Eli Yablonovitch

Zierler:

Okay, this is David Zierler, Oral Historian for the American Institute of Physics. It is April 4, 2021. I'm delighted to be here with Professor Eli Yablonovitch. Eli, it is great to see you. Thank you for joining me.

Yablonovitch:

It's my great pleasure. I think you're performing a very valuable function for posterity.

Zierler:

I appreciate that. To get started, will you please tell me your title and institutional affiliation?

Yablonovitch:

So, I'm a Professor of Electrical Engineering and Computer Sciences at the University of California Berkeley. And I have some other titles, but that's the main one.

Zierler:

Let's get our terms on the table right off the bat. So, there's Electrical Engineering, there's Computer Science, and there's Applied Physics. Where are these boundaries for you, and over the course of your career, have they been more or less fixed or not over time?

Yablonovitch:

Well, that's a really deep question. I think Applied Physics, if we look back historically, is physics for the Defense Department, to be quite candid about it. And so, there are a lot of special things that the Defense Department needs, and people do it. And we have departments of Applied Physics in some of the top universities. But what those universities have in common is that they're well-funded by the Defense Department. Now, if you go beyond that into, "Shouldn't applied be more business-oriented?" And there, it becomes a little more iffy. It's a bit more vague, and what's business-oriented changes rapidly with time. Over the years, the nature of business has changed enormously. And the distinction between Electrical Engineering and Computer Science, which was the last part of what you asked me, is sort of interesting. Very few universities actually have those as joint departments, and I think it brings strength to both fields by having them together. Though, even some of my colleagues in a joint department would prefer to be separate, and I think it's wrong and not very constructive to separate those two functions. I think that answers some of what you asked.

Zierler:

How have your research, collaborations, and ventures fared over the pandemic?

Yablonovitch:

It's been terrible. I like to be around people, and I've been sitting here at home. And I'm in the age bracket where I have something to worry about. Although I'm actually quite healthy, people in my age bracket have more to fear than younger people. So, I don't like the fact that I've been stuck at home, and I'm glad that the pandemic is just about ending right now.

Zierler:

To give a concrete example, what was something that you were planning on doing over this past year that either got stuck completely or is nowhere near as far developed as you'd hoped?

Yablonovitch:

There were a whole series of scientific conferences that were canceled. I taught two classes remotely. I didn't like it. I prefer to look the students in the eye and get reactions from their facial expressions. So, it's not been great.

Zierler:

Let's take it all the way back to the beginning. Let's start with your parents. We'll go back to Europe. Tell me about them and where they're from.

Yablonovitch:

My father is Polish-Jewish, and my mother is Russian-Jewish. But it's a much more complicated story, and I'm planning to write a book about their life experiences. They both survived World War II at a time when only a minority of their compatriots survived. And so, every survival has a story to it.

Zierler:

Did they meet before or after the war?

Yablonovitch:

They met just as the war was ending. And I'm going to give you a little taste of why there's a book in there. When I was growing up, my mother was a great partisan of Russian culture. And I grew up in Montreal, Canada. And she found all the other Russian ladies in Montreal. And she organized a weekly meeting for them, on Friday nights. And these ladies met for fifty years. Which is totally amazing that this went on, and on, and on for fifty years. And they used to come to my house. We had a relatively small house. It would rotate weekly among the ladies who would then converge on my little house or flat twice a year. And the house would fill with thirty, forty Russian ladies, all yapping away in Russian, which I didn't understand. And it was sort of a relief, "Oh, they're gone now." It happened roughly twice a year because there were thirty of them, so twice a year it would be my mother's turn.

And then, I got to know them. They were all interesting ladies. But every one of them had a Polish husband. And at that time, you didn't ask about it. Didn't even think about it. And I never thought about it. And there's probably a bad story associated with the whole "don't ask" thing. So, there's a fascinating story that has to do with world geopolitics, which enabled my mother to escape from Stalin's Soviet Union. But she didn't want to go. That's part of it, too. She wanted to stay. So, I do have a book in there. And by the way, my parents told me nothing. When my mother was getting on in years, I sat her down for a three-and-a-half-hour interview like this interview, and she finally told me many, many things that she had been keeping from me. Some things, she kept from me until her death. And by some coincidence, about five years ago, I began to research this. I was giving an invited talk at Dalhousie University in Nova Scotia. And to go to Nova Scotia from California is almost as far as going to London from New York because Halifax is four time zones away. So, the only way to get there is on a red-eye flight. I arrived there mid-day on a Sunday. And I asked the hotel clerk, "I have a few hours to kill. Is there something I can do here?" They said, "Why don't you try the immigration museum down at the harbor?"

And Halifax is not a very big town. You could just walk down to the harbor from the hotel. And I realized, "Oh, Halifax is exactly where my parents brought me from Europe when I was a baby.” And I went down there, and there was a very nice museum. And there was a feature of the museum where you could provide your name and other particulars, and they would find your immigration record. And the immigration record was like a census document. In the old days, when they took the census, they had a giant sheet of paper with columns, and everybody would get one row, and they'd fill in each column with age and stuff like that. And so, they had a document like that in the archives. And sure enough, a few weeks later, from Ottawa, Canada, I received an email with the records for all our family members. Four lines written in for our arrival in Canada. So that got me interested. I looked at the document I had at the bottom of a Safety Deposit Box, which was my mother's immigration visa. There was something incorrect on the immigration visa. That started a whole investigation. And for that, you have to wait for the book.

Zierler:

I'm sure your parents had trouble talking about it, but were they in camps, in ghettos, the woods?

Yablonovitch:

I'm glad you're asking because this is actually very interesting. By the way, relatively speaking, they did not experience that much hardship during World War II. But it's all relative. The reason they didn't tell me about it was not because they had harsh experiences, but rather because they had to falsify my mother's place of birth.

Zierler:

Who had to falsify it?

Yablonovitch:

My mother and father. In particular, my mother. She had to falsify her place of birth. And there's a story about that, which has to do with world geopolitics and one of the most important untold stories of the aftermath of World War II. But with regard to your specific question, my Father was a young man in Warsaw when the War broke out. The Germans came into Warsaw, and he quickly realized this was not good. And he went back to his hometown, which was about one hundred kilometers east of Warsaw, but which, nonetheless, was still ten kilometers west of the Molotov-Ribbentrop line. And so, he was still at risk because the Germans had control up to the Molotov-Ribbentrop line. My father died relatively young, and I didn't have the opportunity to interview him, but in overhearing his stories, he went those ten kilometers and crossed the Molotov-Ribbentrop line into the part that was controlled by Stalin. Maybe he had a relative there.

But he went there, and he awaited the Red Army, which was going to protect him. I had to overhear this story because he wouldn't tell me things. But I did overhear him tell his buddies the story that he waited, and waited, and waited for the Red Army to show up, and finally, they showed up with two soldiers and one donkey. He had already experienced the German occupation of Warsaw. And he realized the Red Army was not going to protect him, that they were hopeless. Then, he spoke a phrase, which I believe is an expression also in German, but it's almost the same words in Yiddish. He said what can be translated to, "The world became dark before my eyes." He saw the two soldiers and one donkey, and he realized they could not protect him from the German army A few months later, Stalin was establishing control over the eastern half of Poland, and my Father is an illegal immigrant because he went those ten kilometers.

So, Stalin rounds him up and sends him to the Gulag, which saved his life. Because what is the safest place during World War II? Well, the Gulag was not generally a safe place, but it was the furthest away from the war. He was in Arctic Russia near Arkhangelsk. Arkhangelsk was the Arctic seaport where some of the lend-lease supplies came in. And there's kind of a story in that part, too. But, basically, being in the Gulag saved his life. And then, Hitler double-crossed Stalin, and Stalin was in real trouble. He went to the British and said, "Look, you're Hitler's enemy, we're now Hitler's enemy. You should help us." And Winston Churchill said, "We'll help you. We'll even send you some lend-lease supplies. But you have to recognize the Polish government in exile in London." Stalin says, "Yes, anything you say." So, the Polish government in London says, "You have all these Polish people that you've sent to the Gulag. We want you to release them." So, my father was released from the Gulag after about three years. If you're in Northern Russia or Siberia, where would you go? You'd go south because it's very cold, right? But you don't want to go to the European part of Russia because it's occupied, and the war is raging. So, where do you go? The central Asian republics.

He essentially, became a free person working in a mine in the Central Asian Republics. In the first half of the War, he was in the Gulag. In the second half of the war, he was essentially a free person. My mother's story is somewhat similar. She was the daughter of a shoemaker. But he was slightly more than a shoemaker. He was a shoemaker with a very good reputation for having a good product. And so, he hired other shoemakers to help him make the product. So therefore, he was an exploiter-of-the-workers. But she had a college education, she became a schoolteacher, and she married the Principal of her school. And the Communist Party went to him and said, "Look, you're the leader of the school. You are obligated to join the Party." So, he joined. And then, when Hitler invaded Russia, the Party were beside themselves.

So, they said, "all Party members to the front." And my mother's first husband had no military training. He was sent to the front and was immediately killed. And so, my mother went from being the daughter of an exploiter of the workers to being the widow of a Party-member-hero overnight. And that gave her priority for evacuation. She was evacuated to Siberia and had the best job you could have during World War II. She managed the kitchen in one of the Gulags in Siberia, so she had food. And then, eventually, she went back to being a teacher. That's when she met my father. World War II was about to end. They got married.

Zierler:

What language did they speak to each other in initially? Yiddish?

Yablonovitch:

Yiddish, absolutely. And they ridiculed each other's knowledge of each other's national language. So, my mother, of course, ridiculed the bad Russian that my father spoke, and he ridiculed the bad Polish that she spoke.

Zierler:

Where were you born?

Yablonovitch:

I was actually conceived in Kazakhstan. I know you didn't ask that. And there's a story behind that as well. When they were released, they were free to move around, so they went to the Southern Asian Republics of the Soviet Union. You had Kazakhstan, Tajikistan, etc. Kazakhstan was the biggest, but Uzbekistan was the most important because it had the city of Tashkent. But I was conceived in Aktyubinsk, Kazakhstan, which you will not find on Google Maps because after Kazakhstan became an independent country, they decided to remove the Russian names from the cities and have more of their native names. And then, for geopolitical reasons, my parents managed to get out. They were given instructions by Israeli agents "Go to Vienna and give yourself up to the U.S. Army in the U.S. sector of Vienna." Vienna was divided in four like Berlin.

And then, the U.S. Army was obligated to treat them as refugees. They were sent to a former German Army barracks in a place called Puch, which was near Salzburg. And Salzburg was sort of the capital of the American sector of Austria. And I was born in that refugee camp near Puch. It was a Displaced Persons camp. And the conditions were very crowded. To give an idea, they had Army barracks, so they had a room that was roughly the size of a two-car garage, and each family got one corner of the two-car garage. And I was born in one corner of that garage.

Zierler:

What was your citizenship status?

Yablonovitch:

At that time, I was a Displaced Person. I never had a birth certificate. But the earliest document I have is a statement by a U.S. Army captain that I was present, I existed, and I think I was entitled to a ration coupon, which was a really big deal back then. You have to be aware of what was going on in Eurasia at that time. I was born in December of 1946. That winter was a very bad winter after very bad agricultural weather during the summer of 1946. And there was not enough food. Since I was being cared for by the U.S. Army, we had rations. But I remember my parents complaining about 1,600 calories a day, which actually isn't that bad because when I do calorie counting and try to lose weight, it's 1,500. But I do lose weight. At 1,600 calories a day, you can't work strenuously. You still lose weight at 1,600 calories a day.

So that was the circumstance, and this is what's going to end up in the book, how I ended up in Canada. The U.S. Army was getting tired of running these camps, and they were trying to get everybody out. At first, when we arrived in that camp, many of the Jews were trying to get to Israel. And it was not possible to get to Israel because of the British naval blockade. But what happened during that period of time was that there were Israeli terrorists who were basically assassinating British soldiers. And the British, during that period of 1946, they got very tired of Israel and the Jews. They thought, at first, they could hold onto Palestine as a colony, and they were still preventing the Jews from getting to Israel. But they would try to sneak in. Very few ships got through by May of 1946. By then, my mother was pregnant with me. To assist the blockade, the British policy changed: "Let's give these Jews a better deal than going to Israel."

And so, they went around to the various British Commonwealth countries. They went to New Zealand and said, "You have a quota. You take 10,000. Australia, you take 30,000. Canada, you take 50,000 or 60,000. We'll take 80,000 in the UK." France took 80,000. And they managed to distribute the Polish survivors of the Holocaust. So how did the Polish Jews survive the Holocaust? If you were in Poland, you had little chance of surviving. So, most of the survivors survived the way my father did, by absconding to the Soviet Union. Those represented about 10% of the Polish Jewish pre-War population, the total of which was about three million people. And so, there were about 300,000 Jews that Stalin held until spring of 1946, and then he was obligated by the agreements made at Yalta to send them back to Poland. Many of those Jews ended up in Displaced Persons camps. And there were also Polish-Jewish survivors of the death camps. But most of the survivors actually were never in the death camps. Like my parents they survived because they were in the Soviet Union.

Zierler:

Do you have any memories of Europe?

Yablonovitch:

None at all. So, I grew up in Canada thinking I was Canadian. My parents spoke to me in Yiddish until I was about five years old. And then, they sent me out onto the street, and I played with the other kids, and I quickly adopted English. At that age, you can learn a language almost instantaneously. Between the ages of four and six, children learn two words every day. And so, I learned English, roughly at age five, outside, playing with other kids.

Zierler:

And you thought you were Canadian. When did your parents tell you the real story?

Yablonovitch:

No, they told me I was born in Europe, but they didn't tell me anything about the circumstances. And my attitude was that, "I speak English. My parents speak very bad English. I've adapted. I have friends." My poor parents understand nothing. I understood everything. So, I had this feeling that, "I don't need to know anything about the old place because I'm fully adapted to Canada. I speak the language, etc."

Zierler:

Were you Jewishly connected at all growing up? Were you members of a shul? Were you bar mitzvahed?

Yablonovitch:

Yes, I was bar mitzvahed, and the first two years of my education was in a parochial school. Actually, if you include kindergarten, three years. And then, they moved, and they sent me to a regular English-speaking school. You had a whole issue in Montreal between the French and the English. That was a whole other issue. Where are you from?

Zierler:

I'm from New York.

Yablonovitch:

So, there was a Jewish culture in Montreal that some say, was richer and better than the New York Jewish culture.

Zierler:

That's what I've heard Montreal Jews say, yes.

Yablonovitch:

Now, if you want to understand the culture, there's a movie you can watch. But I don't even think you can buy the disc. But it garnered an Academy Award nomination; it was a really good movie. It was called The Apprenticeship of Duddy Kravitz. And we should watch it together, so I can point out to you what's going on. It has the three cultures in it, and it reproduces a moment in time that lasted quite a long, until about 1970.

Zierler:

What were your dad's job prospects when he got to Canada?

Yablonovitch:

Well, the British were very eager to make sure that they would not go to Israel because they still wanted to retain it as a colony. So, he was given a terrific deal. He had an apartment waiting for him, he had a job waiting for him. But the most important thing, he had legal papers waiting for him. You see, from 1939 until the time we entered Canada, which was 1948, for that nine-year period, he had no papers. He was undocumented. Which meant that wherever he was, the local dictator could do anything to him. So, he was very, very politically insecure. And the deal that the British offered included legal papers. And that was the most influential factor. Most refugees wanted to immigrate to the United States, but Truman could negotiate with Congress a quota of only 12,000 Jewish refugees per year. So, for those 300,000 surviving Jews, it would have taken twenty, thirty years for them to get out of the camps. And they were all eager to get out of the Displaced Persons camps due to the crowding. And the Army was eager to close the camps.

When I finally interviewed my mother in her old age, she said that she was given a choice by the authorities. The choices were Canada or Argentina. And I'm very grateful, of course, she chose Canada. The education system is very good, I was extremely well-prepared. And by the time I was in graduate school at Harvard, I had already taken all those graduate classes. So, I was acing the courses. They thought I was pretty good. But I was acing everything because of the wonderful education system in Canada.

Now, there's another peculiar feature of the education system in Quebec, which was controlled by the French-Canadian majority. Many were farmers at that point in time. Most people were farmers, even in America up until about 1900. The Quebeckers just didn't see the point of keeping kids in school, when they could be helping out on the farm. They decreed, "High school is complete at grade eleven." So High School finished at grade eleven, and then I went straight into college. I was sixteen when I got to College, and I was twenty when I got into Graduate School. But I skipped no grades. It was just the educational system in Quebec.

Zierler:

We're a half an hour in, and we can talk about science now. We're doing great. We have covered a lot of ground in thirty minutes.

Yablonovitch:

You've just been given the brief overview. We haven't even gotten into the world geopolitics. So, for that, we have to do the geopolitics offline. I don't want to take away any more time.

Zierler:

Well, let's develop the narrative that leads to your career. So, the first question there is, when did you start to get interested in science?

Yablonovitch:

I started to get interested in science with Sputnik. And I remember the autumn of 1957. The Hungarian Rebellion was a year earlier in '56. So, a year later, Sputnik was launched. I'm in the living room of my house, my parents had some of their friends over, and they're talking in a very worried manner among one another about Sputnik. And I'm a kid, maybe ten years old, and I'm playing with toys, little tin soldiers or whatever. And I'm overhearing my parents talk. "This is very worrisome. What's going to happen?" Because they are escapees from the Soviet Union.

So, they were a little worried about the implications and so forth. And that's when I first got the idea that science was powerful, and that maybe I should become interested in it. And I would say from that point on, I was interested in science, I was interested in electrical circuits, I had hobbies. And, of course, we had this fantastic resource, the Amateur Scientist column in Scientific American. I had a good friend who was also interested in Science. We tried to duplicate some of those projects. We would raid abandoned buildings for the wiring to do experiments, and it went on from there.

Zierler:

Of course, in the Canadian system, you go into undergraduate knowing what you're going to major in because it's modeled after the British system.

Yablonovitch:

Actually, that's not quite the case. It's modeled more after the American system. And so, I did enter with the thought that I would Major in chemistry because I was fascinated by it.

Zierler:

But you don't have to declare the major as a freshman?

Yablonovitch:

Yes. In fact, what happened is, my freshman chemistry class was taught by a theoretical chemist. I was sixteen years old. And he thought that the most important thing was to teach the fundamentals. So, he started with Schrödinger's equation. And what happened was, my mind was kind of logical and sequential. You cannot absorb Schrödinger's equation at age sixteen with only a High School education. So, my mind absolutely rebelled, and in the British system, the grade is out of one hundred. It's not A, B, C, D. And I got a fifty-three out of one hundred in chemistry. And they absolutely would not let me major in chemistry. They said, "Your grade is too low. You cannot major in Chemistry."

So, at the end of my freshman year, I went to the Physics department with my tail between my legs, and I said, "I'm sorry, I have terrible grades in chemistry, but I did okay in Physics. Would you let me Major in Physics?" Now, the Majoring was not a preferred avenue. The goal was to Honor in Physics. That's a British thing. Honoring is, like, a step beyond Majoring. So, the Department's attitude was, "Well, if you could possibly make it, sure, go ahead, give it a try." And so, I entered the Honors program in my sophomore year. I had already taken to Physics very well as a freshman, and from that point on, I was taking classes restricted to Honors candidates. And so, I was immediately given the best Physics training I could have.

Zierler:

Was your sense as a Canadian kid that McGill was the end-all, be-all for undergraduates?

Yablonovitch:

Yes, absolutely. Everything revolved around McGill. It seemed that every professional person, Doctor, Lawyer, etc., had been trained at McGill. It certainly was an outstanding education. The thought of going to an American college never crossed anybody's mind. No matter how wealthy or upper class you were, it would be extraordinarily unlikely that you would apply to an Ivy League school, for example.

Zierler:

Graduating in 1967 is relatively early, but I wonder if the counterculture reached McGill during your time as an undergraduate.

Yablonovitch:

Absolutely. Even when I graduated from high school, it was all about Bob Dylan and so forth.

Zierler:

Were there Americans who were dodging the Vietnam draft? Is that something that you were aware of?

Yablonovitch:

Not in '63. Because I entered McGill in '63. That was a little too early. But McGill always attracted quite a few Americans because it was good and inexpensive. Basically, the Americans paid so-called "in-state tuition" at that time. And so, it was a good deal for Americans to go there.

Zierler:

Who were some of the professors at McGill who were influential in your intellectual development?

Yablonovitch:

Well, some of them are still alive, and I've met them in recent years. But the most influential was a high energy experimentalist by the name of Doug Stairs. He taught me two of my classes, maybe three. He was wonderful. And I'd hate to start naming names because I'll get the names wrong, and I'll forget some of them, but they were quite wonderful.

Zierler:

And for you, it was always experimentation? Did you ever flirt with theory?

Yablonovitch:

Not really. I'll tell you a couple of stories that are interesting from the Physics viewpoint. I was taking Electromagnetics, and that was a sophomore course. And you learn the basics of electricity and magnetism. And one morning, three professors show up. Not just one, three. And they have very somber looks on their faces. And the usual Instructor says, "Students, we're going to have a special class today because one of our colleagues has passed away. We're going to tell you about him." So, they had a special class, talking about his pedigree. So basically, our Professor says, "Well, he taught me Electromagnetics, and he learned it from somebody else, who learned it directly from Maxwell. And we're handing it to you."

Zierler:

This is dor l'dor, generation to generation.

Yablonovitch:

Oh yeah, right, right. Yeah, so it absolutely was generation to generation. And you could almost call physics a substitute religion. In fact, that's certainly the way I felt because physics was answering the big questions that religion was always trying to answer. "Where did we come from? How did the world begin?" Physics answers all those questions. So, it was definitely a competitor to religion. I have great respect for religion, but the reality is that physics was a competitor. That was the most interesting event in my sophomore year. Then, in my junior year, we had relativity and the first course in quantum mechanics. Relativity was already filled with enough paradoxes, but nothing compared to quantum mechanics. So then, you get the idea that, "Oh, my, Physics is filled with paradoxes. This is now beyond a competitor to religion. This is now filled with things that are very hard to understand."

That was a major influence. In one year, my junior year, I was inducted into relativity and quantum mechanics. And then, I realized, "There's something really going on." Then, I had to do my final exams at the end of my junior year. And I was sitting in the library. And I'm kind of a lazy person, and I just couldn't bring myself to study. So, I was glancing at the shelves, and there were these red books on the shelves. Now, let's place the year. I finished my freshman year in '64. That means my sophomore year, I would've finished in '65. And my junior year, I would've finished in '66. So, what do you think was on the shelf in 1966? The Feynman Lectures! They had just arrived on the shelf, only volumes one and two.

What happened, is that instead of studying for my final exams, I cracked open the Feynman lectures. And the volume was still kind of fresh because I was one of the first people to look at that book. And I just couldn't put it down. And so, I read volume one pretty much cover to cover, maybe a good part of volume two. You could not have a better preparation for your final exams, so I ended up doing quite well. And then, the same thing happened in my senior year. By then, probably volume three was available. I just read through them all. So again, you couldn't ask for a better preparation for your final exams.

Zierler:

What lab work or even summer internships were really important to you as an undergraduate?

Yablonovitch:

My first physics job was after my junior year. It was at the university, a nuclear physics job. And my job was to make amplifiers for the nuclear instruments, electrical amplifiers. And the professor, at the beginning of the summer of 1966, throws two transistors on my workbench. He says, "There's this new thing called the MOS transistor. Why don't you make an amplifier that we can use?" That was my summer project.

Zierler:

Tall order.

Yablonovitch:

Well, it was a two-transistor amplifier, it was not that big a deal. But we hadn't learned about MOS transistors. We'd learned about bipolar, but not MOS. But as he threw the two transistors on my workbench, he said, "By the way, be careful. They say they're very sensitive to electrostatic discharge. And so, I started working, and the first thing I did was to wreck the first transistor. Because I took no electrostatic precautions. I paid no attention to the warning. And to put it into context, in those days, you bought individual transistors. The integrated circuit already existed, but you still tended to make circuits out of individual transistors. The individual transistors probably cost fifty dollars each in 1966 dollars. So, in today's money, that would be about ten times higher. So, I wrecked something that cost $600 as a summer student. And of course, I always wanted to be an experimentalist. That is also what attracted me to chemistry, you mixed chemicals or heated things up.

That's what happened in the summer of my junior year. Then, in the autumn of my senior year, Professor Stairs, again, calls a meeting of all the top students who were Honoring in physics. And he said, "By the way, you students are now expected to apply to graduate school. The deadline is coming up." And we looked at each other and said, "What's graduate school?" And he explains it to us, and he says, "There's a process. And you have to choose the sub-field of Physics and apply according to which university is good in that sub-field." So, he runs through the sub-fields of physics, which are not that different from today, and he gets to theoretical physics. And everybody raises their hand and says, "Yes, we want to go into theoretical physics." Except me, I don't raise my hand. And so, he says, "This won't do. You can't all go into theoretical physics. That's crazy." And he says, "Let's try this again." And again, everybody but me raises their hand for theoretical physics.

So, he says, "Look, most of you are going to be experimentalists. Let's face it. Look at it this way. If you're an experimentalist, you get to play with very expensive toys, and you can still do paper and pencil theory, if you want. But if you go into theoretical physics, you'll just end up programming computers, and that's not as much fun." So that changes quite a few minds. And so, everybody is told where to apply. What happens then is that we were appointed advisors for our sub-field. So, I applied to twelve American universities. You have to understand the situation. We were told that no one will take our PhD degree seriously unless it's from a top American university.

Zierler:

This is a much different purview than when you were in high school, and culturally, American schools were not even on your radar, no matter your social class.

Yablonovitch:

Right. But this is different now. Now, it's Physics. And you have to get realistic about the professional situation in Physics. Academically, no one's going to take your PhD seriously unless it's from an American university. So, we were all expected to apply to American universities.

Zierler:

So, McMaster, Toronto, you didn't even bother?

Yablonovitch:

They were good places, but at that time, we were told to apply to American universities. So, we applied to American universities. Part of the reason I managed to get into Honors Physics is that it was the period of time where students could flunk out. There was little risk to the department. If you couldn't hack it, you would flunk. And today, of course, we don't flunk people. We just sort of help them out as best we can. There was no grade inflation in those days. They didn't care if you were unqualified. "If you want to go into Honors Physics, fine. But if you're not going to make it, you'll flunk out, you'll do something else." The survivors of Honors Physics at McGill were about fourteen students, with whom I became very close to because we took all of the advanced Physics classes together. Now, the part of the system that was British is, if you're Honoring in a field, you took nothing else. It was all Physics and Math. I would've liked a little bit of history, a little bit of culture. None of that.

Zierler:

But as you say, when you got to Harvard, you were pretty well-prepared.

Yablonovitch:

I was pretty well-prepared though, yes. So, what happened is, my assigned McGill advisor was a theoretical solid-state physicist. He asked "Well, where'd you get in?" I said, "I got in wherever I applied." So, he looked at all the Universities. In those days, you didn't have the internet, but you had the Directory of the American Physical Society. He looked up the Harvard Physics and Applied Physics Professors. And he said, "You've got to go to Harvard. You have a professor you want to work with, and you should have a backup. So, at Harvard, you want to go work with Bloembergen, and your backup is going to be Michael Tinkham."

Zierler:

And this was going to be in the physics department proper or EE? Or what was the breakup at that point?

Yablonovitch:

Harvard did not have EE. It has to do with the history of Harvard. There was a bequest for a School of Mechanical Engineering from one of the pioneers of the American Industrial Revolution, a great inventor, the founder of the United Shoe Machinery Company, Gordon McKay. And he left a very, very large bequest because he was one of the wealthiest men in the United States. And there's a long story of how it ended up being a small department after the large bequest. Finally, Harvard convinced a judge that what was understood to be Mechanical Engineering in the 1800s was, in the middle of the twentieth century, Applied Physics. Harvard took all the fields that were somewhat applied out of the Physics Department, and they put them into Applied Physics to take advantage of the bequest. At that time, it was called the Division of Engineering and Applied Physics. Most of the Condensed Matter Physics was there. So that's how it worked out. And I was told to go to Harvard and seek out Bloembergen as my thesis advisor. It was pretty good advice because he ended up being a Nobel laureate. And Tinkham was very good, also. He was a very outstanding scientist. I took a couple classes with him. He was great.

Zierler:

Were they contemporaries?

Yablonovitch:

They were pretty close, yeah. And Tinkham was in a different field. He was in superconductivity, but it was condensed matter. The faculty who were slightly applied, were in the Engineering Division, but they were friendly with the Physics Department.

Zierler:

Did you sense a hierarchy there as well, that they were at a lower level than the theorists because of the administrative divide?

Yablonovitch:

No, the social hierarchy was, who had tenure and who did not have tenure? That was the main social hierarchy. Didn't matter whether you were pure or applied physics. But you're actually right, in that period of time, pure Physics looked down on Engineering.

Zierler:

Sure. Squalid state.

Yablonovitch:

Squalid state, you got it. One more interesting thing happened as I had already been accepted into graduate school in March or April 1967. In May, the McGill department chairman came to some of us students, and he said, "There's a physics contest being held among the different universities in Canada," A Canadian Association of Physics contest". It was contest between departments, but the students were supposed to take a national exam for bragging rights of which was the best physics department in Canada. The reaction among the students was "I'm already going to graduate school. Why am I doing this?" Well, because the chairman asked us. "Okay, fine." All the students did it for the same reason. So, I took the exam, and a few weeks later, I was presented with a letter from the department. "Congratulations." I came in second in Canada. Well, I had a certain advantage. I was one of the first students to read the Feynman Lectures book.

So, I had a definite advantage. But I didn't think much of it. Coming in second, let's face it, it's second, right? So, I gave the letter to my mother, who left it at the bottom of a dresser drawer, where it sat for the next twenty-five or thirty years. And I'd forgotten about the whole thing. Years later, I'm writing a paper on an artificial way to create Hawking radiation. I'm not a field theorist, but nonetheless I'm writing it. And what happens is that I'm warned there's a mistake in my derivation. This is now twenty-five years after McGill. I'm using nonlinear optics to create Hawking radiation. And I'm told, "Look, I think there's a mistake in your math here. Why don't you call Bill Unruh at the University of British Columbia? And so, I call him up, and he understands what I'm doing right away. Within five minutes, I correct the math error, and I submit my paper. It gets accepted. And later that year, we were supposed to invite distinguished speakers to Bell Communications Research, and there would be a significant honorarium.

So, I said, "I know the exact person because he explained to me all about this problem in field theory. He explained it to me in five minutes. So, he's very good at explaining. He's a great speaker, and his expertise is in gravity." So, to calibrate him, Hawking radiation is sometimes called Hawking-Unruh radiation. And he was Mr. Unruh. So, I invite him to be a speaker, and so he says, "Okay, fine." Then I found out, " Because of the honorarium, the company requires that I submit your résumé with the paperwork." So, he says, "Okay," and he sends me his résumé. And I look at the résumé, and I see that he is a University of Manitoba, graduate, 1967, same year as me. And among his honors, he won first place in the Canadian Association of Physicists contest. But that made no impression on me, but by some coincidence, I was visiting my mother a week later. And my mother says, "Look, I'm going to die soon. You should take all your papers out of here and store them safely."

So, among the papers is a letter saying, "You came in second in the Canadian Association of Physicists contest." I reacted, "Oh my God. I came in second to Bill Unruh." So, this is not bad at all. Then, he shows up to give the lecture with a big honorarium, and I say, "By the way, I noticed on your résumé that you came in first. By the way, it's not a big deal, but I came in second." And sure enough, he gave a totally wonderful lecture. And everybody in the company attended. So, the scientists went, but the secretaries went, as well. And the secretaries were sitting in the front row. To tell you how good the lecture was, it was a lecture on General Relativity, answering why it was very hard to get a unified theory of gravity and quantum mechanics. The secretaries who were sitting in the front row heard the lecture, and then afterward, I went up to them and asked, "Did you get much out of that?" And they said, "Yes, we understood every word." And that's how good a lecturer Bill Unruh is.

Zierler:

That's great. I'm glad we diverted from the chronology there. I'm glad we got that in. That's very special.

Yablonovitch:

And you can see the series of unlikely coincidences. That I had totally forgotten about the whole thing. If it weren't for my mother being like that and saying, "Well, I'm going to die soon, so you better take your stuff," I wouldn't have known. She didn't die soon; she lived many years after that. But I collected my documents, my diplomas, award letters, all that stuff.

Zierler:

Back to Harvard, given the two choices you had for advisors, it wasn't just advisors but fields of study for you. So how did that play out?

Yablonovitch:

Well, I had great admiration for both of them. The problem with superconductivity is, it's more of an academic subject. Whereas lasers worked at room temperature. Superconductivity needed low temperatures. Lasers worked at room temperature, could be practical, and so forth. And I really liked the idea that I was in Applied Physics and not in Physics. And so, I think that was a factor. Honestly, I would've done it the other way if it had been recommended in the opposite direction. I was still going by the advice of my advisor from McGill.

Zierler:

That's what you did?

Yablonovitch:

So, I ended up doing what he said, yeah.

Zierler:

What was the coursework, being in Applied Physics but also having that close affiliation to Physics?

Yablonovitch:

You have to understand, the Solid-State Physics at Harvard was mostly in Applied Physics. The coursework was fabulous. Tinkham was just great. I had two classes from Tinkham. I learned nonlinear optics and lasers from Bloembergen. It was a fantastic education. I audited Coleman teaching relativistic quantum mechanics. These are legendary instructors. I had Glashow teach me electromagnetics. That was a repeat of what I had taken as an undergraduate. He was bored with the subject, but I was also bored with the subject. He tried to fill it with all sorts of weird stuff, like how does the earth generate its magnetic field? Which at that time was still very controversial. So, I had just wonderful instructors.

Zierler:

And in optics specifically and solid state more generally, was your sense as a graduate student that theory was driving experiment, or that experiment was driving theory at that time?

Yablonovitch:

The theory was a handmaiden to experiment. Discoveries were made. Let me remind you some of the discoveries that were made. Charles Townes invents the laser. He was an experimentalist, but he understood theory. Otherwise, he never would've thought of the laser. So, he understood theory very well. And the same is true about Bloembergen, who's known for his great experimental work, but he also did some theoretical work, wrote books and stuff. So, I wanted to be like them, an experimentalist who happens to know some theory. And then, in the experimental work, I restricted it even more. At the end of the day, it should be something that helps humanity. And mostly, I was thinking in economic terms. Today, we would say, "You want to help humanity, do something in the physics of medicine." But in those days, it was a little bit more toward things that are financially good or to create great industries.

Zierler:

What was the process for you putting together thesis research?

Yablonovitch:

Well, you bring up an interesting question. A difficulty existed in my early years of research, until about seven years after my PhD: I always seemed to be doing projects that other people wanted me to do. Occasionally, I would go off on my own. My first assigned project was what's today called four-wave mixing. The four-wave mixing was like a type of Raman spectroscopy. And you end up seeing the spin flips in InSb. InSb is a very interesting semiconductor. So, I was given that as a task, and I had many false starts. I was just a wild experimentalist starting out, because I had already done Science Fair projects. I didn't tell you about my Science Fair experience. My last year of High School, I entered the Montreal Science Fair, and I made an instrument called the Polarograph that was described in the Amateur Scientist column of Scientific American. I made a Polarograph. The device was basically an electrochemical instrument. It's actually a great analytical instrument. You can buy them commercially. It worked by measuring the IV curve of a solution. So, I had to make a box that measured the current versus voltage.

I was familiar with experimental work, beginning from that project. When it came to the Science Fair, there were about one hundred entries from the whole Montreal region, and four of the one hundred entries were Polarographs. But mine was the only one where the experiment really worked. And I'll tell you how the judges knew the experiment worked. You have to picture the year, the spring of 1963, so it's quite a long while ago. And they bring in scientists from various organizations in Montreal, mostly companies, to be the judges. And there was an IV curve, and it was supposed to have an upward slope. The IV curve of professional instrument is supposed to have an upward slope, and a plateau, and then a further upward slope. The plateau, the height and width, were very important for determining analyzing a solution. But there was a problem. The current went down at a certain voltage, negative resistance. And I felt extremely uncomfortable. But it was reproducible, though very hard to understand.

And so, I did my best to insert error bars, but the curve still went down. And then, the judge comes up and says, "Why is that going down?" And I kind of explained everything, but I couldn't explain why it was going down. And he said, "Mine does the same thing. And I don't know why." So he was, apparently, a scientist who had one of these electrochemical instruments, and he recognized that it was real data because it went down, and it isn't supposed to go down. It had a dip, a brief section of negative resistance. Now, I looked at my competitors, the other three, and none of their data made any sense at all. They had IV curves that were all over the place; their data was bogus. So, we ended up winning first place in chemistry, not overall first place. And the prize was three hundred dollars split between me and my partner. That was actually a lot of money back then. And my father was floored. Because the one hundred and fifty dollars was approximately two weeks' salary on his part. And so, he suddenly realized, "Oh, who is my kid?" By then, he was suffering from heart disease, and he was in the hospital. And he would discuss with his other friends who were also suffering from heart disease in the hospital. And he said, "Well, my son just got into Harvard." And his fellow patient says, "Harvard, that's where President Kennedy went." So that was a very big deal to him at that time. My father didn't understand President Kennedy went there as an undergraduate. A different social class from the graduate students.

Zierler:

Back to the thesis research, what did you see as your contributions as you were putting this together?

Yablonovitch:

I did this work on the four-wave mixing, the spin flip. And I had many false starts. I bought a lot of equipment that ended not being used. And it took me twelve months. I went to Professor Bloembergen, and I said to him, "Please accept my apology, it has taken me twelve months to do this. I had a lot of false starts, I wasted a lot of time, I wasted a lot of money on equipment I didn't need. Please forgive me." And his reply was, "You have data? You have data, and you've only been here for twelve months?" And so, he snatches the data out of my hands, he looks at it, and he could exactly see the spin flip response. And so, he immediately developed a very high opinion of me because he was so flabbergasted that I had data so quickly. And then, he left me on my own. "Do whatever you want." Which was great.

Zierler:

And you did well by that, not having that sort of more intensive mentoring?

Yablonovitch:

Well, what happened is that the whole early part of my career was a conflict between people telling me what to do because it's supposed to be good for me versus just pursuing my own ideas. And it was extremely frustrating, and I'm going to tell you more examples of that. But this is a counter example because he left me on my own. And I said, "Well, let me make a better version of the CO₂ lasers." I made a pulsed version, which was called a TEA-laser at that time. And I already had all the optical equipment from the prior experiment. And I could focus the laser pulse and create the loudest, brightest spark you could imagine in mid-air. And I said to myself, "This is amazing. You're creating a spark, and there's no wires, no electrodes, nothing. You're just creating it in air." And then, there was huge amounts to study. You can do it in different gases. You can do it in different transparent materials. So then, I took a whole different line on my PhD thesis. I just put different materials at the focus of that laser and looked at, what is the threshold for causing breakdown? So, it was the beginning of high-field, high-power, laser physics, which became a very big field later on. That became another part of my PhD thesis.

Zierler:

When did you have enough data to know that you were ready to defend?

Yablonovitch:

Well, I kept doing more stuff. Basically, people expect you to stay there for five years, so I stayed there for five years. And I got three different projects done, each one of which, looking back, could've been a PhD thesis.

Zierler:

Was there anything particular that wound them together to signify what you were interested in?

Yablonovitch:

No, the only thing that wound them together is they all relied upon the CO₂ laser, but only the one that involved laser breakdown required the high-power laser. So, I became quite interested in high powered lasers, plasma formation, and so forth.

Zierler:

Who was on your thesis committee?

Yablonovitch:

Well, I'm not one hundred percent certain. But I think it was most likely Peter Pershan. It could also have been Henry Ehrenreich. It only required three people. And the only person who asked questions was Bloembergen, who asked a very good question at the thesis defense. So, the work was quite diverse. In the final Spring before I graduated, I wrote up two papers, both of which were submitted to Phys. Rev. Letters. And I remember, when it came time to edit the papers, it was already summer, and Bloembergen wasn't coming into campus. To edit them, I had to go to his home. So, I drove out to his home, and we edited the papers very quickly. And we sent them off for publication. And then, when I started my first job at Bell Labs, about a month after I showed up, the two papers appeared in print in Physical Review Letters. And the other scientists at Bell Labs were in awe of me. "He's just shown up, and he's already got two Phys. Rev. Letters." And that was the big thing back then. The journal Nature was nothing back then. Phys. Rev. Letters was the place to publish the good stuff.

Zierler:

Did you have Bell Labs wrapped up before you defended? Were you all set to go?

Yablonovitch:

Yes. So, this is roughly how it worked. Bell Labs had a recruiter who was a former Harvard graduate. So, they'd send the Harvard graduate back to Harvard, who would ask the Professors, "Do you have any hot young prospects?" And they'd say, "Well, why don't you go interview so-and-so?" So, he came to me and said, "Would you like to come out for an interview?" So, I said yes. So that interview was quite an experience. You've probably heard about the Bell Labs interviews.

Zierler:

But this is a real job. You skipped the postdoc thing altogether.

Yablonovitch:

Not exactly. So, I have to tell you what the interview was like. You may have heard this from other people who were at Bell Labs. I'm giving my interview talk on the part having to do with the laser breakdown, and I started my talk, and ten minutes into my talk, there was a notorious scientist there by the name of Phil Platzman. And he interrupts my talk after ten minutes. And he says, "Everything you're saying is wrong because of such and such." And I say, "Well, I can really understand how it looks that way, but it's actually okay." And then, he interrupts me again, and I reply, once again- I'm on a job interview- very politely. And then, he interrupts me a third time, and he says, "Everything is wrong because of thus-and-such." And I reply, "As anyone who has read the famous paper by Keldysh would know, this is actually correct." It was something like that. So, I had gotten back at him by implying that he hadn't read the famous paper by Keldysh. Have you heard of the Franz-Keldysh Effect?

Zierler:

I have not.

Yablonovitch:

He was one of the greatest, if not the greatest, solid state theorist in the Soviet Union. And he was trapped in the Soviet Union, they would not let him leave. This was during the Cold War. In my interview, as soon as I put Phil Platzman in his place, all the Bell Labs managers who were interviewing me, respected me, and they all wanted to hire me. Because I stood up to Phil Platzman. And so, I had a job waiting for me. That was in March before June graduation.

Zierler:

So, this was a hybrid post-doc member of technical staff?

Yablonovitch:

It wasn't quite like that. Because I was Canadian, they could not hire me in a normal staff position. So, they said, "Well, we'll hire you as a postdoc, but we can assure you, we're going to go through the immigration process, and we'll convert you to a Staff Position." And I took them at their word, and they did that.

Zierler:

Before Bell Labs came together for you, did you feel like you were on a normal academic trajectory where you would do a post-doc and get an academic job? Or was Bell Labs always a goal for you once you understood what you wanted to do?

Yablonovitch:

No, Bell Labs was not a goal. In fact, being a Professor was not a goal. I wanted to go into industry and create things that would be for the betterment of humanity.

Zierler:

Like John Fan.

Yablonovitch:

Yeah, John Fan says that, yes. He was my classmate. So that was my intention, and my interviews were entirely industrial interviews. I think I might've had one academic interview, but they weren't interested in me, and I wasn't interested in them. So, what happened is, I had these job interviews, and I went to one of the other Professors, and I said, "Well, I've got all these jobs." Every place I interviewed wanted to hire me. "So where should I go?" And he said, "Well, you have to go to Bell Labs. It's the absolute best place." I didn't know that was the prevailing attitude at the time. And so, I just listened to him, and I went to Bell Labs. And it was not a difficult decision because I walked down the corridors during my interview at Bell Labs, and I saw the nameplates on the doors. And the nameplates were the citations in my thesis. I said, "Wow, all these people that did all this work that I needed for my PhD thesis, and they're on the doors here, including some very famous people." Then I understood at that point, that Bell Labs was the place to go. Bell Labs had other benefits. You didn't have to write proposals, you had unlimited funding, and so on, and so forth. So, I got to see some of the good parts, but there were also some bad parts to Bell Labs as well.

Zierler:

Such as what?

Yablonovitch:

The utter irrelevance of the research, which I later understood arose for legal reasons, that Bell Labs had all its patents taken away in 1956. And so, they were supporting every crazy thing, and they were doing all sorts of nutty stuff that had no applications.

Zierler:

So, you're saying that the research was too basic.

Yablonovitch:

Oh, yes, by far, for me. Because I wanted to have an impact, and they just wanted to rack up papers in prestigious publications.

Zierler:

What group did you end up joining?

Yablonovitch:

Well, I joined the laser group, so I had some pretty famous bosses. The person who actually hired me was Kumar Patel. And then, he handed me off to Bill Brinkman. So, I had a couple of pretty famous bosses.

Zierler:

Are masers totally out at this point? Are they still being used?

Yablonovitch:

Masers did not make the cut of history. In other words, they were very important scientifically in that they led to lasers. I think they're still used in radio astronomy. That's not a small thing. And why they're used in radio astronomy is because they're slightly lower noise than other amplifiers.

Zierler:

But at Bell Labs, you're in a totally laser environment?

Yablonovitch:

Yeah, it was a laser environment, and I got there in 1972. And to put it into historical context, in 1967, optical communication was proposed by a scientist, Charles Kao, who was working at the Standard Telecommunications Laboratory in England. And he proposed optical communication, and by January 1 of 1970, it was published that optical fiber attenuation in s was low enough to be interesting for long-distance telecommunications. Corning announced in Jan. 1970 that the optical attenuation was twenty decibels per kilometer. They regarded that as fantastic. Today, we have 0.1 decibels per kilometer. But twenty decibels per kilometer was already low enough to launch the industry. So, Bell Labs had made an executive decision at that point to put huge efforts toward making optical communication practical. There was a post-Vietnam War recession, and they weren't able to hire until my recruitment year, 1972. I was one of the first new people they hired to work in optical communication. The people who were already there, had already started working in optical communication as well.

Zierler:

What's a great example to illustrate this point where you were frustrated that you had real interests in the applied world, but Bell Labs was just too basic for you? What would be a good example of that?

Yablonovitch:

Well, I'll give you something concrete. I had some friendly Engineers my age, with whom I used to go motorcycling and having fun. And if I tried to learn how the phone system really worked, it was a big secret. You couldn't actually figure it out. And there was a reason why it was secret. Because somebody had discovered a publication in the Bell Labs Technical Journal that revealed the long-distance tones, and some shady people started creating these things called blue boxes that would enable you to make free long-distance calls. So, they absolutely did not want their scientists learning how the phone system worked. "Just go off and do your science." It turned out that the guy I was motorcycling with was a normal Engineer, and he would tell me the technological facts. If it weren't for that, I would have no clue how the phone system worked. He would tell me what he was doing. He still didn't tell me the secret of the blue box. So that was an example of the frustration.

Zierler:

What did you end up working on?

Yablonovitch:

Well, I ended up continuing with my CO₂ laser work, under the following motivations. The year of 1972, in which I was recruited to Bell Labs, in which I published two papers in Phys. Rev. Letters, I graduated, and whatever else happened that year, there's another very important event that happened. I went to what was then called the International Quantum Electronics Conference, which is, today, absorbed into CLEO. And they had an invited speaker, Edward Teller. In the biggest hall of the hotel, by coincidence in Montreal, I found myself in the back row of an audience of 2,000 people listening to Edward Teller. And the crux of what Edward Teller was saying was, "Well, we're going to have laser fusion energy. And we're going to do it with lasers, we're going to create plasmas, and this is going to be the most superior form of energy out there."

And I was just a fresh graduate, and I'm sitting in the back row. I said, "Wow, he must know what he's talking about. He's Edward Teller. What have I done for my PhD thesis? I made all these laser plasmas. I made all these sparks. So, this would be a good field for me to get into." So, I got into it. And of course, at Bell Labs, they said, "Anything you want to do. You want to do astrophysics, do astrophysics. Just don't try to learn how the phone system works. "So, I went off in that direction, and I used the plasma sparks to make very short CO₂ laser pulses. That was a big deal. Making short pulses was a big deal in those days. And I began my venture into laser plasmas, which were supposed to be applied toward laser fusion energy. So, what happened, about two years later, Bloembergen meets me and says, "Would you consider coming back to Harvard as an Assistant Professor?" And I said, "Yes. Absolutely." And so, I became an Assistant Professor, and I continued the research.

Zierler:

Of course, you know you're giving up a full-time real job for a very tenuous position

Yablonovitch:

I didn't think of it that way at all because I had succeeded at everything, and I had assumed that I would get tenure.

Zierler:

But surely you knew that the culture at Harvard was the opposite of that.

Yablonovitch:

People told me that after I had already accepted the job, and I said to myself, "That does not apply to me."

Zierler:

This was well-before Howard Georgi. Who had done it before?

Yablonovitch:

Well, let me put it this way. Why do you take young people and send them into war? Because they believe they're indestructible.

Zierler:

Just clarifying that there wasn't a specific precedent that you were going on here.

Yablonovitch:

No, not at all. And then, I was pursuing my own interest. I was doing something that was going to create energy for mankind, and it was going to be great. And then, I made a discovery, which was actually quite significant at the time, the mechanism by which laser light is absorbed in plasmas, which was a very interesting mechanism. It has to do with plasma waves breaking as if they were water waves were breaking on a beach. But the particular thing that happens when plasma waves break, because they're driven very hard by the laser, they emit very, very high-speed electrons. So, I detected the high-speed electrons that were emitted in the direction of laser polarization. They were a high enough speed that you could detect them as beta rays. And then, I made a little beta ray spectrometer and other things. It was a non-obvious mechanism for light being absorbed into plasma. It was interesting, I got some papers out of that. I got invited to various conferences and so forth.

Zierler:

I'll note parenthetically here, 1973, you have the Yom Kippur War, you have the Soviets and the Americans supplying the Egyptians and Israelis, and of course, you have the Saudis, in response to the American airlift, instituting an oil embargo against the United States.

Yablonovitch:

Yes, energy was a big deal. That influenced me. And even more so seven years later in 1979, when we had the second oil crisis. So that only reinforced my preexisting opinion, which was, "This is a very important research area."

Zierler:

But this was about geopolitics. Nobody was thinking about carbon emissions at this point.

Yablonovitch:

No, no, quite the contrary. In those days, an ice age was coming. They sat in line to get gasoline. But when that happened, I had already committed to that field, and it seemed like it was practical. And I taught Harvard's first two, and perhaps only, classes on plasma physics. I still meet people who took my course. But there was one little problem. As I got into it, about five years after, I realized it was bogus in the sense that, yes, it could possibly work, but the capital costs would be horrendous. And any rational person who knows anything about business understands that capital cost is usually the most important cost of almost anything.

Zierler:

This is not the only time that Edward Teller thought big things that turned out to be impractical with regard to lasers.

Yablonovitch:

Well, that's right, but I would say his compatriots, who promoted magnetic fusion, had the same problem, as they never took into account capital costs. They thought about scientific break-even. If you're getting more energy out than what you put in, you win. But there's a simple way I can explain why you don't win: If your output energy exceeds what you put in by a factor two, which seems very good, that means half the energy has to be recycled internally. Now, to recycle it internally, you need electrical machines and electrical equipment, accommodating an equal amount of power that you're sending out to the customers. The power plant needs to consume that power internally. So, you need the equivalent capital equipment of all your customers combined.

So, it made no sense from the capital cost viewpoint. And the people who came up with magnetic fusion, which preceded laser fusion, had no appreciation for capital cost. It was all about energy break-even, not financial break-even. So, I had enough common sense to say, "Well, wait a minute. The machine's going to be how big? The magnetic fusion reactor's going to be how big? Ten times bigger than a normal nuclear reactor?" Well, of course, even with normal nuclear reactors, the capital cost is everything. So, I realized the technology was bogus for that reason. And also, of course, they had not achieved scientific break-even either, still, to this day.

Zierler:

Were you thinking patents at this point? Were you putting feelers out to industry at all?

Yablonovitch:

No. I wasn't thinking patents, I was thinking more globally. I was thinking that things were for the benefit of mankind. So no, I wasn't thinking of patents. I was thinking, "Do we have a viable technology?" And I said, "No, all these people who go to these scientific conferences love each other, they think they're doing great stuff, and it's not going anywhere." Now, to reinforce my viewpoint I have to tell you one more thing. In 1979, the year I got out of that field, three editorials were published in Science Magazine. Not exactly editorials, they were published by a staff writer for Science Magazine, three successive articles, basically agreeing with me, saying, "The emperor has no clothes." And I said, "For sure, this is the end of it." Well, then, another article appears in Science Magazine. All the leaders of that field co-wrote a letter or article to Science Magazine replying, "No, no, no, we stand for the Science that we're doing. We're doing great stuff, and that staff writer doesn't understand, and so on, and so forth." And of course, to me, it was very unconvincing, but they won the day. And I hate to say things negative about other people's funding, but it continues to the present day, even though the promises of cheap electricity have not aged well, and nobody talks much about them anymore.

Zierler:

Who funded your research during your Harvard years? Did you have NSF grants, DoE? Well, it wouldn't be DoE, it would be AEC at that point.

Yablonovitch:

No, it was DoE already, and I think it was DoE for one project, NSF for another project. But I don't remember which project was which because at the same time, I was following another trend, and that was laser infrared dissociation of molecules. And it could be used for isotope separation. And everybody told me, "This is the most important thing, and you need to get tenure, so you have to do this. It's the most important thing you can do." And so, I did it, and we learned about the mechanism. It turns out that, effectively, all you're doing is heating up the molecule. Nothing interesting's happening. But it could become more interesting at higher power levels. Since then, people have pursued higher power levels, and it's still not that interesting. It's sort of faded away. Which is exactly what I expected it to do. And I look back with frustration. The only reason I did that is because other people told me I should do that because it's a hot field. And I didn't want to do that. I wanted to do things that made sense to me.

Zierler:

Did you have graduate students during the Harvard years?

Yablonovitch:

Yes, I had about half a dozen. And it was only a five-year period. But I think the graduate students did rather well. But that's because Harvard recruited very good graduate students to start with.

Zierler:

How did the slow realization on your part that the energy stuff would not pan out as you had hoped, change your overall research agenda during that time?

Yablonovitch:

Well, the year I was up for tenure, I had a sabbatical, and I decided to get into a new field because I really didn't think the other field was going anywhere. So, I took sabbatical with John Brauman in the Chemistry department at Stanford, and I tried to learn Chemistry. And I got a freshman Chemistry book. I'll tell you why: infrared multi-photon dissociation. I said, "I could do that with focused sunlight. I could dissociate molecules quite easily. I don't need a laser." And so, I learned the chemistry I had missed as a freshman. Then I realized that idea too, was impractical. But within solar, there was something that was practical, and that was solar electric panels. Now, the reason it was practical, it's just a passive thing that lays there, and it produces electricity. It was potentially economically practical because you were actually producing electricity. Joule for Joule, electricity is three times more valuable than heat, and the reason is, we consume heat to make electricity, but the efficiency is only ~33%, (though it's improving lately).

So that makes electricity three times more valuable. And then, there's another thing that happens, which is a regulatory thing. Because electricity production is controlled by regulatory agencies in each State, you're paying for electricity about ten times more than its energy value. To me, the solar panels actually made sense. So, I left Harvard, I went to Exxon. I had made the decision during my sabbatical, "Solar dissociation of molecules makes no sense, but solar production of electricity makes a lot of sense." And at Exxon, they owned the biggest solar cell company in the world. They had a group of RCA refugees who were staffing up their photovoltaic effort. I joined those people and started working on solar electricity.

Zierler:

I'm surprised with Exxon. I know that with soft matter, people like Dave Weitz and Harry Deckman-

Yablonovitch:

Exxon Research got into soft matter afterward. Before that, Exxon were the owners of the biggest solar cell company in the world, which meant that maybe Exxon produced ~10 megawatts of solar panels per year. Not very much by today's standards, currently ~100GW/year.

Zierler:

So, Exxon was in optical science because of energy issues, because they were interested in the sector?

Yablonovitch:

No, I think they had decided that they were going to be the Bell Labs of energy research, and they had a former Director from Bell Labs, Ed David. He was in charge. But you'll understand Exxon a little bit better if you understand what happened afterward. So, I joined them in 1979. I started working in solar, I published, actually some significant papers in solar. And then, what happened in the corporation is, there was a coup d'état. One day, the price of oil went down. And the company was shocked. And there was a revolution inside the company, and the winner of the revolution was a young guy named Lee Raymond. And he went on to be the chairman of Exxon. He was in his late thirties. He remained Chairman for almost twenty-five years. And the first thing he did, he says, "We're an oil company. This is crazy. Why are we doing solar?"

And here's what happened to me. I was hired by a Materials scientist, Fred Gamble, who was hired by Ed David, to make a Bell Labs of energy, who was hired by the president of Exxon Corporation, who believed in diversification. Then, in one year, which was early 1983 after the price of oil had gone back down, I discovered that my entire chain of command had been fired. Well, not exactly fired. The president of Exxon was asked by the chairman of Exxon to leave. And I naively said, "Well, according to the press release, he's leaving to spend more time with his family." And the people inside the company laughed at me and said, "That's never true. He was the president of Exxon, and as the president of Exxon, he was granted hundreds of thousands of shares every year," which is a huge amount of money. But he's leaving at age sixty-four, so he's missing one year of stock options. No matter what, he would've hung on for the last year. He got fired.

So, the president of Exxon got fired. Then, the guy who he hired, which was the president of the research company of Exxon, Ed David, got fired. And then, my direct supervisor got fired. And surely enough, within that twelve-month period, I was not fired, I was asked to stop working on solar. I was told I could keep my job. In fact, they wanted me to continue working, but I would work on things related to petroleum, which actually were quite interesting, petroleum extraction. And it's a whole education. In fact, I regard that as the best experience of my life, working at Exxon, because I was working side-by-side with Chemical Engineers. It was like getting a second PhD in Chemical Engineering and Materials Science. It was a fantastic experience. And then, I had yet a further great experience. I was rubbing elbows with all the RCA people, which was the competitor to Bell Labs. But they looked at the world completely differently. It was a whole different education being surrounded by RCA people versus being surrounded by Bell Labs people.

Zierler:

To go back to your point about Bell Labs being too basic, how did you feel about Exxon? Did they strike the right balance?

Yablonovitch:

Well, they struck the right balance for the company. Yes, they probably had no business putting that much effort into solar. And so, I couldn't argue with them from the business viewpoint. And by the way, Exxon was so big, just imagine some Latin American country, and there's a coup in the country, and there's a young new colonel who's taken over. And it was kind of like that. The Chairman fires the President of Exxon. But it was the right business decision, and you could tell it was because he survived for twenty-two years, dominating Exxon. It's slippery up there at the top sometimes. So, it was the right decision for Exxon, but I had to move on. And I actually went back to Bell Communications.

Zierler:

Did you already have a sense of what was impending at Bell with the breakup?

Yablonovitch:

No, quite the contrary. I thought I was going to the better half of Bell, which was Bell Communications Research, was still a public utility. We could continue research indefinitely. That turned out not be the case, as the telecommunications industry turned fiercely competitive.

But I learned something else during my period at Exxon. I did my PhD thesis on semiconductor optics. But when I was at Exxon, I learned about solar panels, and I learned about semiconductors where you have to attach a wire. Semiconductor Physics is completely different if you have to attach a wire to it than if you were just doing optical measurements. Because if all you do is the optics of semiconductors, you don't understand what semiconductors are all about. In fact, learning about solar, it all had to do with minority carriers, which is not covered well in Physics.

And the great aficionado of minority carriers was William Shockley. And he was such a hated figure that minority carriers disappeared almost instantly from Physics, even though it's extremely interesting. So, I learned a huge amount by getting deeper into semiconductors. When I went back to Bell, suddenly, I was qualified to contribute to things that really mattered to Bell, namely, optical communication. I finally had the training needed to be relevant for Bell Communications and Bell Labs. I understood semiconductors deeply. It turned out that the semiconductor laser and solar panel are brothers, they're actually the same device. In one case, you're putting in light and getting out electricity. In the other case, you're putting in electricity and getting out light. It's the same device.

Zierler:

Is this a eureka moment, or it develops over time?

Yablonovitch:

No, it was when I was trying to make the decision to go to Exxon and work on solar cells. I realized, "Well, it's not like I'm going off to some distant continent. It's the same thing, but they don't realize it." So, I felt, actually, pretty secure that what I was doing there would be quite relevant. In fact, even more relevant to Bell Labs than what I had done when I had previously worked at Bell Labs.

Zierler:

How else was your research changing at this point, just being in this new environment?

Yablonovitch:

Bell Communications was the smaller portion of Bell Labs, and so I got to meet the people who actually were doing communications stuff. I got to be friends with the people who grew the epitaxial layers. It was more compact, and therefore it was more vertically integrated. So that stood me in very good stead because one of the first things I did when I came back to Bell Communications and you have to understand my personal situation. I was living in New Jersey. I had worked at the Exxon research lab near where the refineries were. And then, Exxon built a glamorous new building about thirty miles west of Murray Hill, but I was living near Murray Hill this whole time. And then, when I went to Bell Communications, they didn't have a building yet, so we stayed in Murray Hill. By then, I was on my third successive job location, but I didn't move my house at all. I was just going to Bell Communications at Murray Hill. It was a great place. You had experts in every field. And then, I did something quite significant my first few months when I was back at Bell Communications. I had already developed a deep understanding of semiconductors through my work on solar cells, so I realized that it would be very good for semiconductor lasers to be strained.

Zierler:

What does that mean, strained?

Yablonovitch:

Well, it's just what it sounds like. You're pushing or pulling on it. Now, in practice, we don't push on it. What we do is, we grow an epitaxial layer, which is a layer that is lattice-matched to the substrate, but what if the substrate has the wrong spacing of the atoms? Then, the layer you grow on top of it could be squished. The atoms are crowding closer together. Or, it could be stretched because the substrate atoms are farther apart. So that's how we make strain. And I knew perfectly well this was a good way to make strain, and I also knew that the band structure was just right, and Bell Labs was a great place because one day, I was walking down this corridor, and I walked by Professor Lou Sham of University of California, San Diego, who was a consultant, and I said, "Am I doing this right with the valence band and this splitting of the degeneracy between the light holes and the heavy holes?" And he says, "Yes, yes. It's just as if you were off-center in k-space."

Then, everything became clear to me. He kept walking down the corridor. It was that brief a conversation. And in later years, I told Lou Sham, "Hey, without you, I could not have done it." And he says, "Well, okay, sure, whatever." And so, that was submitted for publication in the middle of 1985, and I proposed that semiconductor lasers should be strained. And the reason is, the breaking of spherical symmetry which lifts the degeneracy between the light holes and the heavy holes, and then the top of the valence band turns out to have a light mass. And if you have a light valence band, or if you had any kind of lighter mass, either in the valence band or the conduction band, it's much easier to make a laser. Way, way easier. And I went and explained this to our grower. And he said, "Are you crazy? I'm not going to strain my lasers. You're going to wreck them. This is not going to be reliable. It's a horrible thing to do." I said, "No, no, it's actually going to be more reliable because it's compressive strain. It's less likely to have any problems or get cracked." I submitted the paper for publication. But here's something I do sometimes. If I think an idea is really good, I will not submit it into a fast journal, I'll intentionally submit it to a slow journal because I want to get the priority date on the article, but I don't want to tell everyone right away. I want to have the opportunity, that for a few months, I can keep it to myself and figure out more of the repercussions.

Zierler:

And edit as you go.

Yablonovitch:

Not edit, but maybe submit a follow-up paper and so forth. So, as it turns out, there's a researcher, Professor Alf Adams of the Univ. of Surrey in the UK, who came up with the same idea, and submitted for publication a few months later. But he submitted it to a very fast journal, Electronics Letters. And so, his paper actually appeared before my paper. But I have the date of receipt several months before. And there was another problem. We used to have a lengthy publication approval process at Bell Labs. And it's very time-consuming. It could take two months to get it internally approved for publication. And then, I was kind of lazy and perhaps too sure of myself, and I left it in a drawer for another couple of months. So, I was very slow submitting the paper for publication.

It worked out. We share the credit with Alf Adams. It's great, he's very deserving. But neither Alf nor I could get anybody to grow this. They said, "No, that's going to be a crappy laser. I don't want to do it." But to his credit, he was more of an agitator than I was. He finally persuaded someone to grow this. And sure enough, just as we predicted, it was better, lased more easily, and was more reliable. And I was frustrated because years went by, and nobody was doing it, even though I knew it would be a great improvement in that field. And finally, it became adopted about seven years after it was published. And then, instantly, everybody made their lasers that way. There was a special issue of the IEEE Journal of Quantum Electronics, and the citations slowed down after that special issue, except that every semiconductor laser, except gallium nitride (which has a different crystal structure), that is used for telecommunication has strain, all the red lasers, the DVD players. But most importantly, all optical communication uses this.

And so, that was good. But it was something that I'd experienced repeatedly in my career, where I'd have an obvious idea, but nobody believes in it. And then, after a while, they finally catch on. So, I had a similar experience when I was at Exxon. I came up with the idea that if you can trap light in semiconductors–and make solar panels more efficient. Suppose you have a window, and the sunlight is shining on it. And then, I ask, "Well, how many suns of intensity are inside the window?" It's a plate glass window just like the ones in your office. The answer is, there's one sun. The sun is falling on the window, and you have one sun inside the glass. And then, I say, "Well, I do the same thing with a double-side-polished silicon wafer, and I put it out into the sun." And they said, "Well, how much sunlight do you have inside that wafer?" "Well, it's actually one sun, just like the window glass." Then, I say, "Well, let me get a silicon wafer." They have one side polished, but the other side is somewhat rough. And I say, "I'm going to put it out in the sun. And how many suns do you have inside?"

And the correct answer is fifty suns; Increased by 4(n squared), where n is refractive index. The index of silicon is very high, n=3.5. Squared is ~12. Multiplied by 4 is ~50. So just by breaking the plane-parallel symmetry of the solar cell, you can get 50 times more light trapped inside. It means, you could make the solar cell 50 times thinner and still absorb the light. So, I published it, and I even wrote a follow-up paper, and I wrote a paper on how this changes the theoretical efficiency of every solar panel. And we published on the limiting efficiency of silicon, much higher than expected. And as far as the solar industry was concerned, nothing. Nothing happened. And this is yet another occasion. Except, this time, I had to wait about fifteen years. Finally, about fifteen years later, at the industry trade show, there were companies selling the chemical reagents to roughen the silicon surface. The industry finally adopted it. It took fifteen years for them to understand. Few understood it. Many thought the reason I wanted to roughen the surface is to make a better anti-reflection coating. I said, "No, no, it has to do with statistical mechanics. You have to fill the internal phase space. The roughness doesn't even have to be very rough. It has to only make a fifteen-degree angle from normal. If you satisfy that requirement, the statistical mechanics of light changes drastically. You fill the internal phase space, and the solar cell becomes more efficient. And it has many benefits."

So, the benefit is that the expensive semiconductor could be much thinner, but also the voltage goes up by about a tenth of a volt, which in solar panels is quite a lot because the normal solar panel only operates at half a volt. So, if you add a tenth of a volt, it's kind of a big deal. So, the industry finally adopted it in the late 1990s. And I knew that it had finally been adopted because at the trade show, they were selling reagents and equipment for texturing silicon. And so, this is an experience I've had a couple times in my career. There's a terribly obvious idea, and the physics is so simple, or maybe simple to me, but people don't get it, so they don't adopt it. But, finally, they get it.

Zierler:

When does Sajeev John enter the scene for you?

Yablonovitch:

I wrote this into a Scientific American article, so you probably know about this incident. I had the idea of photonic crystals, and I can tell you how I had the idea. At that time, in the physics literature, people were publishing what's today called a vertical cavity laser but was then called a micro-cavity laser.

Zierler:

And at that time meaning what, mid-eighties?

Yablonovitch:

Yes, 1984- 1986. They were publishing vertical cavities. In other words, they were very short cavities. They were a half wavelength long, three half wavelengths long. Very, very short cavity. And they said, "Well, the laser physics is completely different because the cavity's so short." "Well, how was the laser physics different?" "Well, because the cavity's so short, you can suppress the spontaneous emission. You have mirrors, and the spontaneous emission cannot exit the mirror, and you will suppress the spontaneous emission." So, there were, a number of serious papers on the subject of micro-cavities in a twelve-month period in Phys. Rev. Letters. And I looked at it and said, "Hey, there's something wrong here. Because yes, you suppress spontaneous emission in the direction of the laser, but the spontaneous emission can still go sideways." So, what I did is, I said, "To prevent that from happening, just like you have periodicity on the vertical emission axis of the laser, you should also have periodicity in the lateral sideways directions."

So, what I did is, I just put parallel lines on a sheet of paper. Then I put parallel lines at right angles on the paper, and I had crossing lines. Those are my lateral periodicity. And then, at every cross-point, I imagined that you put extra material, so you kind of filled it in. You would have a diamond-shaped square just at the vertex where the lines would cross. And so, I filled in all the vertices, and I had a checkerboard. Those lines were actually the diagonal lines on a checkerboard, and where they crossed were the squares of the checkerboard. And I said, "Well, that's kind of interesting. That'll give you some lateral periodicity. And then, I said, "Okay, how am I going to combine this with a vertical periodicity? Because they all have to work together." So it dawned on me, "Well, to get the vertical periodicity, every place I have a black square, I have to put a white cube on top, and where there are white squares, I put a black cube." And you build that up in three dimensions. Then I have a three-dimensional periodicity. That's kind of interesting."

And then, I realized there's a problem. If it's cubic, you might have a forbidden gap that blocks the spontaneous emission, but at the corners of the cube, the wave vector would be √3 larger, the wavelength would be too short, and the cube corners wouldn't block the long wavelengths. But if the light went out toward the face of the cube, it would block the long wavelengths, but it wouldn't block the short wavelengths. And of course, since I was trained in Solid-State Physics, I knew about Brillouin Zones. And I said, "The forbidden gaps occur at the surfaces of Brillouin Zones. So, I need the Brillouin Zone to be as round as possible to cover all directions." I said, "Wait a minute. This three-dimensional checkerboard is not cubic. It's face-centered-cubic. The face-centered-cubic (fcc) Brillouin Zone is not quite perfectly round, but it's a lot rounder than an ordinary cube. Therefore, it has a chance to succeed. It's likely to actually block the spontaneous emission, no matter which outward direction was probed."

The way I thought of it originally, those authors are claiming to block the spontaneous emission. It's like putting Jell-O in your hand, and you're trying to squeeze the Jell-O. No matter how you squeeze, the Jell-O comes out between your fingers. And we had to find a way of squeezing it in all directions, so that it wouldn't squeeze out. And this whole analysis took about a two-week period. And then, I realized that by coincidence, the three-dimensional checkerboard had the roundest three-dimensional Brillouin Zone I could come up with. There are not that many interesting Brillouin Zones out there. A lot of weird ones, but a simple one like fcc, that was the roundest one. For example, if it was body-centered-cubic, the Brillouin Zone wouldn't be anywhere near that round. At that instant, when I connected the three-dimensional chessboard to the roundness of the Brillouin Zone, I realized I had something very major.

Zierler:

When you say you realized you had something very major, are you in application mode? Or are you in discovery mode?

Yablonovitch:

I was a little bit of both. To me, the way to solve applied problems is to convert them into fundamental problems. And then, you get a real solution. If you just look for a trick, you won't have a real solution. The things that are applied are fundamental in the following sense. If they're applied, everybody in the world does it, everybody in the world lives by it. And by then, it's been perfected to the Nth degree. And if something has been perfected to the Nth degree, and it's still not perfect, there must be a fundamental obstacle. So that's always been my belief and philosophy. If I approach practical problems in a fundamental way, I can make a fundamental discovery, which by the way, it will also be of practical use. So, I elevated that to a slogan. The statement is, "every technology that is not forbidden by physics is ultimately doable."

And I'm paraphrasing Feynman who said, "Everything in physics that is not forbidden is compulsory." Some people think: "In Applied Physics, you either have a trick, or you don't have a trick." No, Applied Physics should not be about tricks. If it's done correctly, Applied Physics is about something very fundamental. If you're going to make an improvement on something that has already been perfected, you need to come up with something new and fundamental. So, the applied motivation there was the lasers. Why are lasers always causing you trouble? Because you have to put so much current in them. And where does all that current go? It all goes into spontaneous emission.

So, by then, I was an expert on lasers because I already knew that they would improve with strain, which I had proposed perhaps twelve months earlier. So, with lasers, you're paying a heavy price in every laser to first pump it up with a lot of spontaneous emission, and finally, it lases. That's called the laser threshold. If you could get rid of the spontaneous emission, it would be fantastic for lasers. So that was the practical motivation. It was definitely influencing me. But the way I approached it is from a fundamental knowledge of lasers and what it fundamentally requires. So, I wrote the paper that way, also, as being fundamental. I did mention the laser application of photonic crystals, but I also mentioned the solar application. But what I mentioned in the solar application was, it doesn't seem to help solar cells. But in the meantime, since then, many people have published papers saying how great the photonic crystals would be for solar cells.

And when I re-read the original paper, it says it's specifically not for solar cells. It was originally meant for lasers with spontaneous emission problems. So that was my motivation. Then, what happened is that Professor Sajeev John of Princeton who sometimes who sometimes collaborated with Dr. Shahab Etemad of Bell Communications. Etemad said, "Here's a preprint from Sajeev John." I said, "Oh my God, I submitted that three months ago. How come PRL hasn't even given me an answer yet?" So, I called up the editor at PRL, and I said, "Look, you're refereeing this paper. And if you publish Sajeev's paper, you better publish my paper, too." So, he realized that it was the same idea.

Zierler:

And were you in contact with Sajeev at all at this point?

Yablonovitch:

No. Only afterward. So, what happened, then, we both got the papers published. Mine was published three weeks earlier, which I think the Editor did out of respect that I submitted earlier. But Sajeev deserves full credit. We share the credit. I thought, "Well, I think it's going to be a pretty important field." So, I drove out to Princeton to meet Sajeev, and I said, "Look, we're the pioneers of this field. And if we attach a name to it, that name will probably stick. So why don't you and I agree to call these Photonic Crystals?" And we did that over lunch, and we both agreed. And that's when the Photonic Crystal name was adopted.

Zierler:

Another nomenclature name, "Yablonovite". Who came up with that?

Yablonovitch:

That was Professor Tom Mossberg a physicist at the University of Oregon who was a friend of mine, and he just started calling it Yablonovite, and it caught on. But Yablonovite is just a particular design of photonic crystal. It's not the most common design, it just happened to be the first one which I made that succeeded. I have to tell you, part of the story was that the original design I had was incorrect. The reason is that, as an experimentalist, I checked various directions, but there was one direction in the crystal structure that I did not check, the K direction. It turned out that instead of having a band gap in the K direction, the original photonic crystal had a pseudo gap in the K direction. That meant the conduction valence bands were just touching. And that was a direction I had not checked experimentally. So, some theorists noticed this a couple years later, maybe a year later, and they published Phys. Rev. Letters; "Hey, that Yablonovitch guy was wrong." So, I had to modify the structure. But the modified structure is the one that's called Yablonovite.

Zierler:

Walk me through the process. Obviously, you know and Sajeev both know that you're really onto something big here. But how is it received more widely?

Yablonovitch:

Well, it's similar to the stories that were a little bit more applied. Like the strained lasers, or the light trapping inside the solar panels, it didn't catch on right away. We would tell people, and they would sort of scratch their heads and say, "How could that be? Only electrons have band structure." And so, I would say that it wasn't getting a lot of attention. In fact, I think in the first five years after the first paper was published, there weren't that many citations. And it was very frustrating to me. "Don't these people realize that this is really something?"

Zierler:

But were you conveying the discovery or the potential applications?

Yablonovitch:

The potential application was mentioned in passing in the original paper. And the reason it was mentioned in passing is that, "Well, it probably isn't practical for that application. There are too many interior surfaces, and you get surface recombination." So yeah, we were thinking about an application. The application did not work out to be practical. There are other ways of making the lasers better, like the strain. So, colleagues were objecting, they didn't think photons could have band structure. They had all kinds of crazy ideas. Or that if it was a good idea, it was already done by Brillouin eighty years ago. Which is sort of partly true. He did some interesting things back then. But then, after a while, we realized what we had done that was unique and unusual is that we had taken the idea of the band gap, which was actually first put forward Lord Rayleigh in a paper in 1887. But it was a one-dimensional band gap. That was 1887. Lord Rayleigh publishes the one-dimensional band gap.

Then, the real question is, why did it take one hundred years to get the two- and three-dimensional band gaps? And I have no idea why it took one hundred years. Maybe the laser application motivated me to delve deeper into it. The world wasn't ready for it. I have no idea why it took one hundred years to go to the two- and three-dimensional band gaps. But the one-dimensional band gap, Lord Rayleigh already pointed out, you need only minimal index contrast. The smallest index contrast already gives you a one-dimensional band gap. And then, it became a big thing in x-rays. In x-ray diffraction, they knew about this one-dimensional band gap, calling the effect Dynamical Diffraction. But these are very, very tiny band gaps because the refractive index in the x-ray region is very close to unity, like vacuum, so there's no index contrast to speak of.

There were two differences in our work. First, we went to two and three dimensions, and we pointed out that it wouldn't work at all in one dimension because in one dimension, you'd only block spontaneous emission in one direction. You needed to have it a fairly uniformly round Brillouin Zone in all directions. And so, there's a finite index-contrast threshold needed to get a band gap going in all three directions, and nobody knew what refractive index contrast that would require. And people are still arguing about that. But I think a diamond-structured photonic crystal from the group of Professor Kai Ming Ho of Iowa State Univ. succeeds in possessing a photonic bandgap employing an index contrast n=1.83, which is completely, of course, at odds with Lord Rayleigh, who said in one-dimension, any small index would be good enough."

At first there weren't that many papers on photonic crystals, but once we published the over-optimistic claim that we already had it in a face-centered-cubic photonic crystal,the theorists jumped on us because we had neglected the K point of the band structure. Then Prof. Kai Ming Ho proposed the diamond structure, a subset of face-centered-cubic which solved the problem. Because there was a little bit of controversy, the topic became highlighted in an editorial in Nature magazine. And then, people started arguing about it. And then, it started taking off. That took a good five years from our original proposal.

Zierler:

And is it really five years until the initial lukewarm at best feedback you were getting was starting to turn around?

Yablonovitch:

I would say that as soon as there was some controversy involved, people started delving into it.

Zierler:

As more people were getting involved, what did they add that did not occur to you and Sajeev initially?

Yablonovitch:

Well, the nice thing about the field, it's completely open-ended. You can use your imagination, come up with any crystal structure you can imagine, and have it perform any function that you want. And way more possibilities than what nature allows in real crystals. With photonic crystals, it's purely a product of one's imagination. You can do many different things with it.

Zierler:

During your time at Bell, when you were Director of Solid-State Physics, I'm curious because at this point, soft matter is coming online, condensed matter is being increasingly used. How anachronistic was it to be called solid state at Bell?

Yablonovitch:

Well, it was somewhat anachronistic, but it was appropriate because Bell Labs were interested in semiconductors. Semiconductors were the original poster child of Solid-State Physics. So, the name was perfectly fine.

Zierler:

What were the circumstances of leaving and going over to UCLA? You took your research agenda with you.

Yablonovitch:

Well, yes, pretty much. So, it was kind of similar to the situation at Exxon. They had lost interest, and they had in mind that I should do other things, and I didn't want to do the other things. So, the same thing happened at Bell Communications. Basically, it was owned by the Bell operating companies. There were seven of them, they could never agree on anything, but they started noticing every time we invented something, it would end up helping the cable TV companies. They realized that maybe they were not helping themselves with this research. And they pretty much decided to shut the research down. It was as blunt as that. And then, I was instructed, since I was a Department Head, whatever my title was, I had people working for me, I had to help them get jobs. And so, I helped all of them get jobs, they all got terrific jobs, many of them in Universities. Some of them went into software and became very wealthy. And then, I went to management and said, "I've done my duty, I've helped everyone get a job. Now, can you please fire me, so I can get the severance package, too?" And they said, "Oh, no. We're not going to fire you. We want you to stick with the company." So, they wouldn't fire me. And so, I never got the severance package. I had to just resign on my own.

Zierler:

To go back to when you were a graduate student, and you were really focused on applied research, at this point in your career, was working on a campus, being a Professor in the traditional sense more attractive?

Yablonovitch:

My initial stint at Bell Labs was only for two years, and then I went to Harvard as an assistant professor for five years.

Zierler:

No, but at five years, you jump right back into industrial research.

Yablonovitch:

So, I've worked at three large corporations, I've worked at three large universities, and looking back, I created four startups. The most fun was the startups. Being a cog in the gears of a very large organization is not that much fun. So yes, I was privileged because the situation in society and academia at that time was, you could go back and forth quite easily. And I think it's still true. Computer science is very hot. If you go and spend a few years at Microsoft or Google, and you want to go back and be a Professor again, you can do it. The situations in society and in academia have to make it possible, and it was possible for me at that time to go back and forth, which I did.

Zierler:

Were you putting out feelers to departments, or were you recruited directly by UCLA?

Yablonovitch:

Well, what happened is that I was told by Bell, "You have to fire everyone who works for you. And then, you have to help them get new jobs." And they weren't going to fire me because they didn't want to give me severance. All that did was just give me more time to find an academic position. So yeah, I started interviewing for academic positions.

Zierler:

What was attractive about UCLA at that point?

Yablonovitch:

Well, California's very attractive, as you've probably heard. And I had some other job offers. It's just the best offer I got at that moment in time.

Zierler:

Was the Northrop Grumman named chair part of the package?

Yablonovitch:

No, I didn't get that chair for about six years. I think most university professors will tell you that the chair funding ends up helping the Department, not so much the Professor.

Zierler:

It's different departments, it's different decades, it's different fields. How would you compare applied physics at Harvard to EE at UCLA?

Yablonovitch:

Well, obviously a huge difference. And I can express it in the following way. My Harvard friends are not going to like this. I was at Harvard as a student when the electronics revolution began. It began with the integrated circuit, and the microprocessor. The system at Harvard was that you took courses for two years, and then you find your research advisor and your field. And so, I finished the two years, and I had a classmate, and he asked me, "What are you going to do now that we're done with classwork?" I said, "I'm going into lasers. What are you going to do?" He said, "Well, I'm going into solid state." I replied, "Solid state? Don't we already have transistor radios?" And the year I said that, which was a pretty dumb thing to say, is the year the microprocessor was invented. And nobody on the East Coast understood that a revolution was going on. That included Harvard.

But not only did they not understand that a revolution was going on, it took about fifteen years for Harvard to realize that it was nowhere on the East Coast, it was happening on the West Coast, and Harvard was left out. The world was changing drastically, and Harvard was not part of it. They had no Professors who knew anything about it. It was very sad because I was a Professor during that period, and I didn't know about it. I didn't know the nuts and bolts of the revolution that was going on.

I have to share with you an experience I had my first month at UCLA. I was told that there was a younger colleague, Prof. Henry Samueli, who was doing great things in entrepreneurship. I was kind of interested in entrepreneurship. So, I had lunch with Henry. He was a circuit designer. First, he asked me something about optical communication. He said, "You just send pulses of light? You don't do any coding or use any of those coding schemes that we need for error correction? You don't do any of that?" I said, "No, we just send pulses of light." He shook his head and said, "That's crazy."

Then, he told me about his company. He said, "Well, we're going to do set top boxes for cable TV." It was 1993. "And we think this is going to be a very successful company. We think it might be worth fifty to sixty million someday." It was his second company, and this time they were doing it right, and were taking as little investment money as possible. He bootstrapped the company by doing design work for a fee that, which supported the company financially. Well, he also got very lucky because what happened in 1993? I think you were probably too young to remember, but a year later, the internet hit. And everybody downloaded a program called Mosaic, which was the first widely adopted browser.

And that was it. The internet started. So, a year after he started the company, turns out the chip he was designing was a digital chip for paid cable television. That chip, with very minor changes, could be adapted for providing digital internet and television. And the standards were already set for digital TV. Just repurpose it for the internet. So, he was about two years ahead of everybody in that field. And in that field, it's all about being ahead. It's not about patents. It's about having your product out ahead of the other designers. And by a stroke of luck he was two years ahead. His company was Broadcom which is a huge company today. He and his Co-Founder became very wealthy. His Co-Founder was actually his graduate student.

And the company, instead of being worth fifty to sixty million, at the peak of the internet bubble, it was worth fifty to sixty billion, and they each owned about twenty-five percent of it. So that was the difference. West Coast versus East Coast. In the West Coast, people had an idea that was practical, that you could make money on, and how to raise money. In the East Coast, you didn't have the ecosystem. And a very important part of the ecosystem, maybe the East Coast Professors were just as smart, but the East Coast Venture Capitalists were nowhere near as smart as the capitalists in California.

Zierler:

So, as you're saying, this entrepreneurial culture really didn't dawn on you until you got set up in LA.

Yablonovitch:

Yes, that was first moment I realized, "Oh my God, you can do really well, and it's relatively easy." And I just needed an idea. But at that time, I was really busy renewing my academic career, getting grants, and so forth, and I didn't have any great ideas. I just did what Professors are supposed to, get grants. But then, what happened, at the peak of the bubble, things were going totally crazy.

Zierler:

This is the tech bubble you're talking about, 1999-2000.

Yablonovitch:

Yeah. And I said, "Gee, I must have some good idea." At that time, also, everybody was adopting cell phones. The cellphone is kind of an amazing product. I heard one of the professors give a talk, and he said he had a better cellphone antenna. I said, "That's kind of interesting. Let me investigate that a little further." So, I investigated a little further, and it still didn't make any sense to me. So then, I went to another expert in that field. By the way, there are no such experts at Harvard or anywhere on the East Coast. But in the Midwest and the West Coast, there were some experts. And I said, "Can you explain to me how the cellphone antenna works?" And it didn't make any sense, since in those days, the cellphones were much smaller than the electromagnetic wavelength. I went to many experts who could not clarify these issues, and I said, "Well, there must be a business opportunity here. Because here's a very important piece of technology, the cellphone, and everybody's getting one. It's hugely important. You don't require a strong imagination." There were a lot of cellphones. You didn't even need to anticipate that the smartphone was coming to further boost its importance.

And yet, the people who were supposed to be experts could not explain the cellphone antennas to me. So, I thought maybe there was a business opportunity there, and that was my first company. And it was during the tech bubble, and you could just walk into any venture capitalist, and if you were a Professor, they trusted you with money. They thought you were a God who would make them wealthy. It was extremely easy to raise money. And a lot of people were making money on absolutely crazy ideas. So, I went to a few venture capital firms, but the one that I selected came from Silicon Valley. It was a short one-hour flight. There, on University Avenue in Palo Alto, there was a company, Sevin Rosen Funds Inc. And they sent Venture Partner John Oxaal to talk to me. He invited me back to explain it to all the other partners. It's great, better than sending a written proposal. You actually make the oral proposal right then and there.

It was a meeting of the partners, and they said, "Please wait outside." I waited outside for a while, and they came back and said, "Yes, we'd like to invest in your company. But you have a great reputation in photonics. Why don't you start a photonics company instead of a radio company?" And I said, "Are you guys crazy? There are hundreds of photonics companies. At best, only ten percent of them are going to survive. Do you want me to start a company with only a ten percent chance of survival? I refuse to do it." And so, they said, "Oh, in that case, we'll fund your cellphone antenna company." After we started the antenna company, and we quickly realized that what technology advantage we thought we had, we didn't actually have. In fact, I understood antennas no better than any of the other Professors I had met. So, we were in trouble, and it took us many years, actually, to find a way to make cellphone antennas better.

Zierler:

Where is UCLA in terms of IP and patents?

Yablonovitch:

They were troublesome. They were very troublesome. We had to come to a settlement with the University of California. They hassled us. And it was not a good experience. And I think they've reformed to some extent. Those problems don't exist at Berkeley. I think the whole system has reformed.

Zierler:

What kind of guardrails did you have to put up in terms of the graduate students that you worked with and the employees of the startups?

Yablonovitch:

Well, the students had to be completely at arms' length. You couldn't be half in the university, half in the startup. The company employees were not affiliated with the University. I had stopped working on things related to antennas in my University research. At the company I was only a Consultant and I kept that work completely separate from my University research.

Zierler:

Did your academic research suffer as a result? Or you were able pretty well to keep those worlds separate and be active in both?

Yablonovitch:

Yeah, I kept the worlds separate. And my philosophy was that I would come up with a business idea, which had to have good science in it. So, I believe this was another thing I wanted to mention, is that when people come up with a business idea, it's a little harder if we're scientists. Because not only does it have to be a good scientific idea, it has to be doable, it has to be financially practical, there has to be a market. These are all the normal things when you start a business. But if you're a scientist, it also has to have new science in it. That's an awful lot of constraints. Because it wouldn't interest us unless there was some new science in it. I That makes it extra difficult. And if money was my motivation, I realized I could've had money by providing something that society needed. But to combine that with fundamental science was very difficult.

So, I did manage to combine them. I came up with a good business idea that had good science in it. I sold the idea to the Venture Capitalists. And I hired the initial technical team. And then, I was out. I just came to the Board meetings. I said, "Look, within six months, the technical team knows more about the subject than I do." And I just continued with my day job. That was Ethertronics. Luxtera, the silicon photonics pioneer was about a year later. And I realized it's much more fun to do it with a colleague, so I co-Founded Luxtera with Professor Axel Scherer of Caltech, and he had some very good graduate students who were just ready to go and totally into it. And they had a piece of software that was useful. And so, we brain-stormed the designs for making silicon photonics practical. We weren't the first. We were probably the second. The difference is, we realized that was the exact moment to do silicon photonics. In Moore's Law, we had just arrived at the point where we were patterning structures on a wafer that were a quarter of a wavelength. At quarter of a wavelength, we could make photonic crystals and other photonic components. So that's what motivated us to start the company at exactly that time. Nonetheless, it still took a very long time for the product to sell in large volumes.

Zierler:

And what was the target for Luxtera? Who were you working for?

Yablonovitch:

The target for Luxtera was data communications. We had written off long distance communications because they already had good solutions, and there were many companies remaining from the internet bubble that were doing that. But silicon photonics was very well suited to data communications because it's like Wi-Fi. You need many more units. That would justify the design work on a chip. But we started shipping, in about 2008, but the chip volumes grew very slowly. And finally, the volumes in recent years have become very, very large because of the Data Center. The Data Center needed a huge amount of short distance internal communication. Silicon photonics is the best solution for that. So, a major Data Center will have thousands of our chips.

Zierler:

Why? What did you offer that they didn't have themselves?

Yablonovitch:

The data centers had short distance optical communication in multimode fibers, not single mode fibers. So, the data rate was limited, and the distance was limited. With a multimode fiber, you can maybe go a couple of hundred meters. Sounds like a lot, but if you go up to the Pacific Northwest and look at the data centers, they're a kilometer long. And so, our solution was single mode optical fibers attached to a silicon chip. It was very inexpensive, and yet, it had the highest performance. When the data centers came along, that made the company. For a chip to be interesting, we need to sell about a million. The reason is, anything you develop that's sort of like a chip or a laser, the cost of designing it is about $10 million. That's before you pay for the chip. So, if you sell ten million of them, you're going to have to charge one dollar each. And if you sell one hundred million of them, like a DVD laser, those sell for about $0.10 each. And so, there's this hierarchy. Unless you have a very large number of units, you can't justify designing a chip. And the data centers meant the number of units had now grown large enough to justify mass production.

Zierler:

How'd you do with the dot com bust?

Yablonovitch:

Well, the company started a year after the bubble. And we had very good venture capitalist backers. They saw we were doing something that was inherently new and valuable, and it wasn't going away. So, they carried us right through the bust. So that's the main thing. With venture capitalists, it's very important to get the best, the ones who have scientific understanding and enough conviction to carry you through the bad periods.

Zierler:

Of course, you remained interested in energy efficiency issues throughout this time. I assume that's where Alta Devices comes from.

Yablonovitch:

Well, you have to remember that my interest in solar ended very abruptly when Exxon lost their interest. And I felt very cheated. We had some good ideas, and we couldn't develop them. So, I kept thinking about it in the background. When I was at Bell Communications, one of the background inventions that we had was epitaxial liftoff. So that was one of the good things about switching from solar cells to Bell Labs. Solar cells are often just about silicon. Silicon is an old material. At that time, there emerged III-V semiconductor alloys, of great importance for optical communication. By the way, optical communication and the strained semiconductor lasers are exactly what enables this telephone conversation. Otherwise we wouldn't be able to see each other on Zoom. When I started at Bell Labs the first time, in the display area in the lobby was a Picturephone. And the Picturephone was rather pathetic, and there was no market for it. And they had to shut that effort down. The market is there if you don't charge people very much. And so, now, we're having this discussion at almost no cost, as Zoom subscribers.

Zierler:

To what extent were you ahead of your time when, at Exxon, you had these ideas about solar, but you didn't get the political or resource support that you otherwise needed? In other words, when you get back involved in 2006, 2008, had the technology really come that far? Or did you have the same ideas that you could apply now in a more positive space?

Yablonovitch:

What happened is that after the mid-1980's there followed a very bad time for solar. The markets dried up, there wasn't any money to be made. It was just a very tough period for solar. And that period lasted until about 2005. In the meantime, I had it in the back of my head, "Here's the right way to do it. Someday, it'll be the right time again."

Zierler:

Also, 2005, Hurricane Katrina, An Inconvenient Truth. Global warming is very much on the radar at this point.

Yablonovitch:

Yes. And it influenced politics in Germany. So, I've asked experts in the field, because the upsurge occurred in 2005, "What happened in 2005 or around that time? The early 2000s." Germany needed to make a coalition government, and the Green Party would make a coalition with the Christian Democrats provided subsidies would be given to solar panels. And those subsidies changed the world of solar completely. And everybody who was in the solar field at that time experienced this. They don't call them subsidies, they call them Feed-In Tariffs. But they basically guarantee very high prices for the solar electricity. The utility was obligated to buy the electricity at very high prices. "No matter what it costs, the utility will buy it. They had to install many panels, regardless what the cost." And that was a tremendous boon the industry, and many German solar panel companies started at that time.

But it did not have a happy ending. At least for those companies. What happened is that China wants to be the manufacturer of everything important. And you could understand it. The big problem in China is that they need jobs. They have too many farmers, and they need to get them off the farm and give them jobs. There are just way too many farmers. And so, they need jobs programs. Well, many countries have jobs programs. But China has more jobs programs than any other country, and solar became a jobs program in China. And you can't compete. Once it becomes a jobs program, it doesn't matter how good your technology is, doesn't matter how low your costs are, and so forth. So, what happened in China is that the factories were given free land for the factory. The Chinese Provinces would build the building for them and provide the factory a zero-interest loan for the equipment, and would subsidize the labor because otherwise, those workers would be on welfare. Those were the unemployed farmers.

So how many expenses does such a company have? The land is free, the building is free, the equipment in the plant, well, zero interest means it's free. You have to pay it back in principle, but that means you're paying nothing. And the labor is the only part that's left, and it's subsidized. So, as a result, the Chinese factories have brought the price way down. They are at each other's throats, but they've put all the other solar companies in the entire world out of business. China dominates the manufacturing, but they're making little or no money from it. They're subsidizing it. But it's terrific if you want to see a lot of solar panels in the world. So, I'm looking out at the apartment building out the window, and you have two giant panels on their flat roof. And each one is about ten meters by ten meters. So, it's a totally amazing and unbelievable revolution, compared to the early days. I said that we are using the strained lasers as part of the communication we're having. But we're also using electricity. And this is true for almost any State, but especially in California, that part of the electricity is coming from solar panels. And every solar panel has the "Yablonovitch Limit", the light trapping concept that I am proud of.

Zierler:

I assume this applies to Tesla's roof panels as well.

Yablonovitch:

Oh, yes, absolutely. That's the way silicon solar panels are made by China, by every country. Starting in the late nineties, they put the light trapping in it. And the light trapping is subject to the Yablonovitch Limit. I suppose I should be very happy about that because that means that there are at least a couple of my innovation that are actually used. That was my original goal. I wanted to invent things that people would actually use and would make their lives better. And so, I have a few of those things.

Zierler:

Why the move up to Berkeley? Were you looking for something new?

Yablonovitch:

Yes, I was looking for something new. But now that I've been here for a while, I realize that they're both great universities, they both do well, they both have great students.

Zierler:

Was one of the things that was attractive the joint appointment with the lab and the department?

Yablonovitch:

Yes, it looked very good, but in practice, in the joint appointments, you're still on your own. You have to raise money from the Department of Energy. So, it doesn't give you that much of an inside track.

Zierler:

I did not know that Kavli funded nanosciences as well. I thought they were only doing theoretical physics.

Yablonovitch:

No, they're doing some basic things like astrophysics and theoretical physics, but they're also doing some applied things like nanotechnology.

Zierler:

Were they a funding source for you specifically?

Yablonovitch:

No, it was sort of more of a group infrastructure thing. And I think I funded a postdoc once.

Zierler:

And in the department, tell me about James and Katherine Lau.

Yablonovitch:

Well, James is a graduate of the department, and he was one of the pioneers in data centers. He made one of the first data center companies. And there was a time about ten years ago, the University had a program to raise philanthropic funds, and James was kind and loyal enough to Berkeley to give back.

Zierler:

Did you continue as intensively in startups when you got to Berkeley?

Yablonovitch:

It was about the same. It was never that intense. I kept my day job, and I told you my secret. I don't do much. Once the employees know more about the Science and Technology than I do, which takes about six months, I'm just there as a consultant Advisor, and I'm on standby. I get to work full-time on my day job, University Professor. That enables me to start more companies. There was the same deal with the second company. Then I started a third company. Then I started a fourth company.

Zierler:

So, what did you get involved with, in startups when you got to Berkeley?

Yablonovitch:

That's when I started Alta Devices. There was kind of a gap. I started Ethertronics for the radio antennas. But I should mention that the principle we discovered at Ethertronics ended up in everybody's cell phone. In particular, it's very noticeable on the iPhone six because it has an external antenna. I'm going to write a paper on it someday, how the iPhone six works. Apple probably came up with the idea themselves, refusing help from my company, Ethertronics. They have some smart people at Apple. And then, the second company was Luxtera, which was the pioneer in silicon photonics. Each one of these was trying to prove a scientific principle. The principle in Ethertronics was, how does Maxwell's equations really function for cellphones? And it turned out that no, it had not been properly applied to cellphones. With Luxtera, we answered whether we can actually do optical communications with crystalline silicon processed in a normal electronics fab? And the answer was yes.

The third company, Luminescent Inc. was jointly with my colleague Stan Osher, a brilliant applied mathematician. And he had taught me some math, and I said, "This is fantastic. Every scientist needs to know about this math." We started the company, and the company did okay. Every chip in the world uses that math now. I was a go-between from Stan Osher's mathematics to knowing what the technological application should be. Intel never became a customer. They saw how it performed, they kept silent, and they developed it internally themselves but wouldn't tell us. So, every Intel microprocessor has that mathematics in it.

Zierler:

On the academic side, what were you doing at Berkeley?

Yablonovitch:

There was lots to do. While I started those three companies, I was very heavily involved with quantum computing. It was definitely a full-time job. And as I said, the companies didn't interfere with my day job. And so, I was able to start the multiple companies. After the math company, Luminescent, I took a break of a few years, and I went to Berkeley. Then, it was also around that time we realized, "Maybe this is the right time for solar." Because the German subsidies had kicked in. Suddenly, every solar company was very valuable. So, Prof. Harry Atwater of Caltech and I started a solar company, Alta Devices Inc.

Zierler:

Who were some of the key people that you worked with in quantum computing?

Yablonovitch:

Well, I worked closely with my algorithm colleague Prof. Vwani Rochowdhury. And I worked with Prof. Hongwen Jiang who is a low temperature expert, because we were doing semiconductor spins as the qubit. Today, it looks like there might be better qubits, but spins in semiconductors are still flourishing. We told people to stop doing it in the III-V semiconductors because three and five were both odd numbers, they had odd numbers of protons in them, and therefore, they had nuclear spins that would disturb the qubits. That's another example where it took the field at least fifteen years to realize that you weren't going to do this with III-V semiconductors. I kind of fell on my sword saying, "If you don't fund this silicon-germanium work, I'm going to get out of quantum information processing." So, I got out of it. But now, the silicon-germanium work is back, as it finally dawned that the III-V's were hopeless. And actually, Si-Ge is doing quite well now for qubits.

Zierler:

Just to bring the narrative up to the present, what have you been working on in the past five years or so? What's been most compelling to you?

Yablonovitch:

Well, I can tell you, there are two things that have preoccupied me that are, I think, very physics oriented. And one of them is a recognition that goes back almost twenty years, to find out, what is the scientific problem with chips? And the scientific problem is that they operate at one volt or thereabouts. And the noise level is less than one millivolt. So, they're operating at 1,000 times more voltage than they need to operate at. Which means they're consuming a million times more power than they should consume. And so, that's low hanging fruit, as we say. It's something that's begging to be solved. So, I was awarded an NSF Center, and I've been leading a multi-University team to do that. We've done many good things, but we haven't quite solved that problem. Instead, we've defined the reason why the problem is so difficult and a planned a path forward. But the path forward is going to be very difficult.

We defined a slogan called "the millivolt switch," which meant that if only you could have an electrical switch, (a transistor) that you could turn on and off with only a millivolt, then you'd solve the problem. In transistors, the reason why they take a volt is that they're not very sensitive. It takes almost an entire volt to turn to a transistor on and off. Well, maybe eight-tenths or six-tenths of a volt. But that's the reason why electronics is inefficient. And so, I think that one is still a great opportunity for the future. But it's rather difficult to retain the same Si materials and solve that problem. Because one of the things about the normal von Neumann architecture computers is, you have switches, and they have to be either off or on. And to have it either fully off or fully on, that takes a fair amount of control voltage. And that's where we're stuck. So, in the E3S Center, we redefined it as a materials science problem, but a difficult one.

But I think it might be possible to achieve it using, not carbon nanotubes, but graphene nanoribbons. But these nanoribbons are not really graphene the way it's usually understood. These are just another version of polymer electronics. But now, there's a rationale for using polymers as transistors. The rationale is that, if you do everything right, potentially, they would be more sensitive.

The other thing I'm working on now, which has me very excited, is a very surprising thing to me. Because I was brought up on circuits. If you recall, my high school science fair project required me to make an instrument that would measure the IV curve of solutions. I know circuits backward and forward, I'm very qualified to teach circuits in my department, yet circuits have a property that surprises me. It's kind of shocking. And you'd think at this stage of my career, I would know everything about circuits, but here's something I didn't know. When you can apply a voltage or a current, the other currents will adjust themselves to dissipate the least amount of power in the circuit. I always knew that. It's called the Principle of Minimum Entropy Generation. In fact, that is in the Feynman lectures. And it's a Principle that's in somewhat disrepute. But Feynman liked the Principle. He has half a page on it in the Feynman lectures. In contrast, the Feynman lectures, have many pages about the Principle of Least Action. So, throughout physics, there are many principles, "Least this," "Most that," etc. And these are part of physics. What we've realized, just in the past twelve months or two years is, that physics does maximization and minimization, it does optimization. But optimization is also the center of Machine Intelligence, it's the center of many things in computer science. And physics does it for you and has always been doing it for you. And we realized that. Alternately we could go for the Principle of Least Action, but that's hard to use. Instead we use the Principle of Minimum Entropy Generation. Now, entropy generation is just heat, the amount of heat you produce. It's a rate, and the physical system seeks out the state of minimum rate of entropy generation.

That Principle was first put forward by Onsager in 1930. Onsager is a Nobel laureate, and a great theorist. He's the one who figured out that in many dissipative processes, the tensors are symmetrical. And so, for example, heat flow driving electric current and electric current driving heat flow, share the same coefficient. In the course of analyzing the responses of a driven physical system, he came up with this Principle of Minimum Entropy Generation. The Principle has been controversial since then because there are exceptions. It's not as solid as some other physics laws. I think it's actually perfectly reliable under the proper conditions. In every circuit that you make, the current readjusts to minimize the heat generation. And in fact, you could use that Principle to derive the normal circuit laws. Equally well, you can derive that Principle from the circuit laws. But once you recast circuits as a minimization principle, you say, "Wait a minute. I can do computational optimization with ordinary circuits." And so, I think that's going to be very huge. I think it's going to be one of the major forms of computing, which we like to call Onsager Computing. It's not going to replace von Neumann computing, but it will operate alongside von Neumann computing. It's going to be in machine intelligence accelerators, but there are many other types of optimization problems for which this might be applied. So, there's just been a little, tiny bit of work so far, about half a dozen papers on this subject, not only from ourselves, but also from other groups. I think it's very exciting.

Zierler:

A very present question, just to bring our discussion right up to the present day, one of the great narrative lines that corresponds with the chronology of your career has been, first, the boom in manufacturing in Asia, and now, right up to today in 2021, especially in China, the promotion and support of basic science in China. This is as much a sociological or political question as it is a scientific question, but from your vantage point, sort of coming of age at Bell Labs at the height of American power in these things, where do you see the United States as a global competitor looking forward into the twenty-first century, given what's happening in Asia right now?

Yablonovitch:

China is a very important country going back into ancient times. I don't have to tell you, many of the important inventions came from China. And that would include, for example, gunpowder, for better or worse, and paper. Paper was invented in China. It's kind of shocking. The Romans did not have paper. Paper was invented in China, a few hundred years after the fall of the Roman Empire. So historically, I think China has been very successful in science. And you're right, it's a political decision because they needed to strengthen their education system. They are finally strengthening their educational system. So, they're going to be a very strong competitor in education. And I know there's a bit of a disagreement between me and some of the members of my department. I believe that there will come a day when the Chinese graduate students will stop coming to the United States because their own universities will be just as good.

Zierler:

Not because of the Trump Administration, but because they don't want to come.

Yablonovitch:

Graduate education in the USA won't be necessary, since their universities will be just as good. They're not there yet. Maybe it's taken a little bit longer than I expected and they expected. I believe that they're being held back by their political system, which has both its good and bad points. Obviously, they are in a situation now where there's enough commerce and business coming in to pay for all these professors doing good work. So, they're finally promoting their university sector. But I would say they're so far behind in the university sector, it will take a very long time. Just like starting a new university in the United States. It'll take one hundred years to get a reputation. And I think that's going to happen in China. So, the time scale's probably longer than I thought. But there are other problems in China. You need a steady political system for one hundred years. I don't think the system is stable enough in China that you could guarantee one hundred years from now, they're still going to be supporting education. So, I think the potential is huge, and if they can maintain a political stability for a long period of time, they're going to be leading competitors in world science. Just like they were 1,000 years ago. But the same applies to the United States. Who says our political system is going to be so stable?

Zierler:

That's a very open question circa 2021, isn't it?

Yablonovitch:

Yes, that's right. And so, it's rather difficult to predict the future. What we do have going for us is, we've established great universities, very competitive. But you notice that the Europeans were coming to America for their education after World War II, and then they stopped coming because they have great universities, too. And their universities are much older than our universities. But the European students stopped coming. There are few exceptions. The adventurers still come here. The time will come when the Chinese universities will keep their own best students, and the students will have no desire or motivation to come to America for graduate education. That will come to pass, but who knows how long it will take, and who knows if there's going to be enough political stability to make that possible?

Zierler:

For the last part of our talk, I'd like to ask a few broadly retrospective questions about your career, and then we'll look to the future at the end. So, first, I certainly would not presume to bother you in explaining all of the awards and honors that you have been recognized for over the course of your career. But I wonder if any step out as being most personally meaningful to you.

Yablonovitch:

Well, I do some research, it doesn't get noticed for a while, and eventually it becomes adopted. So as long as it eventually gets recognized, I'm really happy about it. I think just about every significant thing I've done in the past has been recognized. So, I really have nothing to complain about. For example, I received the Cherry Photovoltaic Award recently. The strained semiconductor lasers, I got the Rank Prize for that. Basically, I've been totally recognized, and I really have nothing to complain about. I've fulfilled my ambition. There are things that I invented that are used by everybody, every day. Usually, of course, without users being aware of it. And so, if you're just looking at a cellphone, you're actually looking at antenna functionality that was first developed by Ethertronics, which was later adopted by other companies. We already talked about the strained laser being part of what makes this internet conversation possible, internet communication. You can blame me for the efficiency with which email fills your Inbox.

Zierler:

Looking at your career trajectory in sum, it's fascinating how you've toggled back and forth between academia, industrial research, and startups. What have been some of the primary advantages and disadvantages of not just staying at one institution your whole career?

Yablonovitch:

Well, I can tell you one giant advantage is that I'm very lucky to have lived to my age. I've outlived many institutions. So many companies that were terrific stopped being terrific, like Bell Labs. And this is true about most businesses. It's very difficult to have a business that survives well, over a long time period, because business is constantly changing. With universities, the business is to educate the young, so it doesn't change that much. And then, teaching is fine, but the research support does fluctuate. So, in the universities, a lot of research funding is somewhat conditional. Moreover, you have to adapt. My biggest frustration is that some official in Washington tells you what the important problem is. And I've been rebelling against that my entire career. I want to identify the important problem. I don't want to be told what to work on. That's been an issue. It's true at universities and true at most companies. Those are the frustrations.

Zierler:

As somebody who's outlived many of these companies, you're in a position of seniority right now. I'd like to ask broadly in your career as a mentor, either to undergraduates, graduates, postdocs, young people that work in the companies that you've helped found, what have been some of the character traits, intellectual traits, ethical traits, no matter the decade that you're talking about, no matter the company or scientific enterprise, that you've seen in younger scientists where you know somebody is on the road to success?

Yablonovitch:

Well, success is many different things. It doesn't have to be scientific success. Just for success in life, you have to be of good character. Your word has to be trustworthy. If you promise something, you have to deliver it. Then, when you get to science, you have to have the talent. There's no substitute for talent. My only comment about talent is that my students, who were great, were great before I got them, were still great afterwards. And I don't think I necessarily added that much.

Zierler:

Well, you'll get some pushback on that, I'm sure.

Yablonovitch:

No, they were and are fabulous. And I question whether I added very much to how wonderful they were.

Zierler:

As you say, there might be some delay in all the things that you've worked on, but eventually they get adopted and recognized to one level or another. Is there anything you've worked on that has proved to be thorny where you kept on hitting a wall and never found a way out of it?

Yablonovitch:

Well, solar, for example. Atwater & I had to shut down the solar company, Alta Devices, two years ago. We hold a world record for solar cell efficiency. We have a process that potentially could make solar panels as cheap as paper. Yet, the subsidies in China meant that nobody would invest in it. And I can't criticize the financiers. I can't offer them anything at this moment in time because with the Chinese subsidies, it doesn't make any sense to have a better solar technology. They're selling the panels at such a low cost that there's no point investing in that field. And financiers know it, and they won't invest in that field. So that is very frustrating to me. It's a great opportunity, holds a world record, has held it since 2011, will continue to hold the world record for a very long time. In fact, for many years, the only people who beat our record was us.

So that's very frustrating to me. But some things just take time. And if you're talking about an energy transition, those usually take about one hundred years. I think we're in the middle of an energy transition, where after the transition, we will be one hundred percent solar in primary energy. But we have to invent a lot of things before that happens.

Another regret I have is that if you look at it, early on, I became interested in things like energy. I was listening to Edward Teller and so forth. But I looked back, and I said, "No, no, I should've recognized the importance of information technology and dived into it earlier." As it is, it was my second Bell stint in Bell Communications, where I finally took up the opportunity to be relevant toward telecommunications, which is the physical foundation for information science. And so, I wish I had immersed myself into that much earlier. And as is, what I'm doing now with using physics of optimization, that could have been done much earlier, too. So, I do have some regrets in that regard.

Zierler:

To bring it all the way back to that formative moment where you cracked open the Feynman book for the first time as an undergraduate, what in physics, as the foundational science, if you will, has stayed with you that informs the way you see the world, the way that you interface with technology, the way that you're inspired in innovation, that is close to you throughout your career, no matter what you've been working on?

Yablonovitch:

I just read a Feynman biography, and I learned that he just wanted to explain all of physics in his own simple way. And he put that into the Feynman Lectures. And that's what I want. I want to be able to derive things in the simplest possible fashion, so everything becomes understandable. But given that the Feynman Lectures have already been written, I'm hoping to contribute more to an Applied Physics version of the Feynman Lectures. Why do computers act the way they do? Why do we do computations in a certain way? How does a solar cell work? What determines the voltage of a solar cell? I'm writing a paper right now on the voltage of solar cells. You'd think that would be completely worked out. I actually wrote on this many years ago. There are still some nuances left to work out. But even after you work them out, people don't necessarily understand. What's the simplest way of explaining it?

So, for example, with solar cells, I put together one of my slogans, "A great solar cell has to be a great LED." And it's really hard to explain to people why it's good for a solar cell to emit light, to give back some of the light. It's very, very hard to explain that to people. I'm trying to come up with a simple explanation. So that's what I'd like, simple explanations for everything. And I'm inspired in that by the Feynman Lectures. He had a simple explanation for everything.

Then, there are other questions in business. You don't necessarily want to do what everyone else is doing. You could probably execute well, but you don't want to do that. There has to be a scientific basis for what you're doing in business. Every professor I know who's in business has a scientific plan behind it. They're trying to prove something scientific. Very few of them are doing it just for the money.

Zierler:

Last question, looking to the future, a narrative thread that connects everything that you've done in your career is real life practical application, fundamental discovery, and a pretty good nose for where there's business opportunity. So, using all of that perspective and wisdom you've gained over the course of your career, looking forward, what are the kinds of things that you know you want to be working on for as long as you want to be active?

Yablonovitch:

Well, I mentioned a couple of them as sort of current research already. Mostly, I would say, it's very difficult to predict the great things of the future. Early on, I realized that because I know science, I should be able to do a better job of predicting the future than other people. And yet, I look back, and I did a terrible job. You remember when I said, "Transistor radios? Don't we already have those?" And I completely missed the microprocessor revolution. So, I would say that I don't have that good a record of predicting the future. Bill Gates has a good record. But even with Bill, it's in a very narrow area. I wouldn't count on him to predict outside his own area. Although, he's dedicating a lot of his own attention to medical research now. So, I would say it's really hard to predict the future, and if you have a talent for that, even in a narrow area, follow it. Because if you predict the future, you will own the future. And that applies, also, to science. What's going to be important in science in the future? And the great scientists, how did they become great? They put themselves in the right place at the right time to address a problem. Well, yeah, it was coincidence, but they also prepared themselves well.

Zierler:

It has been a tremendous honor and tremendous amount of fun to spend all this time with you. I'm so glad we were able to do this. You've been so generous with your time and your insights. I really want to thank you so much.

Yablonovitch:

I appreciate it very much.