Nader Engheta (PhD '82), Physicist, Electrical Engineer, and Metamaterials Pioneer

In his thirty six years at the University of Pennsylvania, Nader Engheta has embraced a fantastically rich and diverse research agenda that operates at the boundary of physics and electrical engineering. It all centers around his fascination with structuring light, and the near-limitless possibility of discovery in basic science, and translating that discovery in applications that give rise to new materials, that enhance and broaden our communications capabilities, that advance stealth capabilities with new approaches in cloaking, and that improve optical accuracy by mimicking nature - to name just a few. In the discussion below, Engheta is explicit in crediting his Caltech education for such a daring and boundary-less approach to research, and for learning that the pursuit of discovery and understanding can never, and should never, be constrained by the administrative and even intellectual boundaries of disciplines and departments.

Engheta's appreciation for Caltech has a deeply personal dimension as well. After growing up in Tehran and excelling in engineering and physics at the University of Tehran, Engheta left for Pasadena in 1978, one year before the fateful revolution that upended Iran and the Middle East, and which poisoned relations between Tehran and Washington. On top of all the normal pressures of graduate school, Engheta was fearful for his family's safety, and he had no option to return home. In other circumstances, such isolation would have been perhaps too much to bear, but Engheta explains how Caltech, and especially his thesis advisor Charles Papas, ensured that he was well cared for and supported. This undoubtedly provided the foundation for Engheta's dissertation research on antennae and all that came after it.

In reflecting on his decision to spend his entire career at the University of Pennsylvania, Engheta explains that the qualities he admired so much at Caltech are also true of Penn, and his multiple appointments and affiliations across the University are testament to the relevance of his research across engineering, physics, chemistry, and biology. And despite the tremendous relevance and appeal of his science and technological innovations in the world of technology and industry, Engheta emphasizes that the starting point of his accomplishments is always curiosity. The simple wonder and striving to understand how nature works, and pursuing the questions and experiments to help answer the most important questions, explains not only Engheta's record of discovery, but also his sense of excitement for what comes next.

ZIERLER: This is David Zierler, director of the Caltech Heritage Project. It's Tuesday, August 15th, 2023. I'm delighted to be here with Professor Nader Engheta. Nader, it's wonderful to be with you. Thank you so much for joining me today.

NADER ENGHETA: Thank you so much, David. It's a pleasure to be with you, and I really appreciate the opportunity you have given me to chat about various aspects of life.

ZIERLER: Wonderful. To start, Nader, would you please tell me your title and institutional affiliation?

ENGHETA: Sure. I'm the H. Nedwill Ramsey Professor at the University of Pennsylvania. My primary appointment is in the Department of Electrical and Systems Engineering. But I do have secondary appointments in the Department of Bioengineering, Materials Science and Engineering, and Physics and Astronomy.

ZIERLER: Nader, who was or is H. Nedwill Ramsey, and is there any connection to your work?

ENGHETA: No connection. He was a Penn Trustee, and was the President of the Philadelphia Electric Company. I've never met him, I've never met his estate, but he had endowed this chair which I now hold, and I'm very honored to have it.

ZIERLER: Now, because of all of your affiliations within Penn, it begs a certain set of questions. First, fundamentally, are you an electrical engineer, or are you a physicist, or is the kind of work that you do, it requires a perspective that doesn't establish those boundaries?

ENGHETA: Excellent question, by the way, and this is a question that I am often asked, you know, by people when they become familiar with my work. I would consider myself both. I am both a physicist and an electrical engineer because, in my opinion, science and engineering are not separate from each other. They're completely intertwined. That's one of the things I've learned from Caltech, that there's no boundaries among different disciplines and different research endeavors. Yes, I consider myself both a scientist - a physicist, and an electrical engineer. As we go through some of the topics of my research today, you will see why, as we touch upon both physics, fundamental physical aspects as well as engineering and technological aspects of my work.

ZIERLER: Nader, what about experimentation and theory? Do you serve as your own theorist? Are there theories that serve as intellectual guideposts for your intellectual, experimental work?

ENGHETA: Excellent question again. By training, I'm a theorist, and I consider myself a theorist, although we do do experiments in my group. But we always start with a theory, and that is our center of gravity. We start with a theoretical aspect. We introduce new concepts. We study the concepts, both via fundamental mathematical aspect as well as computer simulations. Then in some cases, we do proof-of-concept experiments. As I mentioned, we do also conduct experiments in my group, but I would consider my group mostly a theoretical group with some experimental components.

ZIERLER: Nader, what are some of the most important theories that guide your work, that stay close with you, day in and day out?

ENGHETA: Another excellent question. To answer that, David, let me start by saying this, that I always admire the power of curiosity-driven questions, and I tell that to my students, postdocs and members of my group. Most of the time we start with curiosity-driven questions. I can tell you examples as we go through different examples of the research we have done. I love light, I love waves, and I'm passionate about the physics and engineering of waves, in particular electromagnetic and optical waves, like microwave and light. In order to utilize waves to have useful functionalities, we need to manipulate waves. We need to sculpt and control waves, and, for that, we need materials. That's one of the reasons that in my research activities over the years, I've been interested in various different material platforms that can interact with waves in very unusual ways that would lead to interesting and new functionalities. To come back to the answer to your question, yes, for me, electrodynamics is one of the great theories that I always work with and I always admire, combining that with materials science and engineering in order to control and manipulate waves leading to interesting technological features that will come out of it. In a short term, light-matter interaction is what I love.

ZIERLER: Now, you mentioned the importance of curiosity-driven research. It begs the question then, what aspects of your work are really purely basic science, fundamental research, trying to understand nature, and then because so much of your research has societal application, it is used to societal benefit, when is your starting point thinking about this translation, and then reverse-engineering the experiment or the idea?

ENGHETA: As I mentioned, usually I start with the curiosity-driven question. Maybe at the time I come up with the question, I may not have any application in mind. But when we get into to the nitty-gritty of answering that curiosity-driven question, more and more we get to the point when we say, "This is interesting." Really, we are trying to find out something fundamental about this interaction of waves. My experience over the years has shown that inevitably that gives rise to interesting applications. At that point, we connect our curiosity-driven question to the application aspects. Again, if time permits today, I can mention some specific examples as we go through this. Yes, I'm very interested in the fundamental research, and that connects us to some of aspects of applications, which we can talk about.

ZIERLER: Have you become personally involved in start-ups and entrepreneurial ventures, or when you have an idea that does have market applicability, you send that off to people in the business world?

ENGHETA: Good question. I have several patents on the ideas that we have come up with. In the past, a start-up started, not by me but by people who were interested in starting the start-up based on the patents that we had in the university. Many years ago, at the early part of my career, with one of my colleagues we started a small consulting company. It doesn't exist anymore. We just had it for a few short years. But that was just to look at some of the novel materials at that time. But, later on, as I mentioned, there was a start-up, not by me but by some people who started it based on the patents we have. That company does not exist anymore either.

Unbounded Research at Penn

ZIERLER: Nader, I wonder if you can talk about the state of interdisciplinarity at Penn. With all of your appointments, how does Penn institutionally encourage cross-pollination between professors, between departments?

ENGHETA: Very much encouraging, in fact, it's one of the great aspects of Penn, particularly Penn engineering here. I have to say that this is one of the attractive reasons I came to Penn, because it reminded me very much of Caltech—

ZIERLER: [laugh]

ENGHETA: —in that regard, really. Effectively, the boundaries among the departments don't exist. As a result, you can easily collaborate. That's very much encouraged, particularly interdisciplinary aspects. In fact, many colleagues do have secondary appointments in other departments, while primary appointments in one department, as I mentioned, like myself. Also, one of the interesting points, by the way, about University of Pennsylvania is that almost all departments of the university are in one location. They're not distributed over different parts of the city. With the exception of veterinary medicine, which some of its facilities are in different parts of the state, all other departments of the University of Pennsylvania are in one location. That proximity really encourages collaboration naturally. Just walk across the street, and you go and talk to a colleague. It's very much encouraged.

ZIERLER: Nader, you mentioned the importance of computer simulations. I wonder if you can reflect on the impact of all of the computational power that you've witnessed over the course of your career, how that's changed your research, and if you've become more involved or have even embraced recent advances in machine learning and artificial intelligence.

ENGHETA: A very good point. I'm always telling my students and postdocs that during my lifetime we have come a long way in various computational aspects. When I was an undergraduate back in University of Tehran in Iran, I remember, I think maybe I was in the second year or third year, that the calculators, I remember, Canon Company calculators were coming out, and they were doing four operations. I remember there was also one key to find the square root, and to us that was amazing. We were asking: "How does this gadget can take the square root?"

ZIERLER: [laugh]

ENGHETA: Now where we are, and you can imagine within our lifetime, we have come a long way. Clearly, that has positively impacted many, many research endeavors, and we see that in every aspect of every day of our lives, both scientifically and also personally, how the power of computations has really changed the world. This is another reason that one of the areas of my research activities in light-matter interaction directly relates to the concept of computation with light. I'm very passionate about that because that is, I think, something that can really open up quite a fascinating possibility. I also have to mention that at University of Pennsylvania, I'm in the building called the Moore Building, and my office is on the second floor. When you go to the first floor of the Moore Building, you see one piece of the ENIAC, the computer that was invented in the basement of University of Pennsylvania in 1946. I like the history of science, and I'm inspired by the fact, that I'm in the building where the ENIAC was invented, and I myself have an interest to use light for computations. But to finish my answer to your question with regard to machine learning and artificial intelligence, I'm very, very interested to get into that field. I am not in that field yet, but I'm very interested to see how that field can connect to what we are doing in light-matter interaction. It's very, very exciting.

Putting the Meta in Materials

ZIERLER: Nader, a term that is so closely associated with your career, I wonder if you can help me understand it, metamaterials. The term "meta" almost has a philosophical connotation to it. I wonder if that's relevant at all in your decision to name this metamaterials.

ENGHETA: No. It is not. By the way, I did not name it metamaterials. Someone else did. Before that, we used to call artificially engineered materials "complex media". Before that, they used to be called artificial dielectrics, etc. Let me tell you what metamaterials, i.e., engineered materials, are. As I mentioned a few minutes ago, in order to utilize waves to do interesting things, we need to control and manipulate waves. For that, of course, materials are needed. Now, there are usual materials in nature that we see around us: metal, glass, wood, you name it. These materials have usual properties when they interact with waves. But then can we have materials and structures that would have unusual, beyond the ordinary effects, on waves? That's what's called metamaterial. "Meta" in Greek means "beyond". These materials have beyond the ordinary properties. What are they? How do we make them?

Now, if you pick any regular, usual material from the periodic table, it consists of atoms. When you put them together, you have molecules and so on, and you have a collection of atoms and molecules, with their special patterned distribution. And those atoms and their patterned arrangements would provide special properties when electromagnetic waves interact with them. In metamaterial, we go beyond this arrangement to a new level of organizations. Imagine that you get tiny objects made of materials, and you embed them in another host material, with the proper arrangement you make. Now, with the proper designs and the proper choice of your tiny inclusions, and the choice of the host, and the specific geometry of each of these inclusions, you would be able to have composite structures that, when the wave interacts with them, behave in very unusual ways, in ways that each one of those constituent elements would not behave. But when you combine them, it will have that interesting property. Let me give you an example. Would it be possible to design a material, a metamaterial, that would have an effective index of refraction near zero? The answer is yes. We have done that. Is it possible, for example, to use materials that when you put them around some objects, it makes it less scattering? Yes, it is possible to control the wave around the objects. Is it possible to make a material with a proper design, such that when you send a wave through it, as the wave goes through it, it would solve equations? Yes, we have done that. You see that these types of structures, as you design them to manipulate the waves, have properties that would be beyond each of their individual constituents.

ZIERLER: Nader, just as a snapshot in time, what are you currently working on, and beyond your research group, what's more interesting to you in the field?

ENGHETA: Right now, we have several different research programs in my group. One of them is just this last point I mentioned. We are very interested, and we have done work, on design of materials that, when the wave interacts with them, behave as analog computing machines with waves. For example, we have introduced the idea and we have experimentally demonstrated that we can build a material with a very interesting geometry, such that when we send an electromagnetic wave through it, we have been able to solve integral equations with waves with the near speed of light. First, we did that in the microwave domain, just to do the proof of concept, and then later together with our collaborators we did it for the much shorter optical wavelength, visible and near IR. This research direction has a very interesting and exciting future we are looking into. Imagine that you would be able to have such nanoscale optical analog computing material structures that would also be programmable. That's one of the research directions we are working on right now. We've already shown a proof of concept that it is possible to solve equations and to do mathematical operations with waves in materials, with near speed of light. But now we say, "Now that we have shown this, what would be the next stage?" The next stage is to try to make it programmable, because if we can achieve programmability for these material nanostructures, if we can do reconfigurability, you can imagine what will happen next. Imagine that in future you would have optical material nanostructures that can do mathematical operations of your choice with the near speed of light. After you are done with your computation, you can basically "erase" that structure, and rewrite another nanoscale/microscale optical analog computing structures. Just like when we used to have rewriteable CDs, you remember, in our laptops, can we do that for nanoscale/microscale material-based computers to write on, let's say, disk and so on, that you would do mathematical operations with light? You could solve the equation you want, and then you erase it, and write another one. That's one of the research directions we are interested.

Another one of our research programs is what we call the four-dimensional metamaterials. Now, you may ask: what do we mean by that? We know that when a wave propagates through a medium, if you shape the medium, you can have interesting functionality, like the lens, or the example I mentioned. The glasses that you and I are wearing are basically the structures that have specific geometrical shape, and that's where we have lenses for example. Can we envision a material scenario such that as the wave goes through it, not only is the material a function of space but also a function of time? In other words, what would happen if you change the material properties in time as the wave is going through this? That's what we call it, four-dimensional metamaterials.

Not only could the material parameters be a function of space, but it could be also a function of time. That would allow you to have more control and higher degrees of freedom in controlling the waves. Let me give you one other current research program in my group, and that is the program which we have been developing over the past several years. We call it near-zero-index photonics. In a nutshell, if we can design a material in which the effective index of refraction would be near-zero, and we have done that, you can have fascinating properties in wave propagations. As a footnote, I have to say that this is one of those interesting research cases that started with a curiosity-driven question. Back in 2005, I asked this simple question to one of the members of my group. Imagine that you have two waveguides, and imagine you would like to connect them with an arbitrary connector shape. What if in the connector between the two waveguides we put a material with relative permittivity near zero? what would happen? It was purely a curiosity-driven question. At that time, I didn't have any application in mind, but that question turned out to lead us to a lot of interesting applications. What happens is this: without getting too much into the technical details of this phenomenon, which we called "supercoupling", when we have the index of refraction near zero, the wavelength of a wave is stretched.

When the index of refraction becomes smaller and smaller, the wavelength would be stretched more and more. When the wavelength is stretched, the phase distribution becomes uniform in this structure, which means that if I have two sources far apart, the two sources behave as though they're near each other. In that case, you can have quite a fascinating series of wave phenomena in such structures. Over the years, we have developed various different wave concepts that relate to this issue. This has opened up many interesting possibilities in wave-matter interaction, because it can offer a very interesting set of applications in various fields such as in thermal radiation management, in quantum engineering and quantum physics, particularly quantum optics. It really connects to a diverse set of fields. Just to finish my answer to your question about what other topics I would like to get into. I have already partially answered that question. I'm very interested to see how what we are doing in my group can contribute to the artificial intelligence and machine learning because, after all, in machine learning and artificial intelligence you need to do a lot of computations. Can the computing machine that we have introduced and have been working on contribute to that? My intuition tells me it will, but we'll see. If we can speed up the computing, that will be very helpful and impactful to everyone, as obviously each of us always deals with a lot of data in every moment in our lives.

ZIERLER: Nader, two questions as they relate to future developments in some very exciting technologies. Of course, I'm sure you've been following all of the excitement about room-temperature superconductivity, and it's purported achievement out of South Korea. Do you see your research as contributing to the broader quest of achieving room-temperature superconductivity or, conversely, would the achievement of room-temperature superconductivity be a game-changer for the kinds of things that you work on?

ENGHETA: That's a good question. As far as the first part you mentioned, at the moment, I don't see how my work can contribute to that. But as for the second part of your question, if such room-temperature superconductivity could be possible, without a doubt, it would clearly contribute a lot to every aspect of science and engineering that deals with waves. I'm very curious. Everybody's curious to see what happens to that claim. But, yes, it would have a major impact in many areas, including the areas of wave propagations. The other way around, in other words, whether what we do can contribute to that, at the moment I don't see that connection. But, clearly, the other way, the connection should be there.

ZIERLER: Now, it's the same question with a different advance, and that is quantum computation. Are you working to advance the achievement of a scalable quantum computer or, conversely, once scalable quantum computing is available, would that also be a game-changer for your research?

ENGHETA: I think in this case, my guess is both ways. I think the work we have been doing on near-zero-index photonics has an interesting connection to quantum phenomena. For example, as I mentioned before, in such near-zero-index platfroms two sources far apart can interact with each other as though they're in the near field of each other. That can relate to interesting aspects of quantum entanglements. This has the potential to contribute to quantum engineering. Conversely, I think, yes, any aspects of quantum computation can also help us, although what we are doing in my group is more on the wave physics, not necessarily quantum, but inevitably these two topics can be connected to each other.

A Special Caltech Honor

ZIERLER: Finally, Nader, before we go back and establish some personal narrative, the topic that brings us together, you were named a Distinguished Alumnus for Caltech this year. First, congratulations for that.

ENGHETA: Thank you so much, David. I'm very honored and humbled to be selected for this award. I want to say, in my wildest imagination, I could not have imagined to belong to the list of awardees, which include some of my scientific heroes, like, Professor Kip Thorne—

ZIERLER: [laugh]

ENGHETA: —with whom I had a course in gravitation when I was at Caltech.

ZIERLER: Nader, tell me what it was like when you received the news, who gave it to you and, more broadly, if it provided you an opportunity to reflect on what your Caltech education has meant for you.

ENGHETA: First of all, it was quite exciting, and I was really, really happy when I heard the news, and really felt humbled and honored, as I mentioned. I received an email from the President Rosenbaum of Caltech. As you mentioned, it brought back great memories of the years I spent at Caltech, because Caltech is a magical place, David. It has a special place in my heart. I learned a lot at Caltech, not only advanced topics in science and engineering but arguably more importantly I learned how to be a scientist. I learned the way of doing science. At Caltech, I learned how to think scientifically, to think creatively and critically. Caltech also taught me how to be courageous in going into new fields. I always think about this. It is amazing, those years I spent at Caltech taught me a lot about how to get into new fields, how to develop a new research domain, new research territories, how not to be afraid about going onto unbeaten paths. This great news that I received by email about the Distinguished Alumni Award first made me humbled and honored and, second it brought back good memories from those days.

ZIERLER: Nader, let's go back and establish some personal history, all the way back to the beginning. First, with your name, I know in Iranian culture, the Persian language, names have a rich meaning. Either your given name or your family name, what do they mean or what might they tell us about where your family comes from or what their ethnicity is?

ENGHETA: Let's start with my first name. My first name, Nader, is pronounced in Farsi as Nader; just like father. The literal meaning of that is "hard to find", "rare". But it's quite a common name. [laugh]

ZIERLER: [laugh]

ENGHETA: Linguistically, it's an Arabic word, but it's a common first name in Iran. It's interesting. I have to tell you an interesting story. When I came to the United States in 1978, the first few months whenever I was introducing myself, I was saying, "Nader Engheta." (I was pronouncing Nader, as it rhymes with "father".) I'm going to get to the last name too but, for now, I am talking about my first name. People said, "How do you spell it?" I said, "N-A-D-E-R.", and then they would say "Oh, you mean Nayder?"

ZIERLER: Yeah. [laugh]

ENGHETA: The reason they were saying that was Ralph Nader.

ZIERLER: Right.

ENGHETA: Because Ralph Nader, in those days, was a consumer advocate. There was a lot of—

ZIERLER: Unsafe at Any Speed!

ENGHETA: Exactly, that's exactly right. I came in 1978, so it was just a few years after he had Unsafe at Any Speed. Anyway, I was saying, "No, it is pronounced Nader (as in "father")." But they keep saying "Nayder". After six months, I gave up.

ZIERLER: [laugh]

ENGHETA: Then I said, "That's fine. Let's just call myself 'Nayder'."

ZIERLER: [laugh]

ENGHETA: My last name has a literal meaning which is "discontinuity". Linguistically, it's an Arabic word. It is an usual last name (with the meaning "discontinuity"). The story I've heard from my family members about the reason behind this choice as last name is this (I'm just telling you what I have heard. I don't know how accurate all the details are): Before 1935 generally there was no last name in Iran. Then in 1935, the government decided that everybody should have a last name, and so they asked everybody to go to this office, and choose a last name. My grandfather, the father of my father, whom I never met, by the way, because he passed away before I was born, went to this office and selected a last name. It wasn't this; it was something else. Then a few days later, he received a note stating that that last name was taken by somebody else, so he should choose another one. He chose another one. Again, apparently a few days later he went there and they said, "That one was also taken." Although I've never met my grandfather, but I've heard that he had a very short temper, so he was very upset. He said, "I've chosen my last name two times, and both times you said that those words were taken by someone else. I'm sick and tired of this. Why don't we discontinue this process? Why don't we just put it "discontinuity". They said, "Oh, nobody has chosen that last name." So Engheta (meaning "discontinuity") became our last name.

ZIERLER: [laugh]

ENGHETA: [laugh] That's the story, at least, this is what I've heard. Again, the accuracy of that I cannot guarantee, but that's just what I've heard from my family members.

Tehran and the Revolution

ZIERLER: Where is your family from?

ENGHETA: From Tehran. Both my parents were born in Tehran. I was born in Tehran, and I grew up there—I was born and raised there. I went to elementary school, high school, and undergraduate college, University of Tehran there. Then in the summer of 1978, I came to the United States to come to Caltech.

ZIERLER: What neighborhood did you grow up in, and what were your parents' politics?

ENGHETA: Remember, this was before the 1979 Revolution in Iran.

ZIERLER: Right, of course.

ENGHETA: The neighborhood I was born was called "Chaharrah Aziz Khan", later was known as "Hafez street". When I was around, I think, 6 years of age, we moved to another neighborhood, and that's where I started going to elementary school. That neighborhood was close to the Institute of Pasteur where they were doing studies on immunology and vaccination. That's why I have always been familiar with the name Louis Pasteur. He's one of my scientific heroes. I went to elementary school there, and then to high school, and then to the University of Tehran while we were living in the same place, the same house, until 1978, when I came to the United States. We were always in that neighborhood. Regarding the politics of my parents, in those days, just like now, nobody could talk that much about politics outside home, because obviously it was not a democratic regime. Regarding education, my mother particularly played a very important role, always telling us that the education is the most important thing. That was one of the things she always emphasized to all of us, all my brothers and sisters. We have a large family. We were four brothers and two sisters. Two of my brothers have passed away. I'm the youngest one, and my oldest brother who passed away two years ago was the oldest one. Then we have two other brothers and two sisters in between. I was the first member of my family who came—

ZIERLER: Oh, wow.

ENGHETA: —from Iran, and came to the United States. Then shortly after that, the Revolution happened.

ZIERLER: Was your family more secular or more religious, would you say?

ENGHETA: Secular. They were not religious at all. They were secular, and that's why after the revolution, they were unhappy with the way the revolution evolved into a very hard-liner religious government. Basically, many people were disappointed with what happened in that revolution and after that revolution, which moved towards the extreme religious idealogy.

ZIERLER: What were some of the most important holidays or customs in your family, growing up?

ENGHETA: Very good question. Of course, one of the most important holidays for Iranian families is the Persian New Year. The Persian New Year is a very joyous event for all family members. I don't know to what extent you are familiar with that holiday. It's basically the beginning of spring, and it's a secular holiday. It has nothing to do with any religion. It's always the beginning of spring, so approximately March 21st when the Persian new year starts. Particularly for children, that's a very, very joyous time. You go and visit family members, and pay respect to older family members. It's the beginning of spring, so in fact the nature also is rejuvenating at that time. That was one of the major holidays we have, and as children we were always looking forward to it, particularly after the wintertime.

ZIERLER: Nader, did you grow up with the sense of international affairs, things like the Cold War, the Arab-Israeli conflict?

ENGHETA: Yeah. That's an excellent question, because sometimes my daughter asked me that question—but please bear in mind that this was the time before we had internet, email, social media, etc. Access to the news internationally was not that easy in Iran then. We had some general sense of these international efforts that were going on, but not as much, until I came to the United States. Obviously here in the US, it's an open environment. So you can read newspapers, and so on and so forth. Yes, we had some knowledge of what was going on internationally, but not as much as later when I came to the US. Speaking of technology, that's one of the major differences between the past and now. In those days, particularly in a country that news was not necessarily accessible openly to everyone, we got the news only from TV or newspapers, and those of course were run by the government in those days. We had some knowledge of what was going on in the world, but not as much. Of course, nowadays because of internet access we can have much more access to the international news.

ZIERLER: Nader, tell me about the schools you went to growing up in Iran.

ENGHETA: For the elementary school, I went to a public school, a small public school, not too far from where I was living. Then for the high school, I went to a school that was one of the well-known high schools in Tehran then. In those days in Iran the elementary schools were for six years, and high schools were for six years. It was kind of like old French style in those days: six years of elementary school and six years of high school, and that was it. I went through that system, and it was a very rigorous education, as far as the mathematics, physics, and the sciences were concerned. In those days, after you passed the 9th grade, when you wanted to go to 10th, 11th, and 12th grades, you had to choose one of the three paths. If you were interested to go into science and technology, you would choose the path called the "mathematics path". If you wanted to go into fields like biologiocal fields such as medicine and so on, you would choose the path that was related to biology. (It was called "natural path", which by "natural" they meant things related to "biology' and "anatomy", etc.) If you wanted to go into law and literature and so on, you would choose the "literature path". Up to the 9th grade, all subjects were common for all students. After the 9th grade, you had these three paths that you were going to choose from, and that basically would determine where you want to go after high school. For example, if you want to go to science and engineering, obviously you go to the mathematics path, because it had more emphasis on some of those aspects.

That is what I chose and after high school I went to University of Tehran's school of engineering, the department of electrical engineering. Now, here is another interesting point. Sometimes people ask me, "You love science, but why did you go to an engineering school?" This is a good question. In those days in Iran, if you wanted to become a scientist, you would go into the engineering school, because engineering schools were the most challenging and difficult places to go. Basically, a lot of very rigorous science topics were taught there, all the mathematics, physics, engineering, and so on. In those days, there were also departments of physics and chemistry and so on. But traditionally in those days if you had gone, for example, to department of physics, you would've become a physics teacher in high school. But if you wanted to become a scientist, then the tradition in those days was to go to the school of engineering. Now, of course, the situation is different. You go to the physics department, you become a physicist, and so on. But in those days, the school of engineering was the place that you would go in order to become a scientist.

ZIERLER: Nader, was it also useful in the sense that going to a school of engineering would be a likely path to a good job in industry, as a safety option?

ENGHETA: Absolutely. Yes, that's very true. As I mentioned, it was a prestigious school to go to. If you went to the school of engineering at University of Tehran, or school of engineering at Sharif University—now it's called Sharif but in those days it was called Aryamehr University—those would be the places where you could become scientists, or you could have a very good job in industry. That was basically the gateway to your professional future.

ZIERLER: Nader, an overall question relating to your education. Did you grow up with an appreciation for the greatness of Persian science and engineering, of Iranian history in these areas?

ENGHETA: Yes. That was always an emphasis, and not only the Persian science but also the Persian literature. The Persian literature and the Persian poetry are part of our DNA, so to speak. I love the Persian poetry. I don't have any talent in writing Persian poetry, but I love to read it. The big names like Omar Khayyam, for example, like Ferdowsi, they were wonderful poets. Omar Khayyam was also a mathematician and scientist. That was something that was emphasized.

ZIERLER: Now, because engineering was the most difficult course of study, as you explained, was there a lot of physics built into the curriculum? Was it more like what we might call an engineering physics program here in the United States?

ENGHETA: That's right, yeah, exactly, and also engineering part. Not only was there a lot of courses in the science but also—we had engineering courses. You describe it nicely. In those days, it was like electrical and physical sciences.

ZIERLER: Being a college student before the revolution, leaving in 1978, did you feel change in the air? Did you feel something big was about to happen?

ENGHETA: Absolutely, clearly. It's interesting, in those days, the school of engineering at University of Tehran was also a hotbed of political activities. It turns out that I entered University of Tehran in 1973, I finished it in 1978, and the Revolution happened a few months later. We were the closest five years to the Revolution time. Yes, you could tell, particularly, I have to say around—if my memory serves me correctly—around May or June of 1978, you could tell something was going to happen. Even a few months earlier than that, you could see there were demonstrations in this street, that street, at the universities, the students strikes, all of those things were beginning to avalanch. I remember when I finished my last course in June 1978, and after that I was getting my bachelor's degree, then by the time I got my passport and related paperwork, got my ticket, visa and so on, it was around August 1978. Then things started to really accelerte. I remember the day I left Iran, August 31st, 1978. In fact, today is August 15, so in about 16 days from now, it will be 45 years since I left Iran.

ZIERLER: Nader, were you politically active as a student? Were you campaigning against what you saw was coming?

ENGHETA: No, I was not politically active, but all of us students have political knowledge, and we were also interested. But, no, I was not very active politically, but there were many friends and students who were active. But, in those days, all students were very interested in politics and we all were interested to see what would happen to the future of Iran. In August 1978, it was very hard to predict what would happen. I tell this to my daughter and young colleagues who ask:, "Could you predict that the Revolution would happen a few months later?" No, nobody could predict that. Everybody knew that something was going to happen. But what was going to happen and how rapidly it could happen was very unpredictable. If you had asked anybody in Iran in, say, March of 1978, "Do you think within one year, by February 1979, you would have a different government?" nobody could predict that, nobody, because Shah's government appeared to be so powerful then. Then within a few months, things started to collapse. It's just an unbelievable change that happened then. As I said, the rest is history. As I mentioned, in 16 days, it will be 45 years since I left Iran.

ZIERLER: Nader, it's interesting because even if the revolution never would've happened, it was common practice, of course, very talented students would go abroad for their graduate school. It begs the question for you, were you looking specifically to go internationally because the domestic situation was so troubling, or you would've left anyway?

ENGHETA: I would've left anyway. In fact, at the time that I started applying to Caltech, there was no sign of revolution or anything. My plan was to come to the United States, and have my higher education here. It so happened that after I applied and got admission, things started to happen. Independent of whether the Revolution would have happened or not, I was coming to the US.

Pasadena Passage

ZIERLER: Here's the question I've been waiting to ask. How did you hear about this little school called Caltech in Pasadena, California? [laugh]

ENGHETA: Excellent question. Wonderful question. Before I answer that, I have to preamble it by saying that in those days when we were applying for universities, particularly from some country far away, there was no internet. There was no email. How did we apply? That's an interesting question.

ZIERLER: [laugh] Right.

ENGHETA: The way we were applying was by just writing a letter longhand, literally, to ask for application forms. As a result, you have to start earlier. I will tell you how I came across the name of Caltech. But first let me tell you how I applied. I wrote a letter to Caltech and asked "Could you please send me the application form?" Now, how did I hear about Caltech? As I said we had to start one year earlier to apply and to start the process. When I was considering coming to the United States for my higher education, I heard from another friend, who was one year more senior to me, who said, "Have you considered applying to Caltech?" I said, "Tell me about it. Where's Caltech?" He said: "This is a fantastic place. It's a place that is very unique with a wonderful atmosphere for fundamental research in science and engineering." I said: "This is very interesting. Tell me about it more." He said: "This is the address. You can write to them, and ask for a catalog." Remember, again, there was no online system that we could go and get the information online. So I wrote to Caltech, and asked for the catalog. Oh, one thing I want to mention, this friend told me that if you want to ask for a catalog, you have to pay for it and to send some fee—I don't know—$9, $10, whatever. I went and I got the money order from the bank, and then I put it in an envelope and mailed it to Caltech. After two, three weeks—I don't remember how long it took—I got a package from Caltech with the Caltech catalog, and they sent the money order back. To me, that was so amazing that they were so honest that they didn't even cash that check. They sent it back. They said: "We don't need the money order. This is a catalog. It's free. You can have it." I started going through the catalog, and I was so fascinated to see names of the professors there, many of them were Nobel Laureates, and some of Laureates among the alumni.

I became fascinated. I said to myself: "This is a great place. I should apply." I wrote another letter. This time I asked: "Could you please send me the application form?" I don't know how the admission process works at Caltech these days now, but in those days first they sent a pre-application. I remember they asked: "Fill out this form and send it to us to see whether or not we can send you the application." I did that. I had good grades. I ranked number one among the graduates of the school of engineering of the University of Tehran in that year that I graduated. After I sent Caltech the completed pre-application, Caltech sent me the full application form. Then I filled out the full application form. There was no typing. Literally, I filled out the form by writing with hand, and sent it to Caltech. Then I remember the day—and this is one of the best days in my life—I remember the day that I received the admission from Caltech. It was April 1st, 1978, April Fool's Day.

ZIERLER: [laugh]

ENGHETA: [laugh] It's interesting you asked me about the personal history. I told you about the Persian New Year, Iranian New Year. Iranian New Year is March 21st, as I mentioned. The tradition in New Year is for almost two weeks, the schools are closed. People have holidays for almost like two weeks. At the end of the two weeks, there's a special day in the Iranian culture when people go to picnic. This is at the end of the two weeks of New Year celebration. With the family, you go to the outskirts of the city for a picnic. That day in 1978, I was with my sister, her husband, my mother and father, and some other family members. We went to this picnic area. At the end of the day, I was going to my sister's house to stay over, and then next day, I was going to go back to my home. Next day, my mother called me. She says, "You have a package that arrived." I asked, "It's from where?" My mother could not read English. Anyway, I found out it was from California Institute of Technology. So I asked my mother: "Tell me this. Is it really very light or is it heavy?"

ZIERLER: [laugh]

ENGHETA: She said, "I don't know. Come over and then you can see it for yourself." I went home, and I opened the package, and it was the admission. That day really changed my life—

ZIERLER: Wow.

ENGHETA: —truly.

ZIERLER: Nader, I have to ask, did you know at the University of Tehran, did you ever cross paths with Mory Gharib, or did you meet him at Caltech?

ENGHETA: Mory Gharib is a very good friend of mine, and we met at Caltech, and we studied together. Yes, Mory is a great friend. I know he's there, and I look forward to seeing him when I come to Caltech for the alumni award in October.

ZIERLER: But you did not know him at college in Tehran?

ENGHETA: No, I did not know him there. Later when I met him at Caltech, we became very good friends, then he told me that he also graduated from the same college but I didn't know him there. It's very interesting you mention about Mory. When I came to Caltech, the first day I came to campus, I went to the Office of International Students, to start the paperwork. The person who was in charge of the international students said: "I'm going to call someone to come and talk to you." She called Mory Gharib, and Mory came. He has been such a wonderful friend. He was at Caltech, I think, a year before me. He was very kind, and he came, and he helped me settle and so on. He became a very good friend. He was in the aeronautics department, I was in electrical engineering, and we studied together, getting ready for the PhD qualifying exam. It was wonderful.

ZIERLER: Nader, I must ask, when you left Iran, did you leave with a feeling that you might not be able to go back home perhaps ever again?

ENGHETA: Yes, that feeling was there. Of course, no one could predict the future. But I came, as I mentioned, in 1978, and I haven't been back to Iran since then.

ZIERLER: To this day?

ENGHETA: I'm sorry?

ZIERLER: To this day, you haven't been back?

ENGHETA: That's right, to this day, I have not been back. Often people ask me, "Why you haven't been back to visit?" The reason is not political. You can ask Mory exactly the same question, and most likely he will give you a similar answer. The reason is that for people our age, when we came from Iran, for the reason I'm going to explain, there was no opportunity to go back. I tell you why. I came to the United States in the summer of 1978, and in those days international students, just like now, would say: "Maybe the following summer I would go and visit my parents for a couple of weeks." In those days, we were saying to ourselves, "Maybe next summer I will go and visit my parents." But by next summer, the Revolution had happened in February 1979. When the Revolution happened in 1979, of course, everything was obviously in turmoil in that country, so it was not possible to travel during that turmoil. I said to myself: "No problem. We wait until maybe the following summer we go and visit our parents." But by the following summer, if you recall, the hostage crisis had happened in Iran in November 1979.

Because of the hostage crisis in Iran, issuing a student visa for Iranian students stopped. If we had left the United States to go and visit our parents, we could not have been able to come back because we could not get a new visa. We said to ourselves: "Right now we're in the middle of our PhD program, so we cannot leave the country to go and visit our parents. We wait until hopefully the following summer, we would be able to go and visit our parents. Hopefully, the hostage crisis will be over by then, and the visas will be issued again." But by the following summer, the Iran-Iraq War had started, and we hadn't done our military service. If we had gone back to visit our parents, we would have been taken to the military service. We said to ourselves: "We don't want to travel there now." That war lasted eight years. By the time that war ended, it had been 10 years since I came from Iran. My brothers and sister, one-by-one, got out of Iran. The country became completely different from what I remembered then. Then one thing led to another, and so on, and I haven't been back for 45 years. I'm sure if you ask Mory, most likely he has a similar reason.

ZIERLER: Nader, coming to the United States, coming to California, how was your English at that point?

ENGHETA: When I was growing up in Iran, of course, the official language was, and still is, Farsi. Now it's different, but in those days everything was in Farsi. In high school, we had a course in English, but it wasn't enough. It was just like a couple of hours per week. Before I was coming to the United States, when I decided I was going to come to the United States for higher education, I started learning English in classes at night. My English, from the points of view of grammar, writing, and reading, was OK. But from the point of view of speaking, of course, I was OK, but I needed to be in an environment to improve. We had some speaking ability in English, more so on the writing and reading, but listening and talking was less. When I came to the United States, the first few weeks, of course, were very hard. Even speaking and listening in English I was familiar with were obviously different; different accents, different expressions, etc. The first few months were a very interesting period when I was getting familiar with the English speaking here. I have to tell you this point. I don't know whether you have ever lived in a country with a different language.

It's a very interesting feeling, because all the times you have to focus on every word a person is saying. I remember I was telling myself: "Would there come a day when I am listening to somebody speaking English, I would understand it very easily without having to focus on every word that person is saying?" That day came about four or five months after I came to US. Being in the environment is the most useful thing. You can learn the language very nicely. I'm talking about the speaking and listening in a language, i.e., the spoken part of it. Reading and writing were fine. We were good on that. That helped a great deal because I was basically by myself. I didn't have any family member with me, so I learned it out of necessity. The number of Iranian students at Caltech were very few in those days. Mory Gharib was one of them. There was another Iranian student in electrical engineering, and there was one in civil engineering, another one in aeronautics, and one in physics. I think we were six Iranian graduate students at that time, and I think also five or six Iranian undergraduate students. We were so busy that we didn't have time to see each other. As a result, we were encouraged to learn the language very rapidly.

ZIERLER: What program were you admitted to at Caltech?

ENGHETA: I was admitted to electrical engineering. I was in electrical engineering but, as I mentioned, because I was very interested in physics, I also took several courses in the physics department. My PhD major was in electrical engineering, and I got a minor in physics too. As I mentioned to you, I took a course with Professor Kip Thorne in gravitational physics, and that was fantastic. I remember, in those days, we were saying: "this professor is so bright that one day he will win the Nobel Prize", and he did.

ZIERLER: One day. [laugh]

ENGHETA: [laugh]

ZIERLER: Nader, coming from the University of Tehran, did you feel well-prepared for your study at Caltech?

ENGHETA: Yes, I felt prepared quite well. We were prepared, we were ready, and it was a good match.

ZIERLER: Who became your thesis advisor?

ENGHETA: Professor Charles Papas. He passed away in 2007. He was a wonderful, wonderful man. He was an amazing person. He was one of the reasons I became very interested in electromagnetics. How did I get interested in electromagnetics when I was in Iran? As a child in Iran, I was always interested in finding out how things work. One day when I was in high school, one of my older brothers, Iradj, was working on a battery-operated transistor radio. He's very good with his hands and he is very knowledgeable about electronic devices. He lives in Germany now, in Hamburg. I was looking over his shoulder to see this transistor radio, and I asked him, "How does this gadget work without being connected to anything? It's not connected to a wall and so on, and yet I can hear music coming out of it. Where does that come from?" He said, "There is this special wave that connects the radio station to this gadget, and then the signal gets into this gadget, and then it is processed and, eventually, an acoustic signal is coming out."

I was instantly fascinated. I asked myself: "What kind of wave is that, how come I don't see it, and so on." That fascination and curiosity really propelled me into the lifelong journey to pursue this field. I decided to come to Caltech, because Caltech is one of the wonderful places in research in electrodynamics. Now, when I came to Caltech, I looked for Professor Papas, because I knew his book on this topic. The first quarter I was at Caltech, one of the courses I took was by Professor Charles Papas. I was very curious to see him, to meet him. Then finally, when I met him, he was a wonderful, wonderful, gentle person, very, very nice. He was very curious. He asked me, "Where are you from? What country are you from? When did you get here?" Then a few weeks later, I asked him, "Can I become part of your group and work with you?" He said, "Sure." I became part of his group around December 1978. Then two months after that, in February 1979 the Revolution happened. Then, of course, people would see in the news that the country Iran has the Revolution. One day, Professor Papas came to see me in the office. I was in the office where his graduate students were sitting. He said: "I'd like to talk to you. Come to my office." I went to his office. He said: "I know that you are very worried about your parents, because right now your country is going through this turmoil, far away." David, then he told me something that I will never forget for the rest of my life. What he said showed his caring personality and his humanity, and how he was caring for his students. He said, "I know that you're worried about your parents. I know you're lonely here. You came all the way here from your country far away. But I tell you this. Consider my family as your family, and consider me as your father. As long as I'm alive, I will take care of you. You're not alone. You are here with us."

That statement always stayed with me. He was indeed true to his words, and indeed he always supported me. Even to the point that when I became a full professor at University of Pennsylvania, and being considered for the endowed chair, he was always supportive all the way until his passing. Not only did I learn from him the science of electrodynamics, but I also learned from him how to be a mentor, how to be an effective educator. He was a fantastic mentor, and he was kind to all his students. I have many friends among his former students who speak very, very highly of him. He was really a brilliant scientist, a wonderful human being, and a great mentor. I always remember.

A True Expression of Community

ZIERLER: Reading the news reports, seeing what was going on in Iran on television, were you able to communicate with your family? Were you worried about their safety?

ENGHETA: Yeah, I was worried about my family. There were periods of time when you could not communicate. Telephone lines were not working. Again, please remember that these were the days when there was no internet and email, so the only way we could normally communicate was either through letters you wrote longhand, or the telephone. The telephone was very expensive in those days, very different from now that we can call anywhere in the world free of charge. [laugh] But in those days, telephones were very expensive, and we couldn't afford it, except once in a while. Those also were cut. It was for a period of time that my parents didn't know how I was doing, and I didn't know how they were doing back there. As I mentioned, this was the time that Professor Papas mentioned to me that "don't worry, you're not alone. My family is like your family, and this place is here to help you." Indeed, all of us felt so much at home at Caltech, even though our families had a challenging time far away in another country. If you talk to Mory Gharib, he will likely tell you a similar statement. Caltech was very, very kind to us, and I always remember how supportive Caletch was towards us. As I mentioned, Caltech is a magical place, and I always have fond memories of those days.

Charles Elachi and Interfacial Antennae

ZIERLER: Tell me about developing your thesis topic.

ENGHETA: What happens is when I joined Professor Papas's group, his research area was electromagnetic theory. I was very interested in electromagnetics, and so I started learning from him. The first project he proposed to me was quite fascinating. In fact, also now when I look back, I see it was like a curiosity-driven question as well. I learned the philosophy of scientific thinking from him. He taught me about the Doppler effect in physics of waves. He said: "We know what the Doppler effect is. But I have a question. What would happen if we are in the near zone of an antenna? What kind of Doppler effect do we have there?" This was a fascinating question. Even now, when I think about it, it was fascinating to search for an answer to that question. He said: "If you're interested, let's work on this. Let's see what interesting phenomena would happen in the near zone of an antenna." That encouraged me a lot to get deeper and deeper into wave physics to find out what was going on in the Doppler effect, what would happen in the near zone of an antenna, how an antenna works, and so on. I learned about that, and that led to my first publication in 1980, which was coauthored by Professoe Papas, me, and another postdoc, Alan Mickelson, who was one of his former students who is now a professor at University of Colorado Boulder. He was a great person. That was my first paper. Then Professor Papas had a grant from the Jet Proportion Laboratory on studying some of the aspects of remote sensing. He said: "If you're interested, we can work on the remote sensing aspect of this project." I became very interested in electromagnetic scattering from geological surfaces, and this was in collaboration with JPL. Just to show you how small the world is, the person whom I collaborated with at JPL while I was working on that project with Professor Papas was Dr. Charles Elachi. Does that name ring a bell? I'm sure you know who he is.

ZIERLER: Of course, Charles Elachi! [laugh]

ENGHETA: [laugh] He is one of the 2021 Caltech Distinguished Alumni Awardees.

ZIERLER: That's right.

ENGHETA: Charles is another fantastic person. He is a good friend, and he has always been very nice to me. We started collaborating with Charles Elachi, and Professor Charles Papas as my advisor, and myself. I used to go to see Charles to have scientific discussions. We published some papers together with Charles. You may know this, but Charles was also a PhD student of Professor Charles Papas'.

ZIERLER: Yes.

ENGHETA: Yes, from the same group but several years before me. When I entered Caltech, Charles had already graduated several years before. Yes, it's a small world, and so I started working on that project. I got into the field of electromagnetics and remote sensing, and then that evolved into my PhD dissertation on interfacial antennas. Now, what is an interfacial antenna? They are antennas at the interface between two media. This topic came from our work on remote sensing, because one way to model scattering from rough surfaces is to model them as local scatterers as antennas. For that, we needed to know how antennas radiate at the interface, and this was part of the theoretical dissertation I did.

Professor Papas was a theorist. That work had a very interesting impact on one of the technologies those days called monolithic microwave integrated circuit, the MMIC. At that time, that was a hot topic for microwave devices integrated all on the same platform, including filters, antennas, and so on. We needed to know how an antenna radiates when you put it on such interface and platfirm. Now, as I was working on those research projects, I was also interested in the fundamental aspects of physics. I was taking some physics course such as gravitational physics, electrodynamics, etc. Towards the end of my PhD study, I got interested in another work that Professor Papas had done with one of his former students on chiral media, which have special handedness, such as molecular structures with the helical shape. I got interested in that field. Then after I got my PhD from Caltech, I stayed one more year as a postdoc in Professor Papas's group, just to finish some papers. Then I started working in a company in Santa Monica, California. That company doesn't exist now, but in those days it was called Kaman Sciences Corporation, Dikewood Division. This was a branch of another company in Albuquerque, New Mexico. But this was a small branch in Santa Monica in those days, where most of the scientists there were Caltech graduates, and some of them were graduated from Professor Papas' group. I started working in that company in June 1983. While I was there, I continued my interaction with Professor Papas, finishing some papers, and so on. That company, as I said, doesn't exist now, but in those days, we were working on electromagnetic pulse interaction with materials. That's where I got interested in electronics, and I got interested in a combination of electromagnetics with electronics and with materials. While I was finishing up some papers with Professor Papas, I became more interested in chiral media, and we published a paper together with Professor Papas and one of his students in 1986. In 1987, I came to the University of Pennsylvania and started my faculty job at UPenn. In 1986 I got married. By the way, we got married in The Athenaeum.

ZIERLER: Oh, the best place.

ENGHETA: [laugh] Indeed the best place. That was really the best place. My wife and I always have a great memory of The Athenaeum. One year after I got married, I got an offer from the University of Pennsylvania, so we moved eastward. We drove cross-country. We didn't have any children at that time. Our children were born in Philadelphia. We drove cross-country, and I started my career at University of Pennsylvania 36 years ago.

ZIERLER: Wow.

Chirality and Electromagnetism

ENGHETA: I started my research group working on chiral media, I was so fascinated in electromagnetics of chiral media, which in a away was the precursor to metamaterials.

ZIERLER: In what way?

ENGHETA: In what way? That's an excellent question. One of the interesting aspects of metamaterial is to make structures that may not be naturally available, but you can make and synthesize them in order to do interesting things. Another aspect of metamaterials is to make a material in a certain wavelength regime with the properties similar to those of other materials but in different wavelength regimes. For example, if you consider the visible light, there are naturally available materials that have chiral properties. Many organic molecules with helical geometry have chiral properties. When you shine light on some of these organic chiral materials, the plane of polarization of light rotates as it goes through the material. This is something that was known in the 19th century based on the work of Arago and Biot, and inspired by Louis Pasteur in chemistry. But what we were interested to see was that whether we could achieve the same chiral behavior in the microwave regime. But in the microwave domain, there is no naturally available chiral materials that can exhibit such properties.

So one had to design and engineer materials that could imitate the chiral properties in the microwave region. I started exploring this research directions when I started my research group at the University of Pennsylvania. We were looking at metallic helices that could imitate the helical molecules but much bigger in order to make them suitable for microwave. We could show that in microwave we have very interesting properties similar to what nature has given us in the visible light. But now you could make it in microwave. In a sense, that was a precursor of making a material that has interesting properties not available naturally in the wavelength regime of interest. One thing led to another, and I expanded my research group to look at some of the applications of such microwave chiral material. Then an interesting thing happen: As you know, in science sometimes serendipitously you may get into a field that you didn't predict you would get into. Serendipity has happened to me several times during my research career so far. Here is one of them: In early 1990s, I was a young associate professor at UPenn. One day in my office I got a phone call from a professor in department of psychology at the University of Pennsylvania. His name is Professor Edward Pugh. I didn't know him at that time personally, but I'd heard his name, and he was more senior to me. He said he was referred to me as someone in the area of optics and electromagnetics, and he has some questions about optical fibers. He says, "Can we get together?" I said, "Sure."

I was puzzled for two reasons: one, why somebody in the department of psychology is interested in optical fibers; and two, he is a very senior, well-known professor, and I was just a new associate professor in a totally different field. How come he's interested in talking with me? Anyway, we made an appointment, and I went to his office, and he showed me a very interesting picture he had taken through the optical microscope of a cross-section of the retina of a class of fish known as green sunfish. He showed me that picture. He said he had some interesting optical questions about this picture. he said there was some hypothesis that this fish could see polarization of light. He had a hypothesis about the way this fish might see polarization of light due to their photoreceptor cells, the special double-cone photoreceptor cells this fish has. He said those photoreceptor cells look like optical fibers, so he wanted to talk to me about the optical fibers. I was fascinated by the fact that in nature there might be some animal species that can see polarization of light. As I said, I had come from the antennas, microwave, and remote sensing communities. And, of course in those fields, we knew that the polarization of electromagnetic waves is a very important characteristic of light. But I didn't know that in nature there were some animal species that could see polarization of light. Ed Pugh told me that, yes, there is a whole body of knowledge in a subfield of biology called polarization vision, and there are many classes of invertebrates, like bees, ants, octopus, squids that can see polarization of light. I was fascinated instantly by what he said. I said, "This is fantastic. I didn't know that in nature these species can see the light polarization." He said, "Yes, they see that. If you are interested, we can collaborate together," Ed Pugh is expert in color vision, neuroscience and visual systems, and he said, "Your area is electromagnetics and optics, so we can join forces, and we can try to understand how the species can see polarization of light, and what can we do with it." I said: "Fine, let's do it."

Again, as a side note, I'd like to add here that this is one of the scientific characteristics I learned from Caltech, that you don't need to be afraid to go into a new field. Go into the new field, and learn about it, and see what we can do. That's exactly what I did. I started collaborating with Ed Pugh, and we wrote a joint proposal. He was the PI, I was the Co-PI, we sent it to NIH, and he got the funding to start studying the photoreceptors of this fish. I was studying some of the electromagnetic and optical theoretical aspects of waveguiding through this photoreceptors. As we were doing this collaboration together, I said, "Ed, I have another thought about this topic. Yes, we are trying to study how they would see the polarization. But another question may be: Why do they see like this? Why have they been evolved through the evolution to have such ability?" That got us into another very interesting research direction. The question of why do they do it? He told me that zoologists and biologists have known for many years, since 1950s, that many of these invertebrates can see polarization of light. For some of them, they know why they do it, for example bees use polarization of the sky for navigation. I said, "Ed, let's do this. Let's try to understand if we can learn or get inspiration from the nature and whether we can apply that to physical devices. In other words, can we make a camera that can see the world as these species do?" He said, "That's a very interesting idea. Let's do that." Then we wrote another proposal. This time, I was the PI, and he was the Co-PI, and we submitted that proposal to get funding to study such bio-inspired imaging system. Can we make a polarization camera system inspired by the nature? That led us to an interesting research direction, and we developed a new research field, which we called bio-inspired polarization imaging.

ZIERLER: Right. Nader, was the field of biomimicry or bio-inspired research, were you part of that from the very beginning, or was that already in operation at that point?

ENGHETA: There were some already in operation in some aspects, but our input came from the aspects of polarization vision. There were other bio-inspired research directions, as you mentioned. But we came from the direction of bio-inspired polarization imaging. That was an additional degree of freedom we got inspired from what nature has done in this regard. We were very excited. While I was continuing the work on complex media and chiral media and so on, I expanded my group to explore this bio-inspired polarization imaging as well, in collaboration with Ed Pugh. That collaboration led to quite a fascinating direction. We have several patents on this topic.

I mentioned to you about the start-up company which was formed by other people based on the patents we had on these aspects of polarization imaging. That led to other interesting things. For example, we came out with a new idea how to detect a latent fingerprint using the polarization camera, non-invasively without touching the fingerprint. That led to other interesting research topics we did, like through-wall microwave imaging. We applied that technique in the microwave regime to explore how we can see through the walls to image the other side of the wall using the concept of bio-inspired polarization imaging. Again, to come full circle, I learned from Caltech how to be courageous to go into another field. I'm very much indebted to that sense of curiosity I learned from Caltech. The work I was doing in the microwave aspects of chirality, plus the work I was doing on the visible light for bio-inspired imaging, led me to my idea of bringing these two together, and try to go towards the physics and engineering of complex materials in the visible domain. That led me to conduct research in nanophotonics and nanoscale optics. That took me into an interesting path to combine my interests in materials science and my interests in optics, and bring these together. So starting from the microwave community and then moving into the optics, nanophotonics and nanoscale optics. That led me to other areas of my research, i.e., the near-zero-index optics, the concept of cloaking, optical nanocircuitries and modularized photonics, which was the precursor to what we are doing now as the metamaterial photonic processing and computing, to use materials as analog computing machines. These started with the idea I introduced in 2005 on the optical nanocircuitries.

ZIERLER: Now, Nader, I want to get to the near-zero index, but before we leave microwave chirality, just so I understand, do you mean chirality in the sense of handedness—

ENGHETA: Yes, Exactly.

ZIERLER: —that there's a left-handedness and a right-handedness to microwaves?

ENGHETA: Exactly. That's exactly right. Just to shed light on this, yes, if you get a helix, obviously helix is chiral because there's a right-handed helix and a left-handed helix. If you collect many of these right-handed helices, and you put them randomly oriented in a medium, and you send a microwave signal through this, you're going to see that the plane of polarization of this microwave signal turns to either right or left, depending on the handedness of those elements. These metamaterials consist of many elements, even though they're randomly oriented but the handedness is preserved. You can have the signature of handedness, which is a geometric concept, into the rotation of the microwave signal. That introduced quite a series of applications for us when we did that. Again, this was inspired by what the visible light in chirality was done in the 19th century by the work of Biot and Arago and Louis Pasteur. But we did it in the microwave, and that opened up an interesting set of possibilities because in the microwave, you can make these man-made helices. Then what happened is that when we went into visible, we brought this concept and what we learned from it in microwave, back to the visible domain to construct nanostructures with very interesting properties.

Wave Propagation and Getting to Zero

ZIERLER: Now, the term "near-zero index," is there something aspirational about that? Are you trying to get completely to zero, or what does that refer to?

ENGHETA: Yes, it is. Let me take you back a little bit just to explain what we are referring to. A refractive index is one of the useful parameters in wave propagation in media. Refractive index determines the relation between the frequency and the wavelength, which of course relates also to phase velocity of wave in the medium. If you go from one medium to another medium with different refractive indices, the wavelength would be different in two media, even though the frequency is the same in both media. When you have a material you design specifically to have a refractive index near zero—it doesn't have to be exactly zero, it can be near zero -- the wavelength would be stretched in that medium. You might ask: "So what? OK, the wavelength is stretched. What good does it do?" In order to address that question, let me step back, and tell you the general concept here. When you have a wave illuminating an object, the way the wave scatters depends on many factors, one of which is the size of the object. But when we say the size of the object, size compared to what? Compared to the wavelength. The yardstick is the wavelength. If you have a wavelength that's 500 nanometers, like wavelengths of light in middle of the visible spectrum, if you hit a particle that is 250 nanometers in diameter, that's half a wavelength, and that causes large scattering. If you have a microwave that has a wavelength of, let's say, 20 centimeters, when you hit an object that's 10 centimeters in diameter, that's half a wavelength too, and the scattering of this object is also similar to the other 250-nm particle. Everything is with respect to the wavelengths in order to get the yardstick in our comparison of the size.

What does that mean then when I make a material in which the wavelength is stretched? If the wavelength is stretched, that means when you put an object inside this medium, that object would look small compared to the wavelength in that material. Let's say originally you had your wavelength 10 centimeters, and your object was 5 centimeters. That's half a wavelength. It has certain scattering properties. Now imagine you use the same signal, but you bring it into the medium in which the wavelength is stretched by a factor of three. In that case, the wavelength in that material is 30 centimeters, but your object is still 5 centimeters. If you put that object into this material, now the object is one sixth of that wavelength. The scattering would change, even though the size of the object is still the same, and even though the frequency of your wave is still the same. But because the medium has changed, and the wavelength has stretched, the size of the object looks smaller to the local wavelength.

To continue this line of reasoning, what would happen if you brought the index near zero? That means the wavelength becomes longer and longer and longer, even though the frequency is the same. That means the object looks smaller and smaller to the local wavelength, even though you haven't changed the size of the object. It still is five centimeters. What does that mean? That means scattering will change a lot, even though your frequency is the same, even though the size of the object is the same, if only you're changing the material. You see fascinating features in such media. It means what? It means you can have a scenario that when you put an object inside the structure, it may not scatter. For the observer sitting outside, the observer would not know that the object is there. Essentially, you have cloaked the object. If you put an object outside, you send the wave through the scatters, so the object can be seen. But if you put this object within this material, or you put the material around it, the object become less visible.

ZIERLER: Nader, to clarify, this is experimentally verified or this is a theoretical concept?

ENGHETA: It's experimentally verified. Yes, we did that. But, of course, it depends on the specific frequency, obviously. Remember, at the beginning of our discussion, I told you about two waveguides connected with a certain connector? There, if we use the near-zero index material for the connector, which connects this waveguide and that waveguide, even though the waveguides are far apart, from the electromagnetic point of view they function as though they are sitting next to each other. The wave coming from this waveguide tunnels through this near-zero-index channel from one side to the other. As a result, if you put two sources in such media, even though they may be far apart, they behave as though they're near each other.

The implication of this phenomenon is very important because what that means is that you can have a body with a given size that would look like a point. When I give talks on this topic, I always tell the audience, from the electromagnetic view point, the near-zero-index media may look like a point. The object in such media looks much smaller than it really is, even though it's not small, but it looks smaller than it is, when compared to the local wavelength. In other words, instead of reducing the size of the object, you're increasing the wavelength in the medium. Rather than making the objects small in order to reduce scattering, you make media in which the wavelength is stretched, and the effect is effectively similar. This has interesting implications in quantum optics, in thermal management, so on and so forth. To give you an idea, if I have a hot object, its thermal radiation is incoherent. At every point inside this object, the local current oscillates independent of the current at another point. But if this material is the near-zero-index material, or epsilon-near-zero—we call it—ENZ material, for those ENZ frequencies, the wavelength is stretched, and consequently the oscillating current here and oscillating current there are somewhat partially correlated. As a result, the thermal radiation becomes spatially partially coherent and as a result it becomes more directed. So you can bend the object, which causes the thermal radiation to have a different pattern. Another interesting aspect of near-zero-index materials is in flexible photonics. Imagine you have an optical platform with a given set of optical properties. For example, imagine cavity resonantors with specific resonance frequencies.

It is known that when the shape of this platform changes, its optical properties do change. For example, when you change the shape of a conventional cavity, its resonance frequency may change. But when you have ENZ materials in such cavities, their resonance frequency does not change when you change the shape of the cavity. We did an experiment in my lab , with three different cavities. We designed three different cavities with very different shapes, and we sent the signal to each one of them. Exactly at the frequency for which these cavities behave as near-zero index structure, the transmission signals coming out of these three cavities are the same, even though the three cavities look very different. We have been very excited about this concept. We introduced the concept of ENZ-based super coupling in 2005. Our paper on this topic came out in 2006 in PRL, Physical Review Letters, and it's one of the highest cited papers that I've had since then.

Invisibility and Real Science

ZIERLER: Nader, how much confusion was there or over-excitement that this would lead to invisibility kinds of things?

ENGHETA: It's interesting because [laugh] there was a lot of excitement at that time. We were saying, "Please note that we are not saying that you can be invisible yourself." No. The body is, of course, very complex. We were talking about the objects that were small compared to the wavelength of wave. But, yes, there was excitement at that time, but we were very clear about the limitations of our approach. It's only for a specific wavelength that we have, and for specific sizes. Of course, cloaking is one aspect of that. But the more impactful aspects are in the photonic side, in other words how we can have a system that should be flexible in space without changing its optical properties, how we can have a system in which you have the possibility of coupling among the sources even though they're not near each other with possible interaction and implication in the quantum engineering, and also its thermal aspect which I discussed earlier.

Another area of my research is the optical nanocircuitries. That's the area which resulted from the fact that I'm both a physicist and an electrical engineer. That's a topic that connects these two fields together. In electrical engineering and electronics, we deal with lumped circuit elements. The circuit course is one of the first courses we teach to our undergraduates in electrical engineering. In circuits, we have lumped circuit elements such as the capacitor, the inductor, the resistors, etc. I call these elements the alphabets of electrical engineering. We know each one of them, and we know how each one of them functions. When you connect them together, we know what would happen. That is why I call them the alphabet, because in alphabets you have a certain number of units, and then you can connect them in so many different ways, and you obtain sentences, paragraphs, and so on and so forth. In electrical engineering, we have these circuit elements, which we call lumped circuit elements. It has been known for many decades. The question that was always in the back of my mind was this: Why is it that in electrical and electronic engineering, we have lumped circuit elements, but in optics we didn't have such a things at that time? Why is that? The thing that was puzzling me is that both of these fields, whether we are talking about electrical circuits or we're talking about optics, effectively both of them follow Maxwell's equations. They follow the same laws of nature, but they were developed in two different communities. In electrical engineering community, we have lumped circuit elements in electrical systems. If you look inside your iPhone, you can see those things there. But in optics community, traditionally we were talking about lenses, waveguides, mirrors, and so on. How come we didn't have a lumped circuit element in optics? This question was in the back of my mind for years, and I was trying to see whether it would be possible to unite these two fields. Can we bring these two fields together? After I started my research in the electromagnetic wave interaction with materials, then several years later in 2005, I came up with this idea proposing nanostructures, designed with proper materials and proper shapes, behaving as lumped circuit elements with light. We decided to study this. Let us assume I have one nanoparticle, say, a spherical nanoparticle.

The shape shouldn't matter that much for, so let's say a sphere because we could calculate it more easily and analytically. When I had a spherical particle, and when this particle is made of a dielectric, say, glass, what would happen if we illuminate this with a laser beam? It scatters. Then we did the analysis, and we found out that when I looked at the field distribution inside this particle and did the analysis, I would get an equivalent of a lumped capacitor. We know what happens in capacitors in electrical system. You have a capacitor, you put a voltage across that you have a current, and there's a relation between the current and voltage of a capacitor. In optics, when I get such a nanoparticle, and when I illuminate it with a laser beam, I also have some electric field and some magnetic field in and around it. We calculated these fields, and we found out that the relationship between them also resembles the relationship of the capacitor. That means this very small, a few tens of nanometers, glass sphere behaves as an optical capacitor, a lumped capacitor. I was very happy that we found the equivalent of an optical nanocapacitor with light. But then we asked: how can we have the optical inductor? How can we have an optical resistor? Anyway, cut the long story short, we came up with the idea that you have these nanoparticles each made of different materials, one material could be dielectric like glass, another material could be a noble metal, like gold or silver, and another material could be a lossy material. Through our analysis, we found out that these three nanoparticles behave as a lumped capacitor, a lumped inductor, and a lumped resistor. We were very excited about this because we found a new alphabet that really merged the two fields of photonics and electronics together. Now, you might say: "OK. Very good, you have some nanoparticles that looks like a lumped optical capacitor, a lumped optical inductor, a lumped optical resistor. So what?" Then we showed the following: We showed that the designs already available and usefuls in electronics could be transplanted into nanophotonics. Why? Because in electronics, you know, that when you put an inductor and capacitor and resistor next to each other, you have a filter.

The same idea can now be transplanted in nanophotonics by putting one nanoparticle of glass next to one nanoparticle of silver, and then you can have a filter at optical frequencies, and that brings the two fields of nanophotonics and nanoelectronics together. Basically, with these optical nanocircuits there is now a two-way street of ideas going back and forth between the two fields. After this, we expanded our work into several different domains. For example, we came up with the idea of wireless at the nanoscale. The same way that you have a wireless system in which an antenna sends the signal, and the receiver receives it, we asked the following: can we do that at the nanoscale? If you have a nanoparticle that sends the optical signal by scattering or by lasing, then another nanoparticle can receive it. The same idea of wireless connection now comes in very, very small domain. Then we took that into graphene, a one-atom-thick structure. We said, OK, on a single sheet of graphene, different patches with different conductivity values can behave as lumped circuit elements. That would be the thinnest possible circuit element you can imagine, one atom thick. That idea connected us back to our metamaterial. We investigated how one can have a metamaterial on graphene. You can have a one-atom-thick metamaterial by just designing different patches of one single graphene with different conductivity. In that case, you have a very interesting system in which electromagnetic waves guide along this one-atom-thick layer, and goes around a specific pattern that you make on the graphene. It brings and connects different aspects of my ideas. That provided a very interesting platform in merging the fields together. Now we have a common alphabet, so rather than saying that in electrical engineering we have lumped circuit element and in optics we have lenses, mirrors, and so on, we say that both fields have lumped circuit elements, which in optics they are at the nanoscale.

When you put these nanoscale particles next to each other, you can have a nanoscale circuit. That was a precursor of my next idea of how we can have a material that would do optical processing? In electronics, you put circuit elements next to each other, you have an electronic processor. We said: "now that we have nanoparticles, can we think about putting them next to each other, and make a material that would do photonic processing?" That is what we showed. We designed a material that can solve equations with near speed of light when you send a wave through such material. It is an interesting journey, through my various scientific interests started with antenna which I started at Caltech, and now we are working in various aspects of nanoscale optics and nanophotonics, bringing in different mind sets into these fields—with also a little bit of biology coming in as a bio-inspired polarization image.

The Centrality of Structured Light

ZIERLER: Nader, bringing all of this research under one narrative, the way that you explained it, the way that you really told the story of your research career, one project led to another project, led to another project. If you can take me, going all the way back to Papas's lab, to what you're doing now, what is the narrative connecting point? Most fundamentally, is it the electron? Is it the wave? What is the one thing that is connecting everything from Caltech to today?

ENGHETA: Let me explain it in two words: structuring light. It really boils down to this, how to structure light. The common thread among all these is how we use materials to structure waves, starting with antennas, what's happening in the near field of antenna, how that connects to remote sensing, how the wave is being imprinted due to geological aspects, how electromagnetic wave interacts with the material chirality, how the handedness of a structure can affect electromagnetic fields and waves, and then how to design materials to manipulate and tailor waves to do unusual things. In the course of this journey, we had to come up with the alphabets of nanophotonics as lumped optical nanocircuits, inspired by electronics. That inspiration has had impact in nanophotonics, and that helped me to come up with material structures that can manipulate waves in order to solve equations. This comes back to the computation, and brings us back to the beginning of our discussion. I'm very, very excited to see how some of these ideas can affect artificial intelligence in the future.

ZIERLER: Nader, now that we've worked right up to the present, to wrap up this wonderful discussion, I'd like to ask a few retrospective questions about your career, then we'll end looking to the future. One thing we haven't really talked about a lot is your career as a mentor to students, to graduate students, to postdocs. What did you learn from Papas, and what have you made in your own mold, the way that you serve the next generation of students?

ENGHETA: First of all, I learned a lot from Professor Papas, not only how to do science but also how to mentor students and postdocs—they're our colleagues, I always treat them as colleagues, as equal—to instill in them the creativity and curiosity to pursue science and discovery. I think one of the interesting aspects of PhD education, any education in general but particularly PhD education, is to develop curiosity and creativity. Specific projects would be a tool to that end, but the main idea is how to develop one's creativity. That, I think, is one of the very important aspects of mentorship. To me, mentorship means giving the member the freedom to think creatively, to be courageous, to ask questions, wild questions, wild ideas. What if we do this? Why not that? Don't be afraid of that. Let's ask that question. What if questions? Why not questions? What if we have a near-zero index material? Can we make a near-zero index medium? What can we do with it? What would happen? Let's be courageous. Let's ask that.

I think developing the environment in which every member can develop one's creativity is very important. Another aspect of mentorship is to look at how ideas can help each other. Ideas are not individual silos. Ideas are connected. You can see from the examples I mentioned to you. That's why every member of my group has more than one project, because I say it's good to work on several ideas at the same time. There's no boundary among different ideas. The ideas can help each other. After all, nature is all connected. We can't separate chemistry from physics, from optics. They're all connected to each other. That, I think, is a very important aspect to instill in the next generation that you can achieve anything you put your mind to it. Also, another important aspect is to be very excited about what you do.

I always tell the students, "In order to convey the sense of excitement in what you are doing you should be excited about it yourself. When you're excited about what you work on, you can convey that excitement to others. Excitement is contagious." When I want to recruit students, I tell them: "We work as colleagues. I suggest ideas. If you are not interested in that idea, tell me about it right from the beginning. It's perfectly OK not to be excited about an idea, I can give you another idea. Maybe you are interested more on mathematical ideas. Maybe you're interested more on applied ideas. That's fine. I can give you those ideas, but don't just accept to work on an idea just because I say that. It's important that you would be interested in that. When you are interested on an idea, you put your efforts there, you get very excited, and this becomes fun, not just work." That sense of excitement is what I convey in my class when I give lectures. When I teach a class in optics and electromagnetics, from the beginning in the first lecture I tell them that this is a fun subject. Yes, it is a time-consuming subject, and you have to work hard, there's no question about it. But I do my best to teach you in such a way that you cannot unlearn it. By the time you finish my class, you will have learned many things about this subject. You will have learned the topics clearly, deeply, and intuitively. In other words, you will have learned not just the formulas but what's really happening behind those formulas.

No Favorites Among all the Research

ZIERLER: Nader, you've spent your entire professional career at one institution. It's an increasingly uncommon phenomenon. What has kept you at Penn all these years?

ENGHETA: A great environment, the freedom to work on any research project I want, wonderful colleagues—I've had great, wonderful, supportive colleagues in the past 36 years—and wonderful students, and again the ability to go and talk and collaborate with anyone you want. I gave you one example, Professor Edward Pugh. We started working in two different fields, and then we came together and developed a new field. I am very much thankful to Penn for giving me the chance of developing my career here, and I've been very happy with that. It's a great environment. As I mentioned to you, when I was deciding to come to Penn, one of the reasons I came here was that the atmosphere reminded me very much of Caltech.

ZIERLER: That's great.

ENGHETA: Small department and wonderful colleagues, and no boundaries among the departments. Really wonderful.

ZIERLER: In all of the discovery that you've been part of, that you've made possible, what has been most surprising to you, where you were led in a direction that you really didn't see coming?

ENGHETA: Good question. It's a tough question to answer because I love all the research topics that I've worked on over my career, and I'm confident that I'm going to like the future topics that I will work in the coming years. I like all of them, but I think one that would come to my mind is the near-zero index topic, because as I mentioned, it started with a simple what-if question, and that took me into a very interesting path which then expanded so widely. Now many groups all over the world are working on various aspects of the near-zero index structures and epsilon-near-zero media. But, as I mentioned, I love all research topics I worked on. One way or the other, every one of them has an interesting, pleasant surprise.

ZIERLER: In all of the ways that your research has been applied in fundamental science, in industry, what has been most personally satisfying to see where your research goes after it leaves your lab, after it leaves your research group?

ENGHETA: Again, I think all of them, one way or the other, have been satisfying to me.

ZIERLER: You talk about research like your children. You refuse to pick favorites.

ENGHETA: Exactly, that's exactly right. You said it beautifully. But I would say, for example, the metamaterial photonic processor, which is the material that functions as a computer, is something that can have a very interesting future direction and impacts on science and technology of computation. The near-zero-index photonics would also equally have impacts on, say, quantum science and thermal physics. The optical nanocircuitry is another one with high impacts. I remember back in 2005 when I was coming up with the idea of optical nanocircuitry and the nanoparticles functioning as lumped circuit elements with light, I was thinking that if I put them next to each other, can we do some form of information processing with light? Just like what you have in your iPhone, where you put the circuit elements next to each other, such circuits would do a lot of functionalities, I was thinking back then: "Can we do such functionalities with light with these nanoparticles arranged next to each other? That indeed turned out to be the case.

Of course, in this process, a lot of other things happened in between, but that shows the connections among the ideas we have. I always tell my students that serendipity is part of science. Always ask questions like these: what if? and why not? You never know where that would lead you to. You cannot predict the future, but also the future can bring some fascinating things for you which you could not imagine before.

Bridging Quantum and Classical Physics

ZIERLER: Nader, we've already talked about the Distinguished Alumni Award. We can't possibly cover all of the ways you've been honored and recognized in your career. I can't help but ask about two though. In 2020, you received the Max Born Award and the Isaac Newton Medal. I wonder if this ever caused you to think about your contributions both in quantum physics and in classical physics, and maybe your career is suggestive that maybe there shouldn't be these walls among the physics disciplines.

ENGHETA: Thank you, David. First of all, thank you so much for your kind words. I think you said it beautifully in a sense that connects to what I said at the beginning of our discussion. I don't consider myself either only an engineer or only a scientist. I am both. For example, some of the awards I received are engineering awards, but some other awards I received are pure physics awards such as the Isaac Newton Medal from Institute of Physics, UK, and the Max Born award from OPTICA. But also I had the IEEE Electromagnetics Award, which is an engineering award. I'm excited about the research, wherever it takes me. If it takes me to biology, I will go there. If it takes me to engineering, I will go there. If it takes me to physics, I will go there. I won't let the boundaries prevent me from going there. Again, I'm indebted to Caltech for this, because Caltech is an environment that nourishes you to think that way. No boundaries. One of the interesting points about Caltech is you learn to go after the scientific discovery wherever it is, and you go there regardless of where your department is.

ZIERLER: Finally, Nader, last question to wrap up our wonderful conversation. Looking to the future, I've come to appreciate that professors who lead research groups, when you reach a certain age, you have to start thinking about when you take on a new graduate student, that's a commitment of five, six, or seven years. Have you gotten to a point in your career where you're starting to think about a timeline where maybe it makes the most sense not to take on a graduate student at a certain point, or are you not there yet?

ENGHETA: I'm not there yet. [laugh]

ZIERLER: Great. [laugh]

ENGHETA: I'm not there yet. It's interesting, I love what I do, I've been doing it for 36 years, and I'm healthy, so hopefully I've several more years. One cannot predict the future but, no, I'm not there yet. I'm very excited about the work we are doing in my group, and I look forward to continuing that for the years to come.

ZIERLER: As an addendum to that, really the last question, for however long you want to remain active, what are the big questions that keep you loving working with the students, intent on further discovery, proud and amazed to come into work every day? What keeps things fresh for you?

ENGHETA: A lot of things. We touched upon some of them earlier in our conversation. One of the topics I'm very fascinated about, and I'm becoming more and more fascinated, is the physics of computations, and how my work and my group's work can impact the future of computation. One of the beautiful questions you asked is that during my lifetime, how the computation has changed. I told you, when I was an undergraduate, I had a little calculator, and now we are here with zoom. Literally every day, I think about this. What will happen 10 years from now, if we continue our work on metamaterial photonic computing machines which can do analog computations with the near speed of light, with much lower power, and much, much, much smaller size? Imagine that whatever the ability we have in our iPhone right now, in the future we will likely be able to do that in a volume one million times smaller. It would be a different world. I hope that I would be alive to see some of them during the remaining years of my life. The iPhone you have is computationally far more powerful than the computers in Apollo 11.

ZIERLER: Yes.

ENGHETA: Can you imagine what would happen 10 years from now? It would be very difficult to imagine. I remember, recently, I was reading a statement by Nikola Tesla in 1928—and I don't remember it verbatim—but basically what he was saying in those days, he was predicting what we would have as our cell phone in the pocket of our jacket, and we would be all connected. In 1928, he was predicting that, and we do have it now. We don't need to go several decades from now, but let's think about 10 years from now. What would happen if the speed of computation becomes near the speed of light, which is the fastest speed in the universe? In that case, we can do far more computation and with that we will have a completely new paradigm. What will that paradigm be? I don't know. Each of us can have some guesses for that. But just imagine. Right now, you mentioned about artificial intelligence and machine learning. Imagine we add to the AI the computational speed of photonic computing. What will happen?.

ZIERLER: What you're saying is you're really excited about the future, and you want to be around to be a part of it?

ENGHETA: Yeah, absolutely. Yes. I do my best to stay healthy so I can be around for that. [laugh]

ZIERLER: Nader, this has been a truly wonderful conversation. I'm so glad we were able to do this. I'd like to thank you so much.

ENGHETA: Thank you so much, David.

[End of Recording]