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Credit: Dan Pressman
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Interview of Lu Sham by David Zierler on October 22, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Interview with Lu Sham, Distinguished Professor of Physics Emeritus, University of California at San Diego. Sham recounts his childhood in Hong Kong and he describes the legacy of Japanese rule from World War II. He describes his early interests in math and he explains his decision to pursue a higher education in England at Imperial College. Sham discusses his motivation to conduct graduate work at Cambridge University and to study under Nevill Mott on the first principle method calculating the electron contribution to lattice vibration. He describes the help provided by John Ziman to secure his postdoctoral position at UC San Diego to work with Walter Kohn, and he describes the foundational collaboration and research that went into the Kohn-Sham equation and how this work builds on the classic debate between Einstein and Bohr. He describes the opportunities leading to his faculty appointment and eventual tenure on the physics faculty, and he explains the benefits of spending summers doing research at Bell Labs. Sham discusses his contributions to research on semiconductors, quantum computing, and density-functional theory. He describes his more recent interest in optics and the formative work he has done with graduate students and postdoctoral researchers over the years. Sham discusses his administrative service as department chair and Dean of Science. At the end of the interview, Sham asserts that the future of condensed matter physics holds limitless possibilities, and that improvements in semiconductor materials will push quantum information abilities in exciting and unforeseen directions.
Okay. This is David Zierler, oral historian for the American Institute of Physics. It is October 22, 2020. I am delighted to be here with Professor Lu Sham. Lu, thank you so much for joining me today.
It’s a pleasure.
Okay. So, to start, would you please tell me your title and institutional affiliation?
Okay. I am a Distinguished Professor Emeritus. So, I told all the people, including some funding agencies when they came to see us, that emeritus mean- it’s Latin. It means that a guy won’t quit (laughter). So, one of the visiting guys said, “Well, that was very effective. We won’t worry about you walking away from a project.”
Right. Right. They can stop paying you, but you won’t stop working, right?
Right, right. So that was fine.
And this is at, of course, UC San Diego.
Yes. I retired about 2012.
2012. Very good. All right. Lu, let’s go all the way back to the beginning. You have such an interesting personal background. I’d like to start first with your parents. Tell me a little bit about your mother and father and where they are from.
Okay. Let me tell you that I was born in Hong Kong in 1938. Both my parents came from Fuzhou, which was in Fujian, a province east of Canton, China. Hong Kong is south of Canton. Across the strait from Fujian is Taiwan, so you know where it is. My father was in the merchant navy, so he traveled a lot. So, I got a lot of stamps from him, and it was very good for trading because I got Venezuela’s. I don’t know how he got to Venezuela. Probably- (laughter). So yeah. I was very impressed when he was captain of a ship and kind of felt that his personality changed when he was on the ship and then when it was at sea. Then he was king of the hill there. It was very impressive to me. I don’t remember now-
Lu, where did your parents meet?
I don’t actually know, but the picture I have for them before I was born was that they were already in Hong Kong on a ship, and he was in uniform. So, I think they probably- they could have met in Fuzhou where they were born, but I never thought to ask when I was young (laughter).
Lu, what was your family’s experience, and yours because you probably remember the latter part of it. What was your family’s experience during World War II?
I don’t remember that. I do remember what my mother told me, in Hong Kong. So, we were under Japanese rule for three years and eight months. Everybody remembered that. The second war started for eastern Asians actually in 1938. For America it was 1942, right? So, there was a difference. Well, the Japanese got to Hong Kong. She always remembered- well, I remember she said that “We were out of food,” and so these Japanese had these dogs, kind of big dogs and they got fed those steaks, you know, just thrown at them. She always remembered that. So, my father passed away in a freak accident between Yokohama and Tokyo. He was in a ship docked in Yokohama, so he and the first officer went to Tokyo. On the way back, the overhead line fell and burned a whole compartment of those strings. Yeah. So, my mother was the one that brought up the three children.
Where were you as a child? Where did you grow up?
Hong Kong. I was born and grew up in Hong Kong.
What kind of school did you go to as a young boy?
Elementary school? Oh, yeah. I should explain in Hong Kong there are two kinds of schools. I went to Chinese school, and I would like to talk about the middle school. It’s called Puiching. Well actually, it’s not pronounced Puiching, but it’s easiest to spell as Puiching middle school. Those were my formative years and I remember best.
Lu, what was the language that your family spoke at home?
Oh. My family spoke four dialects, so as a result, I was not native enough in any of them. But I do better than all the visitors- (laughter). So, it was Mandarin. Everybody learned Mandarin—and Cantonese, of course. Cantonese was my first language and then Mandarin. Then Fujian- actually, its capital, Fuzhou’s dialect. The province is very mountainous, so their dielectric is difference from the neighboring areas, and then Shanghainese. My mother’s family was also from Fuzhou, but they went to Shanghai, so my mother speaks Shanghainese also. So, I got a little bit mixed up in that, too. That was useful for when I was in Portsmouth, England. The only Chinese friend I had was one who spoke Shanghainese, so I would speak Mandarin to him, and he would say things back in Shanghainese. Gradually I could understand it.
What was the language of your schooling? Was it English or was it Chinese?
It was a Chinese school, so Chinese was primary, but now I come to my experience. The teachers that influenced me, particularly the math teacher, Mr. Chu Tat-San. So, we spoke Cantonese during the class, but he was probably a university professor before he came to Hong Kong from mainland. So, this teacher was our class math teacher for the last three years, the senior years. In Hong Kong there were too many people at that time, so now I’m talking about 1950’s. I graduated in 1955, so the three years I was with him were ’53 to ’55. He was really overqualified, and I remember the three books we used were American university textbooks in English. He would explain things in Chinese and give all of the terms in English, and that was very good for us in later life. Also, we learned English. We could read English but had difficulty in expressing in it. It’s always those little words that were in everyday life that we did not know how to use. You know what I mean? Not the names of things; we know that. We can say “equation,” but not the description about them. We knew integration, but if you described it in words, we would be lost (laughter). So, Mr. Chu explained things in Chinese, and he was very good. We were very appreciative that he could actually pull it off with that. I remember we did geometry, trigonometry, and calculus. Algebra, he just assumed we’d done it.
What I remember in calculus, we had a tough time with integration, so he explained. He said, “Well, specifically which problem can’t you do?” and he would explain it. Then he’d say, “Okay. Is everything okay?” We’d say, “Yes.” “Okay. The next assignment will be doing every single problem in that chapter.” That book had one hundred problems from very simple ones to the tough ones. We did the whole one hundred, and about halfway through we finally figured out that if even if we didn’t understand why, we could still do it (laughter). It was very impressive. So that and the chemistry teacher really formed our science background, and it was not just our class, you know. The school can brag about a Nobel Prize winner, Dan Tsui, and a Fields medalist Shing-Tung Yao, both of whom I knew. They were both at least a couple of years behind us.
Lu, did you ever think about pursuing a career in mathematics, or did you know you always wanted to be a scientist?
No! Well, I wanted to go to sea like my father, to be in the merchant navy, to sail, to be a ship captain. My mother was against this. By that time my father had passed away and my mother managed to find three of his fellow students and close friends. They went to the naval schools. All three of them told me not to do it (laughter). So, I went to Portsmouth, England, for my higher education. Now I have to explain that. Because there are two tracks of schools in Hong Kong, my parents, my mother picked the Chinese school, I guess for cultural reasons, but there was also an English school and people- there were, of course, a lot of Chinese. The English schools made the students fluent in the language. They did not seem to get as a good education in sciences as we did, but that was the track to government services, and public, commercial, and all kinds of things.
Well, our class had 180 people in four classrooms when we graduated in 1955. More than half of them went to America. My mother sent me to England, first of all, because there was only one university, the University of Hong Kong, and you had to pass English, and our English was probably not up to it. In any case, there were so few opportunities with so many people, so I didn’t even bother trying. Everybody of my friends went to America, so I told my mother, “I would like to go to study there, too.” She said no. She saw on these news reels that there were- what is it? Panty races (laughter). I don’t know if you are old enough to remember that.
I’ve heard of them.
That put her off. She said, “You go to England instead of trying to study English in Hong Kong.” So that’s how it started. I said okay. If I had to go back to Hong Kong, I would be an engineer. At least if you did science, it would just be teaching jobs in those days. So, I went to Portsmouth, and Portsmouth was a technical college at that time. It’s now a university. It was an excellent place to be, actually. I was very lucky. I had to pass English. I had to pass the examination for the General Certificate of Education. So, I concentrated on that, and then our math, of course, was way beyond what they were doing, so I remember Dr. Haskell. He saw that I was in elementary GCE math class and he said, “Why don’t you take the first level General Certificate in autumn? In the meantime, come to my advanced math class.” I did, so I was way ahead of the normal class. I also took some engineering class and it was okay. These, of course, were engineers training for technical jobs, right? The only thing was the drafting. You had to learn how to do drafting, and this teacher was obviously a professional draftsman. I remember he had these thumb rules, and unfortunately, I was overeducated in Euclidian geometry. I could do all the drafts with a pair of compasses and a ruler without markings (laughter). You remember that?
So, I started doing that. Well, in two dimensions, it was easy. I kept arguing with him, so he was fed up with me; I was fed up with him. But in the end, he was actually right because when it came to three-dimensional rendering, you had to do these rules of thumb to get it right, to do projections that were complicated. It would take me all day to do a problem when he did it in ten minutes (laughter). But I said, “Okay. That’s not math.” And that was a required course, so I said, “Forget Engineering.” So, I concentrated on science. I did get five subjects in the school certificate, yes, all in the scholarship level so I could go to a good university.
And this is what prepared you for Imperial College.
Yeah. Actually, there was a story there. So, I had to take my general certificate examination the second year, and I applied to Oxford and Cambridge. They said, “No, you’re not qualified. We need you to have the certificates already.” I was not going to wait another year. Imperial College had an entrance exam. I passed the entrance exam, so they accepted me, and they even gave me a scholarship. Their scholarship was very important for English citizens because then they could get government subsidies, but I couldn’t. Even though I was a British subject, I was not a citizen of the United Kingdom in some ways.
Lu, did you focus on physics at Imperial?
No, math. I took a degree in math because I think that’s one of the formative things from Dr. Haskell. He was a brilliant teacher and a good mathematician. S,o I went to math.
And was your attention-
I should tell you partly I got put off by physics because there were always things that somebody would say, “Well, it can be proved. It’s just not for you yet.” You know? It would drive me nuts. Anything I didn’t understand I could not remember, so I said, “Forget physics” I like math, so I majored in math, but I was very lucky-
Lu, was the curriculum in math more applied math or abstract math?
Well, at that time I didn’t care. I liked everything, and there is a story there in how lucky I was. I did like the pure math, and the teachers were appreciative. They thought, “Did you get a degree already?” I said, “No. I just had these from Portsmouth Tech.” So, I liked the pure math, but in my third year, I really liked the physics part because I got these great teachers and they were famous. First of all, in quantum mechanics, they do it in three quarters- you know the quarter system. The first one was Harry Jones, and he was also the chairman of the department. He taught Schiff, so we got Schiff. That’s a common textbook in America. Well, we didn’t go through the whole book, but for a quarter we got all the basic quantum mechanics. In the second quarter, we had Abdus Salam. He came in. He blew through the entire book of Dirac (laughter). I wish I still had my notes. I had to take notes and read like mad, and with another friend, we really worked through it. I really liked it. Then there were also physics courses, and most of the things you can prove. There’s a logic to everything. Once you have logic, it’s easy to remember. So, I decided to go into physics. It took three years for BSc, so it’s a good thing. Compared to my friends who went to America, I was at least one year behind.
And this was 1960 when you graduated.
Yes. That would be 1960. So, I’m a little behind my high school classmates because of the system, and some of my friends actually graduated also in three years because they looked at the math in the first year and said, “We know it. We’ll just take an exam,” and then they were allowed to be in the sophomore year and so on. So, they finished in three years. Yeah. But there was actually a classmate, S. B. Woo who finished in two and then got a PhD. He later became the lieutenant governor in Delaware (laughter). In my last year I had a choice working with a pure mathematician on complex algebra. Professor Abdus Salam said, “Hey, you can join my group.” They were doing particle physics. You know, those were the years when he did the work that got him a Nobel Prize.
Yeah, on the electroweak theory. I only knew that later. So, I went and talked to his students who were already graduate students. They were very nice. They were very smart. They scared the hell out of me (laughter).
Do you know, Lu? Was Salam- were you aware? Was he in contact with Glashow and Weinberg during that time, or he was mostly working on his own?
No, I think he worked alone. Well, later on he actually became the director of the Institute of Theoretical Physics (ITP) in Trieste, and I got to go there quite a bit (laughter). The third choice for me was solid state physics partly because of Harry Jones. Mott and Jones wrote a book, so I read the book. It was very clearly done and a lot of math and so on, so I thought I would do that. So that’s how I became a condensed matter theorist. Then Harry Jones said, “Where are you going?” I said, “Well, a few places like Birmingham with Peierls,” because he got so many really first-rate people. So, Professor Jones said, “Oh. I’ll send a letter to Nevill Mott, and then you apply to Cambridge.” I got a scholarship at Churchill College and went to, the Cavendish Laboratory in Cambridge.
Why were you attracted, Lu, to go to Cambridge?
Well, it was one of the best schools then. It was great. Again, I was very happy at Imperial College. I was very happy in Cambridge because actually, Mott has a lot to do with it. Again, he is another Nobel Prize winner, and Harry Jones was also a member of the FRS, a Fellow of the Royal Society. They were all high achievers. It just turned out that way. You know, it’s almost like one passed me along to the other one. So, I went to see Sir Nevill Mott. At that time, he was called “the professor.”
“Oh. You have to see the professor first.” So, Professor Mott said, “Yes. Sham. Harry has very good things to say about you, so I will take you on. You go and visit the solid-state group first. If they won’t take you, I’ll take you as a student.”
What was he working on? What was his research at that time?
He was working on the transport of disordered electrons in solids. Yeah. His work was way ahead of the time. When I finished my thesis in May, I was floating around for a bit. So, he said, “Sham, come to my office. I have a problem for you.” He was doing on that problem. He explained it to me. He said, “Now you have all these Green’s functions. Go ahead and calculate them.” Well, I just couldn’t do it, didn’t understand what he wanted, and so on (laughter).
It was very funny, you know. Every afternoon at 2:00 I would get there. He would say, “Sherry.” So, he was the director of the Cavendish Laboratory, basically the Physics Department. For the administration, all he had was a secretary and she had to know everything. He would go around and said, “Sherry, where are my notes from the talk with Sham yesterday?” (laughter) That was how we started the afternoon for an hour. Then he had to do something else. It was interesting, but it was very- I guess, now come to think of it, what I learned was field theory. He thought that field theory could solve it, yes, but not in the way I was thinking, which was more perturbative, which yields a series that could be partially summed. His problem is a little different. It could perhaps be done with variational principles like the Feynman methods which I learned later, not at that time (laughter).
Lu, what was your thesis on? What was your research focus?
Okay. So, let me finish one more [story].
So, I went to see John Ziman. He was a very important figure, and that will tell you what my thesis was on. And then Volker Heine, who was younger and very friendly. So, we actually wrote a paper together. It was my second paper. So, my thesis was on electron-phonon interaction. Actually, Ziman, the first time I got an interview, he said, “Well, I’ve got other students wanting to join” you know, had a long list of people. “There are a lot of Cambridge graduates that want to do this, so you have to wait a while.” So, I had to go home. In the meantime, I was awarded a Churchill scholarship, so I went to Churchill College, which was a new college, wonderful. So, when I showed up the first day, Ziman said, “Yeah, I’ll take you.” He still had his galley proof of the book. I had already gotten the book. I actually used my bachelor’s degree prize money to buy that book (laughter). It was an expensive book, but I read it on vacation. It was a very good book, and I was very lucky. He gave me chapter five, “Electron-Phonon Interaction.” Phonons are the quantized vibration of the solids. The interaction with electrons was probably his specialty. But the other chapters, like chapter three, “Phonon-Phonon Interaction,” I read it and I didn’t know what was going on. It was only after I graduated when I was a postdoc—no, even when I was assistant professor, then I figured out I could solve the problem with field theory, but fortunately he didn’t give me that chapter. He gave me chapter five, looking at the electrons and phonons. I had to know the electrons, the structure, and the phonons, and then I could do the vibration dispersion curves of it. That’s where my Imperial College training of (laughter).
Yes. So, I was probably the first one that used the electronic computer, or in those days automatic machine, that was named EDSAC 2 . I was allowed to spend all evening running my program because I already showed that all my programs ran. So, I could do all the dispersions by computer and that was really good experience. That night, the engineer stayed with me till midnight. He said, “Well, it’s working fine, so I’m going home.” I said, “Yeah. Go ahead. I won’t be finished for quite a few hours,” and he said, “Okay. Here are the banks of the tubes. If it doesn’t work, it’s probably the vacuum tube racks in this shelve.” It’s like a library, you know, all these columns…shelves, right? He said, “Just try these. Pull one out and put another one in.” Fortunately, nothing happened. I didn’t have to do anything except sitting there (laughter). Then there was a book called The Black Cloud. It was written by Fred Hoyle, who was a physicist and who came to UCSD. He was at Cambridge. He wrote that book. It was clear he was sitting there in the same room, but probably with EDSAC 1 instead of EDSAC 2. He was all about this thing. I was reading it until daybreak. So, it was an interesting experience.
What I learned at Imperial College paid off in programming, and so I got my thesis on the electron-phonon interaction. It was about phonons for metal including the electrons, the interactions, and so on. I used the Bardeen formula and Debye-Waller factors in all of the phonon things. Then in 1962, there was a summer school, so I went to it. I think it’s in- yeah, it’s in Copenhagen. It was great. All the heroes in my thesis were there, so I got to talk to them! (laughter) Oh no, sorry. I got it wrong. It was in St. Andrews. Yeah, that was the school in St. Andrews, and Bardeen was an accomplished golfer. So, St. Andrews was the golfing place. Later when he visited us in La Jolla, I could see him in the afternoon because in the morning he went golfing. He was a county champion (laughter).
Lu, what did you see as your principal contributions to the field with your dissertation, with your thesis?
Oh, with my thesis, it was the first principle method calculating the electron contribution to lattice vibration. That was published in the Proceedings of the Royal Society after several rounds of editing. They didn’t like my writing (laughter). They said, “This is opaque.” So, for the thesis- and then electron-phonon interaction, of course, can be used for other uses. So, John Ziman and I wrote a chapter in the Solid-State Physics series by Seitz and Turnbull. Yeah.
And after you defended, what did you do next? What opportunities were available to you?
Well, I had two opportunities. We got a lot of visitors from America, and American professors were very friendly. They would just come and talk to the students. So, I had a standing offer in Chicago because of Morrel Cohen and Jim Phillips. They were very nice, easy to talk to. When John Ziman asked me where I was going. I said, “Well, I was looking around a bit, but I have an offer in Chicago.” He said, “Wait, wait, wait!” He was going to write to Walter Kohn and see if he would take me. Walter Kohn told me that he also wrote to Heine to make sure that I was up to it. So, the rest was history. I went to sunny California (laughter).
John Ziman is a very interesting guy and very, actually, insightful. First of all, he was a great writer. The second half of his career, he became interested in the social science of scientists, and he wrote well. He was the editor of the Cambridge Review then. Not many scientists actually were invited to be the editor, so he wrote well. Yeah. I really learned how to write when we collaborated on a paper.
Now in terms of teaching, his teaching was fine. Every week he got the group together. There would be a pop quiz. We would have to give a talk and to answer questions from a textbook. That was his teaching method and we could take courses also. But research- he was interviewed by BBC-3. They asked him, “How do you train your research students?” He said, “I throw them into the deep end of the pool and let them sink or swim” (laughter).
Lu, had you been to the United States before California or was this your first time?
That was my first time, yeah.
What were your impressions of California in the early 1960s?
Oh, it was very nice. Yes. In fact, the first time- yeah. It was perfect. Yeah. I was really grateful that John Ziman had the insight to get me and the other people to do what they were suited for. John Ziman was very helpful in other ways. The first time I gave a talk, I thought after London my English was pretty good, but he said, “I have a friend. She will train you for speech training.” It turns out she trains Shakespearean actors! (laughter) So I got that for, what, two quarters and then she said, “Well, you will do.” So that helped because, you know, I tend to hesitate. I still do that a lot. I tend to fade in sentences at the end so that it is hard to hear. But anyway, it was probably pretty bad if Ziman want to send me to speech tutorial. So, he was really very helpful. But he would let me work and he would answer questions if I got stuck and so on and suggest some methods and that’s about it. It was not very close supervision as we do in the States, but Cambridge tends to be like that. Some students in the first year got very frustrated when they got nowhere. Yeah. So, I have a friend who worked for Francis Crick and that was tough because he was a physicist trained and then he had to learn biology and so on. But eventually he got his research on track.
Lu, what was your initial appointment at San Diego? Was it a postdoctoral position or was it a faculty position?
No. I came as a postdoc. Yeah.
Who funded this? Who supported your postdoc research?
Oh, I came for Walter Kohn, so yeah. He had an ONR N andaval grant. He must have had a huge grant. He had lots of post-docs. He and Harry Suhl had lots of post-docs. I don’t even know who was who, and then we were all waiting for him (Walter Kohn) to show up. He was in Paris (laughter). He was in Paris until April, so he had one student there who came to me and said, “Walter Kohn said that you are going to supervise me” (laughter).
Now had you known Walter before? Had you corresponded with him at all?
Yeah, I corresponded with him. He was in Paris and I had not met him until April.
So, what was the initial connection? What attracted him to you or you to him initially?
Well, initially it was Ziman who said I should go to him. He checked with Heine and decided to accept me, and then how we got to work on… It’s an interesting story because he came back, and I remember that it was April. Then he wanted to give a seminar on the density functional theory that he did with Pierre Hohenberg. I spent a week with a Cambridge friend in Arizona in the Grand Canyon, so I rushed back and made it for the seminar. It was great. I can explain it a little bit to you, the physics of why that was great.
Please do, yes.
That work was important because you have to remember in the ’50s and ’60s, computers were getting better, so the computation of the electronic band structures in solids was getting very good. But the method they used was always the single particle band structure calculation, so there were some effective potentials that they knew. Then there were a lot of arguments and so on. I remember somebody told me that John Ziman in a conference I didn’t go to who gave the concluding remark and described the band structure work as “training the elephant to dance” (Laughter).
So, there’s this school of thought, and then there were people who had learned in the fifties how to do the electron interaction effects by the field theory methods of many-body interaction. That’s what I learned in Cambridge. I went to these classes by field theorists like Goldstone and then many-body classes by David Thouless. David Thouless was a fellow of the Churchill College, so I got to talk to him a lot. He later on got a Nobel Prize, so I got to learn from people who were first-rate and I didn’t know that! (laughter) But I did really learn things from them. But the trouble with these interaction theories for the solid is that the solid has to model the ions as a flat plane of positive charges. We call it a homogeneous electron gas. All the charges from the nuclei have to be just a constant. Each method had the strength of only one aspect and never the twain shall meet.
Then the density functional theory came at just the right time. It would marry the two things together. We could still use the one electron calculation, but we can get, in principle, all the electron interaction effects. I was there at the right time. With the tension between the one-electron band structure camp and the interacting electron gas camp, what Kohn told us about the theorem with Hohenberg in his seminar was like manna from heaven, right? (laughter) That was great, but I did have trouble using the method they had, which was a gradient summation, setting up the calculation. But the reason was kind of simple. Sometimes quantum mechanics is easier to do than semi-classical physics. In the gradient summation, the first thing that you do is the classical physics part, and the classical physics part is actually harder to compute. For example, the interaction people will use a billiard table for the interacting balls. It will be completely flat and level and then you talk about the billiard balls bouncing around with each other. The other camp would say that you have to have a periodic dents in on the table. Well, I can do the first. This periodic dents, that’s beyond my pay grade. It was very hard to do a single ball dynamics on a table with periodic dents, but if you allow me to use the Schrödinger equation, it’s easy to do it. So, then Walter Kohn and I had this Kohn-Sham equation which did just meld the two aspects. You use the density functionals to calculate an effective potential and then you do the single electron dynamics calculation.
Recently I have a hindsight. Last year the Materials Research Society gave me a theory award, and so I had to talk to people without using much math. I had to think of people wit wide range of interests in materials. First of all, there’s a picture you can use for what the Hohenberg and Kohn method is about. Technically, it’s that you have the potential of the periodic dents on the billiard table, and then from there you can find the density. Now, if you think about human population in the hills and dales as the topology, or if you like, the landscape. So, if you’re given the landscape, you can predict the population spread. The theorem says you can do it the other way around: given the population density distribution, you can figure out the landscape that produce the population distribution. It’s more useful the other way around, for example, because then you can start shaping the landscape with machines, leveling off the mountain and filling valleys. You will be able to control materials to suit your needs.
Then again, with hindsight, what they do is actually one classical result from an experiment, like I want to determine some property that depends on position, okay? So then, of course, you get that the theorem says that I can do it one way or the other. However, it involves the effects of the momentum, but you can now calculate from the momentum. So, the Kohn-Sham equation quantizes it back to a coexisting but incompatible momentum and position. I think of the Hohenberg-Kohn theorem doing the density functional as fine, but that is one slice of the quantum tomography. The reason in quantum systems you need tomography is because there are incompatible observables. Observables give you the properties. So, the position and the momentum are famously incompatible with each other.
Why? Can you explain a little more? What exactly is incompatible?
Oh. This is a classic argument between Einstein and Niels Bohr.
If it’s classical like a car, I’m going to Los Angeles from San Diego, I can figure out how fast I’m moving where I am at the same time. Yes? No problem.
If I have an electron, how do you measure the electron position? Well, you hit it with a photon. Well, the minute you hit it with a photon, it moves the electron. You can’t measure the momentum at the same time. So, Einstein would go do these gadgets and so on and then Niels Bohr would think about it for a night and then the next morning would come and say why that has a loophole. It was really interesting. They were in a Solvay Conference where they were allowed to think about it not just instantly. And similarly, if you want to measure the momentum of an electron, the electron got knocked off. They are just by measurement incompatible, so you just think of the two observables as incompatible. So, what the Kohn-Sham equation does is to recover partially the momentum. It’s not perfect, but my, so many people had used it now. Last time I looked it was about over 40,000 citations.
Lu, what was Walter Kohn like as a person? What was his research style and what was it like to collaborate with him?
He was very knowledgeable and very careful in his speech. He was a fatherly figure to me also. He would invite me home, but he was also a very busy guy. But he had a very strict way of mentoring which I learned from. He would have a student and then he would have a post-doc come and sit in the weekly meetings so the post-doc could work with the students. Yeah.
In terms of how the equations came about, what did you contribute and what did he contribute? How did that special relationship become this famous Kohn-Sham equation?
Well, it’s hard to say, to delineate this clearly, but it was clear that I complained. Since I couldn’t solve the single electron dynamics classically for the gradient method, I wanted to go back to the quantum mechanical Hartree equation. I just chopped off bits of his functional and called it the kinetic energy functional and solved the Hartree equation. So, he’d say, “Well, that was the kinetic energy of the single particle without interaction.” From there, it just bounced back and forth until we got the single particle Schrödinger equation with the so-called local density approximation, with the interaction effects from the free electron gas with the density at the particular position. During the galley proof theory, he said, “Wait a minute! This is completely general.” So, our general theory of the density-functional theory was a footnote added during proof-reading! (laughter) My friends always gave me trouble on that.
Lu, was your initial plan just to do a post-doc at San Diego, or was your intent to stay and make a career there?
No. I could go back to Cambridge. There was a fellowship waiting for me in Cambridge when I finished, but then I got married.
Did you take it? Did you go back to Cambridge?
Well, first of all, I delayed it for three years. They had asked at the beginning, “How many years are you going to be away?” I said two. It’s normally two, but then because our work was going well, Walter Kohn asked me to stay a third year because, really, we didn’t start this until late in the academic year, so it was kind of good that I stayed for three years and got the whole thing done. We got another paper out using the field theory method to get the single electron energy. Walter Kohn and Luttinger were also experts in that aspect for the homogeneous gas. He was a father figure in the following sense. Walter Kohn said, “Well, come and meet your uncle.” when I first met Luttinger (laughter). Then with Luttinger’s student, he would say, “Well, that’s your cousin” (laughter). So, he obviously had it all in mind, one big, happy family. Yeah. So, when he went to Santa Barbara, I went to see him. I always got to speak on his tens anniversary birthdays for about three times, yeah.
Lu, when did you join the faculty? When did that happen?
Oh. That’s in 1968. I went to UC Irvine in 1966-67 and then was given a readership at Queen Mary College, University of London 1967-68. Then I went back to La Jolla in 1968. In 1965 in La Jolla, I decided not to go back to Cambridge when I got married, because my wife’s family was in La Jolla, so we decided to stay in America. I was looking around in America. I got an offer at Irvine. I met Alex Maradudin in a meeting. He was a very nice fellow and we talked a lot about phonons, his area of expertise.
Lu, I want to ask at this point. Did you seriously consider Bell Laboratories? That must have been a very attractive opportunity for you.
I spent many summers there. Yes. Yes. I’d actually been to Bell Labs quite a bit because Phil Anderson was a visitor in Cambridge also, and he was, also, a very nice guy. So, I get to know all these nice people. Phil Anderson was at Bell Labs. But I saw all these bright people there. I chickened out. Also, Bell Labs was a temporary position. It was not a tenured position. It’s like a second post-doc and then they decided whether to keep you on or not. So, I took the academic position, but it only lasted one year and then I got an offer I could not refuse which was a tenured position in London, Queen Mary College. They gave me a readership. My wife and I enjoyed London and lived in Kent a lot. She found work, so we spent a lot of time in West End theatres and concerts. But we couldn’t imagine how to raise a family there, so we returned to the States.
Yes, so we came back and then San Diego decided to take me. I picked that one. Three campuses had an invitation, but Georgina’s family is in San Diego, so it was easier.
Lu, how big was the department at San Diego at that time? Was it still pretty small or was it growing?
It was top heavy, and they were all first-rate people. They would all had to retire in the early nineteen nineties, so when I was dean, I had to prepare the department so that before it started, they could attract good people. If we waited for them to retire, then that wouldn’t had worked.
So, I thought five years before that they should start hiring the third generation. I was kind of the second generation.
Lu, when you got back to San Diego, what was your research? What were you doing at that point?
Well, let me see. I actually started doing more on semiconductors, and I did not set up, which maybe I should have, kind of a computational group to exploit the density functional theory. In fact, I wanted to move on, so I started doing dynamics. Yeah. If I could just take a look at my notes.
What did I do next? Yeah, ’68- that’s going back. Yeah. So, I started basically a lot of things in optics. That would give me the dynamics and so on. I was very interested in semiconductors, a small number of electrons; it’s easy to control. So, then I spent a lot of time at Bell Labs also. In fact, at first, I worked on diamond. A postdoc, Werner Hanke and I did a lot of work on the band structures and optical properties and so on in the summer, so they asked me to give a talk. There were about twenty people there, and I thought that was normal. My friend Phil Platzman said, “Next time you come, you do it on silicon. You’ll see how many people will come.” So, I went back, got Werner working on Silicon, giving the exchange and correlation effects on the optical spectrum. Phil was right. A lot more people came to the Si seminar (laughter).
What were some of the major questions in this field as you got involved?
Well, so later on came quantum computing and information processing. I remember that in 1998 I was on sabbatical in Berkeley. It was great. They gave me a Miller Fellowship so that I didn’t have to worry about half pay and grants and stuff. I could talk to a lot of people. I talked to Ron Shen and a lot of theorists, Marvin Cohen and Steve Louie and their group on band structures. We talked a lot, but then a post-doc came and talked to me about quantum computing. I said, “I don’t know anything about it. Tell me.” Then gradually the dribbles of students came to talk to me. So, I said, “Well, how come you don’t talk to your professor?” One postdoc, Daniel Liddar, who was working with Professor Birgitta Whaley on quantum computing, told me about their work. Birgitta also invited me to join the seminars in her group. Daniel later did great work in quantum computing. But in 1998, mostly the students said, “My professors don’t believe quantum computing will work, so they won’t even discuss it.” These guys set up Saturday workshops and got people who had started doing work on it, so because I was doing optics, I said, “Get some quantum optics people. They are very close to the quantum computing development.” They liked that.
I went home and told my poor student (Pochung Chen). I said, “Would you mind changing subjects?” He said, “No, it’s fine. Let’s go for it,” and he did a great job of it. We were just doing two-qubit dynamics for semiconductor excitons, and he was leading the computation part. He sketched this way and that way, and I said, “No, I think it’s easier if you do that.” He said, “Well, prove it. I’ll give you twenty-four hours” (laughter). I had to sketch the proof and then let him, and the post-doc prove it and then… Well, I basically demonstrated how it was possible, but they had to cross all the T’s and dot all the I’s. So, they did that and Pochung ran the program. It actually kind of worked, amazingly. It was kind of complicated.
By that point, I was way behind in quantum computing, so that’s how we got started, and then I met Duncan Steel of Michigan. He was professor of physics, engineering, and biology. It was funny how we met. It was the first time I was invited to give a talk in the Optical Society of America. There were a lot of people there. There was this bearded guy in the back who had a lot of questions, almost like heckling. So, when I finished, I went to him and said, “You need to explain your terms to me,” and he said, “Well, you need to explain your terms to me.” I said, “Okay, that’s good. We are in two different languages. From now on, every time we say something, we translate” (laughter). And then the friendship actually grew from there!
So, then we decided to collaborate. Then there was a third group, Dan Gammon in Naval Research Labs, that could make these quantum dots, semiconductor dots, which was perfect. I knew the optics of quantum heterostructures, so Duncan made up the collaboration team. I said, “Well, we’ll go for a grant and so on, but you have to show that you can get a Rabi rotation of these things.” He did that, and I learned how experimentalists worked. One step at a time, he took the thing. He did all the spectra. He got the sample from Dan, his group did the spectroscopy, and then he, one step at a time, built it up to there. Then he knew exactly what he had, and it was very interesting for me. Working with Duncan was working in real time. They were going to do the next experiment. It was just like my student Pochung who gave me twenty-four hours (laughter).
Lu, at this point, I think it’s a great place to ask how were computers, the growing computational power that was occurring at this time? In what ways did that influence and expand the possibilities of your research?
Oh. Completely dependent on that. It’s good to have powerful computing and I’ll tell you why. I remember that the density-functional theory, that paper now has 40,000 citations, was kind of ignored in the beginning. But my friend Sam Trickey organized a thirty-year anniversary book. Then you’re beginning to see that because people can use the computer, they can do complicated things on it. You know, the computational difficulty exponentiates with the number of particles you have, right, so it’s not going to work. So, we cut off a lot of that. You need to build the functionals. There were a lot of chemists who were very good in building functionals that work for molecules, and so some of my best friends are chemists (laughter).
Lu, how did your work on density-functional theory change over time? Did you remain close to it or did you generally move on to other research pursuits?
I moved on. As I said, I moved on to optics, but then when I was at Bell Labs, Michael Schluter came to me and said, “You know, I want you to solve a problem.” The density-functional theory with the local density approximation, which was I’m using an electron gas at every location so that when the density changes, I change the location. I change the interaction and so on. That apparently works, but then it has a defect. He said, “It has a defect. The band gaps of the semiconductors you get is always two-thirds of the measured ones. Now you can’t escape that.” I said, “Whoops. Go back to the drawing board. We’re going to redo it with field theory.” As it turned out, I already tried doing it, so I had the first paper with that, and then with him we started making models. He was a great guy in computation and in talking about physics, too. He and Rex Godby, the three of us worked, so we could explain what happened with the band gap differences. I really was upset when he passed away from brain cancer. For a while I just couldn’t worked and didn’t want to hear about density-functional theory.
It’s because the free electrons don’t have a gap, so when you go from no gap to gap, there’s a phase transition. There’s a jump. So, if you filled up the Fermi levels, you filled up the electrons to the gap and then to the energy, then there’s a gap and there’s a jump. Well, if there’s a jump, everything jumps. The energy jumps- well, not jump. At least the energy would change its slope, right? So, one electron, it will change its slope. It changes it drastically and you have to calculate that, and then you cannot use the local density approximation. So, with the field theory, we could get the formula for the band gap.
Then Michael Schluter and Rex Godby would program that at Bell and ran at the machine that Bell got with NSF funding. The program was in my name, so people were coming into me and saying, “We were wondering who Lu Sham was who kept using up the input and output of the computer all day long, so we’re going to come and murder you” (laughter). I said, “Well, I had the time directly from NSF. You guys didn’t pay for it” (laughter). Our computation was complication and we could not afford to repeat the procedure all the time. We made tables and moved the table in and out. We could reproduce the gap for many semiconductors, and that was a proof also that LDA won’t work but people already had been making a lot of useful modifications. But, the elegance of the LDA that we used was gone. That’s where it’s good to have the computer power. You don’t care so much about elegance.
Lu, what were some of your graduate students working on at this time in terms of representing where the field was headed into the future?
Well, that’s where my last hurrah was on the quantum computing of the single quantum dots. So, we did a lot of optical controls, and we also- one important thing is that you can confine a single electron and then Duncan can optically control it and then we make theories of that. But there was one very important thing, and it was kind of an interesting thing. I had a post-doc, Ren-Bao Liu, and two students, Wang Yao, and Sophia Economou. Economou and Wang joined my group first and then Ren-Bao. The four of us worked on a most important effect called decoherence. The qubit works because you can make a superposition of states. I’m just telling the undergraduates right now- I have a first-year seminar series for them. You know, it’s like you will have properties of the components, but it has its own property. You put the two slides yellow and blue on top of each other; you get green. Then you could parallel process the superposed state. That’s an important thing. But that superposition is very fragile.
The optical people were very nice. The French, they were very polite, and they said, “Well, we’re really worried about you. I wish it would work, but it won’t work. You have all these other electrons.” I said, “Don’t worry about electrons. We isolate it by frequency.” But what we could not isolate is that because we wanted to do it optically, our materials had nucleus spins. If you do it with silicon, you don’t have nucleus spins, but then you don’t have optical control. Optical control has a lot of bandwidth, so I wanted to stick with Duncan and just worked with the optically active materials. So we said, “Well, we’ll go in and study how a nucleus spin reacts,” and I told Yao and Liu, “I want you to do it quantum mechanically and go and do a literature search and see whether somebody has treated nuclear quantum mechanically.” They came back with only one paper that treated the nuclear spins quantum mechanically. Now all three, as professors, are taking the quantum research to new heights, Sophia in Virginia Tech, Wang in Hong Kong U. and Ren-Bao in Chinese U. of Hong Kong.
What were the challenges in pursuing this, Lu?
The challenge is to keep the coherence of the qubit long enough for computation. Well, then we had to study the quantum mechanical dynamics of the nucleus spins, while they were interacting with the single electron. So, we could do it; we did it. But to convince my group that we had to do it, I sent them to do a literature search to see if this was done already. They came back with a bunch of papers, but they all had these stochastic assumptions, which means they already treated the noise problem classically. I wanted a quantum mechanical theory, so only one such paper by Philip Stamp. He had a molecule and could assume all the interactions were the same throughout. Then he and his coauthor solved it exactly. He did a lot of work on the environmental decoherence. We became friends because of our related work.
But I told my people, “That’s not good enough for our single electron system” so we went and did it for the single isolated electron. We understood how the agitations of nuclear spins could be quietened. The common method at the time was to average out the distribution of the nuclear spin polarizations from the Overhauser effect that destroyed the coherence of the spin states for quantum computing or quantum information. On the other hand, Walter Knight at Berkeley first discovered that the electron also provided a magnetic field that would line up with the nucleus spins. So, if we keep those spins straight, then maybe the disorder would calm down. We actually didn’t think that would work because one had to be able to move the electrons spins. If you want a quantum computation process; you need dynamics, so how is that going to work? We had a lot of schemes that people used that we could borrow. So, we picked a scheme. that worked out well in theory. Then Duncan Steel said, “Okay. While you are sorting out the theory, I just got the students to keep the laser on for a long time and see what happens” (laughter). What happened was that the coherence lifetime went up three orders of magnitude! He said, “I could not put it in the papers, but I believe it’s more. We don’t have enough accuracy to measure more than three orders of magnitude narrowing of the resonance line.”
What was the limiting factor to prevent greater accuracy?
Because they could not measure the spectrum beyond certain limit.
You see? Duncan’s group could measure, say, a resonance peak in the optical spectrum but the width of the peak at half the height of the peak was smaller than the accuracy of their measurement instrument. So, their continuous use of the laser was a good method because after the narrow peak was established, the student could then leave the laser off for an hour and then came back to find the peak still there. Then we did not need the fancy theoretical method we established to stabilize the nuclear spins. And you can always refresh as in classical electronic circuits, so that’s not a problem. We thought that would work, but then the superconducting qubits came along; they could do a lot more things. Our problem was how to connect two of spin qubits in two different semiconductor quantum dots. That was a tough problem. Duncan’s group did demonstrate entangling a spin with a photon, but then we kind of ran out of time and got superseded by the superconducting circuits for quantum processing. But, I’m hopeful that later on, semiconductor quantum information processing and computing will develop.
Lu, what were some of the theoretical and experimental advances that made your research possible at this point?
I think a lot of very good models that people do. People who know information theory and quantum optics tend to be very good at that, so I tend to study their papers a lot. There’s really real progress in materials and then quantum materials that we might be able to use and also theories for information processing. It’s nice to have work forcing you to keep up with it, but I don’t think I’m keeping up that well. I think things are developing; especially the companies are now doing it, except currently they’re all betting on superconductors. But there’s a lot we can learn from the superconductor quantum technology.
Lu, I’d like to ask you about your work on the administrative side as chair of the department and then later on as dean. Were you able to keep up with your research, or did these responsibilities really pull you in different directions?
That’s why I was a short-term dean and- yeah, one-term chair. Actually, I did the opposite way. My administrative career went south (laughter). I was dean first and then I was chair (laughter). So yeah, when I was dean, I kept a group going with some really good postdocs and students.
And this is dean of what? Dean of Science?
At that time, Dean of Division of Natural Sciences. It had four departments: math, biology, physics, and chemistry. They were all big departments, so all told, about 200 faculty or maybe more. Biology is actually the biggest. They’re really good departments. Biology I particularly treasure. The assistant professors that they recruited were always ranked number one, so I was impressed. They were tops and they made good progress. But all four departments were good.
Did you ever find it difficult, Lu, as dean to compete for resources within the California system given how enormous Berkeley and UCLA were?
Yes, but I went in at a good time and got out at a good time. There were fifteen years that the budget was flat-lined. When I went in, I saw that the state budget was going up, so I had the departments give me a five-year plan. In the physics department, it was Harry Suhl, who is a humorous type, so he handed me a graph which I used a lot. It said that the mean age of the faculty in the last seven years, plotted as the mean age of the faculty versus the year was a forty-five-degree line. So, the graph indicated that, “We need people.” Chemistry and biology needed building and infrastructures before they could expand. Math needed more faculty. Chemistry and biology needed space, so I pushed for that. Another physicist was the Vice Chancellor for Academic Affairs, Harold Ticho, who understood Physics’ curve. We deans and administrators had to meet as a so-called budget committee. So, Ticho distributed that curve graphs and people asked, “What does it mean? Why are you laughing with Lu?” He said, “Oh, Lu wants all the faculty allocations” (laughter). So, I pushed for that and yeah, pushed for a big lab building for biology and chemistry and early recruiting for physics and math. So, I broke the administrative rules that everybody would get the same thing. The original plan was to build a new building for three departments. And I had a psychological advantage. I planned to be a one-term dean, so I didn’t care about repercussions (laughter).
Did you become chair right after you stepped down as dean or not?
No. I got a year away (laughter). A sabbatical, and then I came back and then there was a delegation that said, “While you were away, the department was very split and we would like you to chair.” I said, “No. Come on.” Well, I didn’t answer part of one of your questions: what about my research while being a dean? I kept my research group. My friends who went to the meetings didn’t know about my dean responsibility until later on someone heard about it and they said, “Oh, in all these years, how did you keep it up?” Well, it was kind of tough.
I would set Thursday as the day, “Unless the sky falls down, I’ll be in my office seeing my group people.” So that’s how it worked, except of course the sky fell down a lot (laughter). But the students were hard work and took my absence in stride. Well, I didn’t have a very big group, and I don’t remember how many, three or four. I had a wonderful student, Takeshi Uenoyama on sabbatical leave from Matsushita Research Lab in Japan. He had such a different working culture that it was amazing. I said I would always see him at 6:00 pm when I got everything done in the dean’s office. He would always be in my faculty office every day. We had a party at home. Mrs. Uenoyama came to me and thank me profusely, “My husband is home every day for dinner with our child. In Japan, he came home too late to see our daughter” (laughter). I was amazed. On the other hand, there was one guy who said, “No, not at six. I’m going home. I’m a nine to five guy.” I said, “That won’t work even under normal circumstances.” It turned out his wife acted the same way in biology. They said, “Life is more important than work.” So that was tough. Yeah.
Takashi was a little more mature than the rest of my group. He was the leader of a group in the Matsushita research lab. Matsushita was a gigantic company. It’s like General Electric, right? Did everything. So, in the research lab, he was the head of a three-man group on integration in circuit designs, and he just got tired of it. He wanted a PhD so he could do other things, and so he came. He came for a year. The company really was generous. He got a nice apartment and everything. Then he said he wanted to do a PhD with me. I said, “Okay. If you have any funding problems, I will support you with my NSF grant,” but then of course, the student’s stipend would be much lower.
So, he went home and asked for a leave of absence. The Lab really wouldn’t give it to him. He said he would quit. That got people’s notice, so he stayed on to try to convince the Lab administration. After a month he came back. He lost weight. He was skinny already. It was really stressful for him. His parents didn’t agree with him, but his in-laws were very supportive. That was a very interesting cultural experience for me. Then they lived in the graduate student dorms and lived like the graduate student. He got his PhD in two years. I said, “I cannot excuse you from any exams,” so he went to take the oral exam. I was not allowed to go, and I was worried about his language problem. I asked Professor Harry Suhl who chaired the exam committee, “How did he do?” He said, “Perfect.” I said, “You understood his Japanese English?” “No, but I understood his Japanese physics.” Very clear. He could answer questions. He knew what he was talking about.
So, I survived with a couple of other people like that and I kept things going pretty well when I was dean. When I was chair, it was supposed to be easier, but that took a lot of time. When I was dean, I boasted that I never took any administrative work home, and somebody at a party said, “Check with your wife. She said that you were never home anyway” (laughter). Well, not quite true, but it had long hours.
What do you see as some of your big successes as chair?
When I was dean, the astro people felt a little neglected. They wanted to have a separate department. Margaret Burbidge, who was of course a giant figure in the field, came and talked to me. They have a separate institute, Center for Astrophysics and Space Sciences. Margaret was the director. I said, “There are people in CASS who like to talk to physicists because they are actually astrophysicists. But I don’t want to argue with you. This is going to be the economic picture.” I’d been on the university budget committee. I knew how they counted heads and what kind of allocation you would have. The astro people said, “Well, we’ll teach undergraduates, large classes” but the required courses are the ones that took the most people would get the most allocation. With a few I think well justified concessions, we had peace with the people in CASS.
Oh yeah, when I was dean, the other thing that I complained about was the inequity of the return of research overhead to the San Diego campus compared with the others in the University of California system. San Diego, especially my division, had the highest research funding excluding the Medical School. Sorry, I keep answering your question several Q&A’s down the line. It seemed that we are mistreated because we only got back at that time about twenty percent of the income or less. It’s like the state of California in USA, we pay a lot of taxes and not getting our share back.
So, we’re supporting these big dudes (campuses) also. Well, we didn’t have enough students, as they counted undergraduates. I wanted physics to have a building when I was chair. That was tough.
Did you get it?
No. Eventually we got an extension, which was nice.
Lu, just to bring the discussion all the way up to the present, in what ways have you been involved in physics since you went emeritus? What have you been doing in recent years?
Oh, I’ve been doing research. Yeah. I cut the size down. The advantage is that I can get my hands dirty.
A disadvantage is that there is no effect to even out the ups and downs. If you have one incapable person, that would a big loss. Yeah. Then gradually our funding got smaller and smaller, and then I only got half a post-doc and I had to save it till a time I could afford a full-time postdoc.
So, I did the work myself when there was no help. Of course, it’s not as much work as a full-time faculty. I don’t have to teach. I don’t have to attend committee meetings. I did have to go back and teach once when they were shorthanded right after I retired. They said, “Well, you’re supposed to give me five years’ notice.” “No, I cannot do it.” The vice chair was joking, but he said, “Well, I really need you next year,” so I said, “Okay. If you’ll let me retire now, I’ll do it” (laughter). It was the third quarter of quantum mechanics. Nobody wanted to do it.
Lu, on teaching, what had been some of the most enjoyable physics classes to teach undergraduates for you? What do you like teaching the most?
Quantum. Yeah. It started with a graduate class and then undergraduate. I had a very good graduate class, and it was not very large at that time. There were about twenty-some people, and that’s where I got my best research student at that time. There were some really brilliant students like Sophia Economou and Wang Yao. What I did was I said, “You know, these guys are in their first year.” Many first-year graduate students were tired of course and wanted to do research but the first year was entirely devoted to required courses and one or two electives. There was normally no opportunity for research. I made the homework as mini-research.
So, what I did was I gave them homework problems—only three homework problems a week, so they were quite meaty problems, and the students were formed into three groups of three each with one chair. I nominated the chair and I made up the group. I didn’t want buddies together. In fact, just the opposite. If I knew they were buddies, I put them in different groups (laughter). Every week, three persons gave a talk, the chair of the small committee was responsible to coordinate the problem solving and the talks. They got a whole afternoon with me and then the class got a different afternoon. They loved it. They loved the afternoon and always showed up. They said, “It’s like research.” The problem session became a seminar when the peers asking questions seemed to make things more relaxed. So that was very popular. In fact, it was so popular that they said, “This hour and a half thing is not enough. Can we schedule a whole evening?” So, with my wife’s permission we had it one evening a week. Somebody would bring baked bread and other stuff (laughter). So, we just kind of didn’t care how much time. I finally had to say, “Hey, fellas. I don’t know about you, but I’m tired.” Then a plasma theorist heard about it from the students, so he told me that he tried and was glad about it.
That kind of problem session really was useful, and it was very enjoyable because you got real feedback. They had to explain the way they thought and could really get into it. And it showed people thought very differently. There was a guy who would make a great experimentalist. He didn’t do any math with that program, but he explained the whole thing thoroughly and got the answer- not quantitatively, but qualitatively. He got the answer. I immediately pointed out, “Do you guys see that some of the theories aren’t needed to solve the problem?” There were criticisms: “You didn’t give us a figure!” “What are you talking about?” So, I had to explain what he had achieved and why that is very important that one actually could do that. Those were amazing things, and it was amazing that the students would act at such a high standard. In a big class, the scheme was a mess. There were students who never did their homework and just copied down answers and submitted as late homework. So, I had to put in restrictions. None speakers had to turn in their homework before the session, etc.
So, when it was a big class, I started posting all the homework. I said, “You guys had better do the work. You can’t just turn in the homework late and so on.” I did get a TA who policed all the processes, but I still wanted to chair the presentation session myself. But that did not work nearly as well. There’s no camaraderie in it. It was that atmosphere that I really enjoyed in the evenings when it went well. People were pushing for the same thing. They asked questions, but there was nobody who would kind of ask questions to be one-up on other people, which would be very unpleasant because we’re still learning, right? So, I had a very good time teaching that, but of course, all good things come to an end because after four years, the vice chair said, “Nobody got to do the quantum classes for four years in a row” (laughter). Quantum was a subject that many faculty members wanted to teach.
Well, Lu, for my last question, I want to ask you looking forward, either in terms of your own research or as a representative of the field, what are the things that are most optimistic for you or exciting in superconductivity, in semiconductors? What are those things that are most compelling to you as the field progresses forward into the future?
Oh, I think the future is limitless. They can now make superconductors of all kinds of quantum materials for all kinds of reasons. I’m not even in a position to guess what it will be, but I think that, with the advantage of the industrial base, the semiconductor materials may eventually become a player in quantum information processes and then, with a breakthrough in large scale circuit integration, in quantum computers. With the national push of quantum education for K through twelve, I personally am now more concentrated on seeing if I can get the beginners who have missed such K-twelve education into quantum things, no matter what they do, because those are really interesting things. It needs practice to keep up.
What do you think are the prospects for true quantum computing? How close are we to that?
Let’s see. If I may quote William Phillips, Nobel Laureate in Physics (1997), about ten or twenty years ago, he said, “fifty-fifty. It means fifty years with fifty percent chance of getting it” (laughter). But that is not the question. How can you use quantum technology to do simpler things first, like a trigger? Then you can ask how to build devices of the next level, etc. I knew that people wanted to murder me when I said that in a workshop, but I wasn’t the only one that said, “You can make little gadgets that are even semi-quantum or just very small gadgets.” Well, that’s how we can do cryptography, so that will come very quickly. Already they are selling it.
One of our post-docs, about ten or fifteen years ago, a headhunter tried to get him to go to work in Massachusetts for a company that’s selling entangled qubits for action at a distance. You send one of the two entangled qubits to Alice and the other to Bob, those would be the basis for safe secret communication (laughter). So, it’s a commercial thing now already. And now there are commercial concerns that are training quantum workers. I think preparing them in academics is pretty good, so that’s my little contribution is to dip my toe in training students outside research. I do not know how the NSF effort is for K-twelve (laughter).
They’ll figure it out (laughter).
Yeah, they have a huge collective effort supported by computer industry. I don’t know what the organization structure is, and how it is supported by all the named computer companies (laughter). So that’s an interesting societal development also, isn’t it? It’s not just quantum computing. I would also like to see how you use the new quantum materials for technology.
Well, Lu, I want to thank you for spending this time with me. I’ve had such an enjoyable time listening to all of your recollections and explanations of the science. It’s a remarkably important history that you have to share with me, so I really want to thank you for doing this. So many people will gain so much value from this transcript once we have it ready for publication, so I really appreciate it.
Well, thank you. I enjoyed the conversion!