's going to—people are going to be surprised at the cool stuff that comes out of it, and it's materials again. It's materials.

ZIERLER: Jim, we started this conversation by talking about your current interests, your current work.

EISENSTEIN: Oh, yeah.

ZIERLER: We're coming full circle now. For the last part of our talk, I'd like to ask a few broadly retrospective questions about your career and research. So, first, on a very basic level, it's been such a technical and narrowly focused discussion because that's just the nature of your research career. Let's zoom out.

EISENSTEIN: OK.

ZIERLER: In terms of your findings, in terms of your contributions, beyond physics even, just about nature, how we understand nature as a result of the work that you've been involved with over the course of your career, what do we understand now that we didn't, going all the way back to when you first figured out how to be a scientist at Berkeley?

EISENSTEIN: That's a loaded question. That's a hard question, (a) it's hard, and (b) the answer's going to be so disappointing. I don't know. I guess what I've learned more than anything else is that—I mean, this is going to sound ridiculously trite—but nature's bag of tricks has no bottom.

ZIERLER: [laugh]

EISENSTEIN: It just doesn't. I've learned that, like I told you, that the periodic table is a rich thing. I think it is also true that physics is very poorly understood by the public. This is another hobbyhorse of mine. When you ask somebody about physics, it used to be they wanted to know if I made bombs, you know, long ago. Then they wanted to know did I have something to do with that thing—what's that thing called?—LHC I heard about in the newspaper? I would say, "No, I don't do that." "Well, what do you do?" I would say, "Well, I work on materials in trying to understand how materials work." They go, "Oh, well, oh, so, you're like a technologist?" I go, "Yeah, I'm a technologist," because they don't understand, people have no clue that physics is more than the stuff that The New York Times tells them it is, and most people don't even read The New York Times, obviously. What do you see in The New York Times? Oh, they just found out at the LHC that the Higgs boson was there. Well, I would've said it would've been a lot more interesting if they hadn't found the Higgs boson; if they'd found something else. That would've been a way bigger deal.

ZIERLER: Sure.

EISENSTEIN: Or they want to know—and it's just…here, this is much more justified. What you find out in the world of astrophysics and astronomy, you can't—condensed matter physics cannot compete with that in the public view. I tell them that there are things called topological insulators, and they think, "Oh, that's the kind of guy I don't want to invite over to a party. He'll start talking about that stuff, and nobody will know what's going on." So, physics is extremely poorly understood, and this poor understanding is—I guess it's the field's fault but it's also the way it's reported. If you do something in the area where I work, general…broadly speaking, your best hope is that you're going to invent the transistor. Then they'll remember you as the person that made this technological discovery that they no longer think about but there's a billion of them or 10 billion of them in here. And, oh, well, you know, just what's next? What have you got for me this week? But this is all solid-state physics. You know that. It's all the 20th century's—last half of the 20th century trying to figure out how silicon worked. So, the stuff that I do is in that general area, and it's not understood by the public. I try very hard, when I give public lectures…I can give a good public lecture, and I think people kind of like it. But it's hard to compete with the stuff they hear on a daily basis what it is that scientists, physicists do. They don't—condensed matter physics is just too remote. I wish that—I would love to solve that problem somehow. I didn't really answer your question. But the richness of material science is what I've lived off of, and society in its own blasé way also lives off of. They just maybe don't recognize it. They don't recognize it.

ZIERLER: What's the most fun you've ever had in science?

EISENSTEIN: Oh, I can tell you that easily. I've had it numerous times. It's the day you see something that nobody's seen before, and you know immediately that it's important, in a relative sense. You know, oh, my god, that's amazing. I did this, and it happened. That provides a thrill that, for me, is the ultimate. I still remember that—this is an example of that—I had an outstan…my first graduate student, again, one of these great students, a fellow named Ken Cooper who now works at JPL, absurdly smart guy, did some beautiful work as a graduate student. But it was very—the work we had to do involved a lot of measurements, and they were time-consuming. He was religious about doing them and keeping good records. But there's a limit to how many hours there are in the day. So, he would look at many samples grown by our crystal-grower friend who was still at Bell Labs at the time, and he would look at them at a temperature of 50 millikelvin. Why? Because you could do so a little more quickly there than if you tried to cool it to 10 millikelvin where you had to be very slow, that you didn't inadvertently heat up the sample so things—if he had to do what he had done at 10 millikelvin, he'd still be a graduate student. He didn't do it. So, he went away. He had a sample in the refrigerator, and that was—I think it was—actually, it was around September 11th, believe it or not. He went away for a few days' or a week vacation with his wife. I said I'm going to just spend some more time with that sample, and I'm going to cool it to 10 millikelvin. I don't have anything else to do. I might as well. We made a discovery. It wasn't a big, important one. But it was something that turned on, believe it or not, at 40 millikelvin, and he missed it. I remember that day. I came in the lab. I took this long run overnight, and I came in in the morning. It was sitting there on the computer screen, and I basically said holy shit, that's amazing. I immediately knew that it was a discovery. That used to make me feel really good; not that I beat my student to it but that I saw something that nobody had seen before, even my friend Horst Störmer had not seen before.

ZIERLER: Jim, I think that's a pretty good answer to the previous question about what we understand about nature that we didn't understand before, by definition.

EISENSTEIN: Yeah, yeah. Bell Labs used to have this—I remember how amazed I was when Venky took me on my interview, and he said, "First we got to go down to the lobby." I said, "What's in the lobby?" They had like this display of all the big things that Bell Labs had done over the decades. There was a little exaggeration in there. But, I got to tell you, you went through that, and after a while, your jaw just slid down by your shoes, the stuff that had gone on from Telstar to fiber optics to lasers to transistors, all these things. I remember thinking this. I said, "This is just unbelievable." Then right next to this display was a bust of you-know-who, Alexander Graham Bell. Underneath it, there's a little expression from him. Again, it's almost trite. I don't remember the exact wording but it was something like, "Go off into the woods. You'll find something you've never seen before." Something like that; along that line. That's a principle to live by in science. It's trite but it's—

ZIERLER: It's real.

EISENSTEIN: —accurate. It's real.

ZIERLER: Jim, last question, looking to the future.

EISENSTEIN: Sure.

ZIERLER: Since it remains a bit of an open question whether you'll be an active participant or not, either on the sidelines or hopefully maybe you'll get back into the lab, what are you most curious about? What are the unanswered questions out there that you either want to be a part of or want to see as they continue to develop?

EISENSTEIN: I guess the answer to that is I'll be very interested in seeing—because I'm pessimistic about it—how the quantum computation revolution really unfolds. Are we actually going—and I'm not talking about topological; I'm talking about just the general problem. Are we really going to reach nirvana where we can make computations of things that we never could before or not? That's not something I'll be involved in but I'll be interested in the outcome of that, for sure.

ZIERLER: This is a timescale in decades, you mean?

EISENSTEIN: I think so. John Preskill could give you a more accurate but biased answer to that. Are they really going to solve big, complicated, many-body problems that you can't solve using Steve White's algorithms—Diffusion Monte Carlo or whatever the hell it is—because they've got a quantum computer that can solve things in polynomial time as opposed to exponential time, or whatever it is? Are we really going to do that? I'm not intrinsically interested in the—what do you call it?—the cryptological aspects of quantum computation, even though those may turn out to be most important for society. I don't know. But there are ideas that you could solve, big physics problems that you can't now address. Will that really happen? As I say, I'm pessimistic. But I could be wrong. Who knows? So, that's one thing. The other is material science. Just keeping watching, and I know these young guys are going to do cool things with weird materials, and they'll make big discoveries. I think that follows like night follows day.

ZIERLER: Things will still be interesting, that's for sure.

EISENSTEIN: Yeah, no question about it, yeah.

ZIERLER: Jim, I want to thank you for spending this time with me. It's been a fantastic conversation.

EISENSTEIN: Well, you're more than welcome.

[End of recording]