Oral History Transcript — Dr. Marlan Scully
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Marlan Scully; July 15 and 16, 2004
ABSTRACT: Scully’s passage from petroleum engineering in Wyoming to a theoretical physics thesis at Yale University under Willis E. Lamb, Jr. His teaching physics at Yale and MIT in the late 1960s and early 1970s. His controversy with Edwin T. Jaynes on semi-classical vs. quantum electrodynamics. Professor at the Optical Sciences Center at the University of Arizona in the 1970s. His working with Kirtland Air Force Base, Redstone Arsenal and Los Alamos on defense-related projects, including laser anti-missile missiles. His position at the Max-Planck Institute in Garching, Germany. His collaborations with Julian Schwinger and others. The Origins of Scully’s “quantum eraser” idea and its application to new devices. Mode of working with graduate students.
Bromberg:You grew up in Wyoming. How did you get into physics?
Scully:I was fascinated by physics. When I was in the third grade I saw an article in a magazine by Edward Teller, in which he said in effect, “The great thing about science is that when anyone profits, everyone profits, whereas if you are a salesman, if one man sells a car, that means that other salesmen have lost the opportunity to sell to that buyer. But in science, it’s not like that.” I thought that was very interesting, and I went on to look in microscopes and follow up on this strange breed of man. It was a wonderful time growing up and being educated in Wyoming, where there was a lot of oil money and a lot of excellent educational opportunities — good teachers and facilities.
Bromberg:Were you from a family with any scientists?
Scully:No. They weren’t scientists as such, but they were all autodidactic engineers: Diesel mechanics, oil field drillers, and homesteaders — self-sufficient people. In that sense, they were engineers of their time.
The business of interesting young people in science is something that I am involved in. Scientists and engineers are generating something useful. Tomorrow there is a young lady coming and I would like her to meet you. She is a high school student, and I would like her to see what you do, to learn of the many interesting ways there are to do science, and to enjoy science.
Bromberg:Have you been working in K-12?
Scully:Yes, I’ve frequently lectured and taken demo’s to grade schools; trying to help young people develop their interests. I run a school for undergraduates each summer in Wyoming. I bring in first-rate scientists, including Nobel Prize winners. So at the level of undergraduate science I’ve been involved for a long time. And also I try to work with individual young people and organize visits to the university whenever I can.
Bromberg:So then is it right to say that you will have been interested in applications from the very beginning? That is, in engineering applications from the very beginning, because of this ambiance of your family and your environment?
Scully:Exactly. In fact, I started at the University [of Wyoming] thinking I would become a petroleum engineer. And as I got into it I discovered that physics was very interesting, so I ended up getting a degree in engineering physics. As a senior, I was called to the Renssalaer Polytech to take graduate courses. After graduated, I went to work for General Electric in Schenectady. They paid me to study nuclear engineering at Renssalaer.
Bromberg:And General Electric financed this?
Scully: Yes, in the good old days when we called it “Generous Electric”. I asked the Vice President Guy Suits, “Why do you guys do this? What do you get out of it? Paying me to go to school.” And he said, “Well, you know, we are taking from the body of knowledge and we feel we should add back to it in equal measure.” What a wonderful, high-minded attitude!
Bromberg:In the sixties, GE could afford that attitude.
Scully:O.K. That was the golden era. And the country profited from it. Look at all the wonderful science and technology we have because of that. So I studied for a year at RPI and got more immersed in quantum mechanics. Then one of my professors said to me, “You know Willis Lamb is coming back to the States from Oxford. He’s going to Yale. Why don’t you go to Yale and work with Lamb.” That’s how I got deflected from an engineering career into physics — always thinking about experimental physics. You know, Lamb got the Nobel Prize for doing experiments. He experimentally measured the Lamb shift. And I thought, “What a great opportunity to learn theoretical physics and to interface with experiments.”
And that’s what I’ve always done. I’ve always had experiments going on, and doing things that were perhaps a bit unusual. You know, we make lasers now without population inversion; we can detect anthrax with lasers, and invent the quantum eraser.
Bromberg: So it wasn’t particularly the laser that excited you. It was Lamb that excited you.
Scully:Yes! The early days of the laser, we didn’t understand how some of these wonderful things could happen. For example, there’s a story about Charles Townes and Niels Bohr concerning the line-width of the laser, and why it is so narrow. Bohr didn’t believe it. Other people were trying to understand how it is, from a photon point of view, that you get coherent radiation. You go from a photon picture, which is the antithesis of coherence, to a coherent beam of light. A deep philosophical question, that Roy Glauber helped us to understand. He pointed out that it was a difficult problem that we wouldn’t answer until we got a more careful theoretical analysis of the quantum nonlinearities of the laser.
So Lamb gave me this problem to develop the quantum theory of the laser, and went away for a summer at Les Houches. He came back, and I had been going down one particular path, which he sort of nudged me away from. He let me go again, and within a few months, we had it. It was the interface between physics and device; it is the fundamental physics of that device that characterizes the interface between basic physics and engineering science.
Bromberg:So that thesis starts from the question of why you get coherence out of photons?
Scully:Yes. If I can paraphrase Roy Glauber, he says, “If we are going to understand coherence and the electromagnetic field of the laser- an electromagnetic field which is oscillating as it propagates through space. If we think back as to what it is that is actually the best picture of a laser beam of photons, it’s the quantum mechanics of the oscillating electromagnetic field. That question was very much an open and debated question in the early and mid-sixties. Schwinger published an important paper in the mid-sixties called “Brownian Motion of a Quantum Oscillator.” Feynman worked on it also and didn’t solve the problem to Lamb’s satisfaction. So Lamb said, “I’ll give it to you. You won’t be able to solve it wither, but something will come out of it.” In fact, we did get it, and it was a great way to get started in science.
Bromberg:Were you in contact with Glauber at this point?
Scully: Only in terms of his written article. I read his article, and of course I was in contact with Lamb every day. A dumb kid from Wyoming, I didn’t know that the Noble Prize physicist at Yale wasn’t there for me. Hey, I’m here, I’m a graduate student. So I would go see him, any time. I’d knock on the door and one might expect he’d say, “I’m busy. I don’t have time. Come back in two weeks.” But he always said, “Come on in”, and I would go and we would talk. I would take careful notes and work all night and come back the next day with one more brick for the project.
It was a wonderful collaboration, I was working hard and had some facility with mathematics and he was such a great seer. He understood physics so deeply. He didn’t have the patience to sit down and do these long calculations. But I did. I listened very carefully to what he said, and followed up on his ideas, and put a few of mine in. And I went to him every day. He never turned me away once. He put in, as I now recognize, an inordinate amount of time with me. Well, finally I got him to a point where he was interested in my results. He said one day — I’ll never forget — “I’m fascinated!” Usually the best we could get out of him was, “Nobody can argue with that.” So I finished my PhD in under three years. I stayed on as an instructor, and had a wonderful couple of years on the faculty at Yale.
Bromberg:Was anybody else that we should mention important for you at this point?
Scully:Oh yes. It was a great time to be at Yale. John Berdeen came to Yale and gave a series of lectures. And in fact it was Bardeen who made me feel that I had to do more theoretical physics. Because I was interested in low temperature and he was lecturing on many body theory. As a first year graduate student, it was way beyond my reach. But I didn’t know that. So I went to his lectures, and then I would go to see him after the lectures. And he was such a nice guy that again he would say, “Bring your lunch to my office and we’ll talk.” Lars Onsager was there. Gregory Breit. Yale at that time was just a Mecca.
Bromberg:I don’t think of Breit as easy to approach.
Scully:Well, Gregory Breit was a strange guy. Later in life, I had the opportunity to collaborate with Eugene Wigner. One night, I was saying something about Gregory Breit, and how I had coffee with him many times at Yale. And Eugene, who, you know, is the personification of politeness, said, “Well, I was Breit’s assistant at Wisconsin. One day I said to him, ‘No, Gregory, the point is…’ And, you know, he struck me, and knocked me to the ground. And then he said ‘I’m sorry. But you don’t tell me what the point is’.” Gregory Breit was that type of person. But if you didn’t let him intimidate you, it was great. He would work every night late by himself. A group of us would work late and go down to George and Harry’s, which was a coffee shop around half a mile from the physics department. One night Gregory Breit came in and we were arguing about a particular problem. So I said, “Look, there’s Gregory Breit, let’s go ask him.” The others said, “No, you can’t do that.” But I went over and said, “Professor Breit, would you join us. We’re arguing about a problem and we’d be just delighted if you would join us.” And he was delighted to join us.
That’s the way it was in those days. It was just a great place to be. Many of those people have gone on to do great things. John Reppy who went on to Cornell. C. T. Lane was the guru of the low temperature group. I enjoyed him immensely. David Lee (who got the Nobel Prize for his pioneering work in helium, was a graduate student at Yale.
Bromberg:Was it just physics in this world or did you ever move outside physics?
Scully:I went to chemistry a lot. Onsager was across the street doing chemistry. People didn’t talk to him because he was intimidating; very mathematical, and didn’t have much patience with people. I would go to his lectures and the chemists didn’t ask him questions. I always asked questions. I’ll never forget one day he made a strange statement. He said, “Crystals do not have periodic symmetry.” Nobody challenged him. So I said, “Why not. Seems to me like they do.” He said: “Think of this. Cleave the ends of a NaCl crystal. Then you have a positive charge here and a negative charge here, so you don’t have symmetry anymore.” I said, “Except for a trivial DC field, you have symmetry.” He said, “It’s only trivial after you’ve seen it!” I would go to his office and ask him questions often. It was an interaction that was more mathematical and technical. Whereas with Henry Margenau, the interaction was more philosophical. Do you remember Henry Margenau?
Bromberg: Sure. And I remember reading his book.
Scully:I loved Margenau. In fact, at one point I was so enamored by his lectures and his papers that I went to him and said, “I would like to do a project with you. I admire what you do.” He said, “Well, I’m really more involved with philosophical issues. And before you get involved in philosophical issues, I recommend you publish 15 papers on conventional quantum mechanics.”
Bromberg: Interesting! One thing I want to ask you before we end, and I’ll ask it now, is whether you keep any notebooks or other documentations from these early times, or any other times.
Scully:I have kept a lot of my calculations and correspondence. I’ve always thought that at some point I’d like to summarize some of these conversations with people like Lamb or like Bardeen. I’d like to try to bring some of the human side of those people out. This is theme of the book that I’m writing now with my son, who is a diesel mechanic and a writer. We are writing on the interaction between thermodynamics, with Sadi Carnot on the one hand, and quantum mechanics with Charlie Bernett on the other.
Bromberg:So you are going to cover two centuries?
Scully:Yes, and, in fact, guess what, the quantum eraser comes into the game. The Maxwell demon is exorcised in terms of the eraser. And I want to bring that out because Maxwell is right. Maxwell said, “In order to really get interested in science, what you should do is study the lives of scientists.” Study their ideas, and how they got those ideas, and that’s when it really becomes interesting. Who would ever have thought that Maxwell, the greatest physicist between Einstein and Newton, would have that deeply human feeling? I agree, one hundred percent.
Bromberg:And like you, Maxwell started out very interested in mechanics and how devices work.
Scully: You know Maxwell’s friend William Thomson (aka Lord Kelvin), who was older than Maxwell, was also interested in devices and was a great proponent of the transatlantic telegraph. He didn’t like Maxwell’s equations, because he didn’t have a model [for them]. Even though he himself was a great mathematician, a Second Wrangler at Cambridge.
Bromberg:And of course, Carnot was inspired by England’s use of the steam engine.
Scully:Yes. And Carnot said, “If you take the navy away from England, or if you take away the steam engine, you’ll do them more harm by taking away the steam engine.”
Bromberg:One of the things I want to ask you is: you are at Yale. Are you already talking with Lamb about the problem of measurement?
Scully:Very good question! Things happened very fast. After we knocked the laser problem, we went to the APS, on some occasion, and presented it, and I met a wonderful physicist named Mel Lax from Bell Labs. Well, Mel Lax later turned out to be one of my heroes, but at that time, he and Lamb got into an argument on the floor of the New York meeting, of the APS. There Lax said, “You can’t get the results that you and Scully have done and say that it means anything, because all you’ve done is derived the density matrix of the radiation field. In order to interpret it physically, you have to use my regression theorem.”
Lamb said, “We will take this to the pages of the Physical Review.” So we went back to Yale and Lamb said, “Here’s the kind of model that we’ll use, and you go and solve this.” This is how we approach the interpretation of quantum mechanics. How do you use the kind of mathematics that we used to say something about the spectral content of the laser? It’s back to the Bohr- Townes debate. The laser line is very narrow, but it’s not infinitely narrow. And how do you understand the fundamental question of what it means to have some finite line width? This was ’67-68. And I went away and came back with the answer. It was “Quantum Theory of the Laser II.” [ M.O. Scully and W.E. Lamb, Jr., “Quantum Theory of an Optical Maser. II. Spectral Profile,” Phys. Rev. 166 (1968), 246.]
Bromberg:Now, before that, you were at this Puerto Rico meeting . Was Lax at that also?
Scully:Yes, Lax was there. And there were the three main schools of laser physics: Lamb, Lax and Hermann Haken. And at that meeting we presented our result. That is, we had the quantum theory, and we had the statistics. We showed how we go from photons to classical electro-magnetic waves. We did it with what would loosely be called Schrondinger’s approach to quantum mechanics, the Schronginder picture. Lax came from a different perspective and used an operator formalism, which was essentially developed by himself, and others, but it was Heisenberg’s point of view.
Bromberg:I should tell the tape that the book we are talking about is Sargent, Lamb and Scully, Laser Physics. [ M. Sargent III, M.O. Scully, and W.E. Lamb, Jr., Laser Physics, (Reading, MA: Addison- Wesley, 1974)]. And the chapter is chapter 18, “Quantum Laser Theory and Measurement.”
Scully:Yeah. This is a fun book that Murray Sargent and I wrote. Murray was a student of Lamb’s, and he was a friend of mine, and in some sense he was Lamb’s favorite student at that time. He was a flamboyant kid, very handsome young man. He liked the same sort of things Lamb did. And so after I left Yale and went to MIT, they called me from Arizona to see if I’d like to help them set up the Optical Science Center. I immediately called Murray, and he came with me. I gave a series of lectures in Arizona, which Murray then transcribed and it turned into this book.
Bromberg:Now, let’s deal for a moment with the MIT interregnum. What took you there?
Scully:I was at Yale for 2 years after I got my degree, and then it just seemed it was time to move on. And there were some interesting people at MIT at that time. Charles Townes, and Ali Javan, and others, but those two in particular. And then there was a great group of people up at Harvard: Julian Schwinger, Roy Glauber, and Paul Martin. And so it was a natural. They made me an offer to come there as Assistant Professor. So I went in the fall of ’68. And I was there one year and I got a nice offer from Johns Hopkins. MIT promoted me and I stayed. But then the next year I got the call from Arizona. They told me, “Come here, hire Murray Sargent, hire Willis Lamb and we’ll give you all the money you need.” It was kind of crazy to leave MIT and all those good people, but Arizona was an exciting opportunity.
Vicki Weisskopf at MIT was so wonderful. He was my hero. In fact, I got my early promotion because of Vicki. I went to him one day and said that I didn’t understand stimulated emission. How come we say that radiation goes in a forward direction when there is stimulated emission? When you look at it, it is dipole emission and dipoles radiate in a forward direction and a backward direction. And Weisskopf said, “Ah, that’s a very good question. Let’s talk about it again.” That weekend, he called me at home, and he said, “I’ve been thinking about your problem, and you must answer that question.” So I got busy and I figured out that it had to do with Poynting vector and the interference between the incident field and the radiated field. So I went to him and said, “It’s the Poynting vector.” And he said, “Ach, that’s anschaulich.”
Bromberg:We were talking about your getting over to Harvard. Whether people like Glauber and Schwinger were important interactors.
Scully:Right. I would go over and talk to people like Glauber and Martin and Schwinger. I met Schwinger only by bumping into him and going to his lectures. He was unapproachable in those times. And I told him, “Oh, I used your Journal of Mathematical Physics 1960 article on Quantum Brownian Motion Oscillators, and I applied it to Josephson radiation. And he said, “Oh, that’s great. You have the whole field to yourself. Nobody else is working on it.” That was typical of my interaction with Schwinger.
Glauber was a friendly, avuncular kind of guy. He set up a dinner one night with my wife and his wife and a young guy named Steven Weinberg and his wife. Glauber was that kind of guy. Over the years, I’ve come to admire him immensely. Later Schwinger became a frequent guest in our home. He spent a lot of time with me in Munich and in New Mexico. We had great fun skiing and visiting at our ranch.
Bromberg:You’ve collaborated with so many people. I’ve wondered at one point if that had anything to do with the scope, the range of problems you’ve worked on.
Scully:Oh absolutely. You are very perceptive. For example, what is this crazy quantum physicist doing looking for anthrax? Well, after 9/11, when all of us felt depressed, and my son who is an American Airlines pilot, had some anxious moments. Well, I wanted to do something, and I got to thinking that if we could make a real time laser detector for anthrax, it would be useful. But I didn’t know anything about it, so I began calling people, and over a period of 6 months or so, I learned a great deal just by talking to everyone I could talk with. I pestered them to death and then realized we could use a laser to find the molecular marker that is in anthrax. We would have to develop a new kind of laser spectroscopy based on the Raman detection of spores, which was pioneered here at Princeton by Tom Spiro. So I got in touch with Warren and Herschel Raditz and started a collaboration and that’s how I happened be here.
You can learn so much faster, and it’s so much more fun to go skiing with Julian Schwinger and pick his brain on the lift, to have a chance to argue with Ed Jaynes, and to have supper with Eugene Winger and find out about his life. “Eugene, why did they deny you tenure at Princeton?”
“Because they didn’t think I was a good physicist,” says he. And this kind of Maxwellian approach — you learn the people and you learn from the people — is so much fun. And they all want to talk, but mostly they’re kind of bashful and they don’t barge in and say “Hey, how about we have lunch together and talk about your latest paper.”
Bromberg:Before we leave the sixties, Bell at this point was publishing his paper, and of course Bohm had published about 12 years earlier. Was that kind of thing making any impression?
Scully:A negative impression. It wasn’t somehow honorable, in Lamb’s view and the view of many others, to talk about the foundations of quantum mechanics divorced from Gedanken or real experiments. And the great genius of David Bohm, whom I’ve come to admire immensely, although I am one of his strongest critics. And John Bell, also most of us are admirers of Bell’s work. But at the time, it seemed unlikely that this kind of thing would lead to anything interesting. The EPR paradox had been around for so long. And Niels Bohr had made his pronouncements, but Bohr’s reply to EPR didn’t really strike to the heart of the matter. So it was something that we thought wasn’t likely to lead to anything.
It was only after we had been in the foundations of quantum mechanics business for five or six years that it really became interesting. We were taken with Wigner’s point of view...Wigner was always thinking of little models and experiments. For example, he thought about the Stern-Gerlach experiment and he came up with this idea: You separate the beams, you put them back together. Is it the same? He said, “Yes, it is, because of time reversal.” Lamb looked at it and said, “No, it’s not, because of the spreading of the wave packet.” So I got interested with Julian Schwinger, and we did solve it. We showed that both were right, and both were wrong. And it was in that sense, solving very specific problems, always tied to a specific experiment, that we got into the business to a point that we said, “Oh, now I see how beautiful this idea of John Bell’s is. Now I see how to make contact with David Bohm.” So it was coming in the back door, after we had gotten quite a bit downstream from where they were.
Bromberg:And would you say that Lamb’s operational approach and Wigner’s were similar then?
Scully:That’s an interesting question. My off-the-cuff answer is that there is a spectrum here. Lamb’s at one end of the spectrum, very operational. Did the calculation for the Lamb shift in great detail! Wonderful, wonderful physicist with a strong engineering bent. During the war he worked on radar, and was always a very practical guy. Wigner was a very great mathematical physicist, but don’t forget, Wigner designed some of the first nuclear reactors. He was a strong practical engineering kind of guy when the need arose. But Wigner was more philosophical.
Bromberg:He started out as an engineer, as I remember.
Scully:Yes. His father told him, “You will never get a job as a physicist.” So he started training as a chemical engineer. But all along the way, he was seeing interesting questions and doing fundamental physics papers. Eugene was perhaps more towards the philosophical end of the spectrum. As soon as John Bell came out with his profound ideas, Wigner showed how to re-interpret that from the point of view we call counterfactual. That treatment is in our book on quantum optics [Marlan O. Scully and M. Suhail Zubairy, Quantum Optics, Cambridge University Press, 1997]. Chapter 18 is on the EPR paradox, and on Bell’s inequality from Wigner’s perspective.
Julian Schwinger was another engineer-oriented guy. Once I said to Julian that I wasn’t a great fan of string theory because I guessed I was too much of an engineer. Julian said, “It’s is not possible to be too much of an engineer.” Do you want a footnote to that? Right now we are sending an article to Physical Review Letters, in which we apply the mathematics we get from quantum chromodynamics, called dimensional scaling, to an old problem Bohr tried to do many years ago, in 1913, and didn’t succeed. But we, together with Dudley Herschbach, the Nobel Prize winning chemist physicist, are applying those new techniques to Bohr’s old problems. So anytime I have said, “Oh, that’s not interesting. It’s too mathematical.” “It’s too philosophical.” It always comes back to haunt me. It always turns out to be more interesting than I thought. So I end up spending months and months on the mathematics of particle physics, or on Bell inequalities. Serves me right for being narrow-minded.
Bromberg:One thing we left out, before we get to Arizona, is the interaction with Jaynes. And there was this celebrated bet, I think at the 1966 Rochester meeting between Lamb and Jaynes.
That may be right. I don’t remember the exact timing. Anyway, there was this great quote from Jaynes, “Physics goes forward on the shoulder of doubters, not believers. And I doubt that quantum electrodynamics is necessary.” And then he went on to explain his interesting ideas about semi-classical theory, neoclassical theory, in which the atoms are quantized, the electromagnetic field is still treated according to Maxwell’s equations. I was fascinated by his ideas. It was the antithesis of my point of view, because Lamb and I had been working hard to understand the classical-quantum interface of atoms, photons, and fields. So I had a strong sense of how the mathematics went and how the philosophy went. Because of literally days and days of working with Lamb, and talking it over and over with him. I was sure that Jaynes was wrong. So I said to Lamb, who as at the conference, “What did you think of Jaynes’ talk?” He said, “Jaynes is a genius.” He was taken with Jaynes’ point of view. But not a year later, he was saying, “Jaynes is wrong minded.”
I was a great fan of Jaynes from the very first time I heard him talk. I completely disagreed with what he was saying. But he was so forceful and so clear in his vision, his perspective, that I just loved him. That’s always been my philosophy. I’m not so interested in hearing boring, well-laid arguments which are, in words of Pauli, not even wrong. I would much rather hear interesting arguments, which are probably not quite right, but are going to lead to other interesting results. And I’ve spent a good fraction of my career based on ideas that have come from people like Ed Jaynes and Willis Lamb and Julian Schwinger and many of my excellent students. But Jaynes, back in seventies, was a great hero, a counter-culture kind of guy.
You know the story of Jaynes. He didn’t get promoted at Stanford because of his unorthodox ideas on statistical mechanics. I heard from various sources that Felix Bloch didn’t like what Jaynes was doing in statistical mechanics. Jaynes had the point of view that information was the way to go. In this, Jaynes was absolutely right. But some didn’t like it. They thought that statistical mechanics was a well-honed machine and that we should be teaching students conventional statistical mechanics. So then, Jaynes came to St. Louis. A good person to check this story would be Joe Eberly at Rochester. He got his Ph.D. from Jaynes at Stanford and he would surely have insights into this. I would like to know what he says.
Bromberg:So Jaynes, he is really fascinating from reading his articles, and I am curious what he was like, and what he was like to interact with.
Scully:Well, he was very picky, no- nonsense, stand-up kind of guy. I locked horns with him over and over again. And I always enjoyed him, always tried to be friendly, and never intentionally gave him a punch. But I did. I would simply state my case, and he would regard it as arguing against him personally. For example, I was invited by Physics Today to write an article on the concept of the photon. [M.O. Scully and M. Sargent III, “The Concept of the Photon,” Physics Today (March 1972), p. 38] By the way, just last year, I wrote one called “The Concept of Photon Revisited.” I’ll get you that. And in this article, I mentioned that if you take Jaynes’ point of view, then the commutation relations for the electromagnetic field are violated. They can be compromised. If you do that, then the uncertainty relations for the electromagnetic field are out the window. That was a sidebar in our article.
As you correctly pointed out [draft by J.L. Bromberg, “The Micromaser as a Philosophic Instrument], Jaynes hated that. He came back at the Rochester meeting with this “The honor of the lady is still intact (not violated).” [E.T. Jaynes, “Survey of the Present Status of Neoclassical Radiation Theory,” in Coherence and Quantum Optics: Proceedings of the 1972 Conference on Coherence and Quantum Optics, eds. Leonard Mandel and Emil Wolf, (Plenum Press, 1973), 35-81] He came on so strong at this meeting, which was probably 1970. ‘66 was his first talk. Little did I dream, after ‘66, that his next pronouncement would figure on work that I had done and that he would be giving me such a scolding in Public.
And then I decided, O.K., I’ve got to get serious about this. So I looked for ways to show exactly what I was doing e.g. why I was right and he was wrong. So I published some papers which had to do with quantum beats. And that’s the first chapter in the Quantum Optics book. But the idea is, if you have an atom…let me use the board. If you have an atom, with two upper levels and one lower level, then radiation from the upper levels to the lower level shows quantum beats. I’m going to give you our Quantum Optics book. It tells the story of how it is that the quantum beats business sheds light on the semi-classical vs. the quantum theory. So here we show in pp. 16 - 18, that if you have two upper levels and they decay, then you will see a beat note in a photo-detector. Instead of seeing just a steady steam of photo counts, you will now see a modulation in the number of photo counts per second. That’s the beautiful quantum beat idea, which George Series and others pioneered in the sixties. Well, you would think you might also see that if you had one upper level and two lower levels, because you have two colors, but you do not. However from Jaynes’ semi-classical point of view, you would see beats. So I published a paper in which we pointed that out, and Jaynes immediately took this to heart, and later (around ’79), he thought that he could show that by manipulating the lower levels after the photons were emitted, that he could make the beats go away or not. And he was wrong. He wrote this famous “this isn’t science, this is necromancy.” It’s black magic. Do you remember that quote?
Bromberg:Possibly. In a conference collection from 1980 [Asim 0. Barut, ed., Foundations of Radiation Theory and Quantum Electrodynamics, Plenum Press, 1980)], there’s an article by him on beats and an article by you on beats. It may be in that.
Scully:I was thinking about the quantum eraser at that time. And he was sort of thinking about that too. But typical Jaynes, he had these beautiful ideas, but he got it wrong. But interestingly wrong. I have a Scientific American article with B-G. Englert and Herbert Walther, in which we quote this wonderful Jaynesian remark about black magic. [“The Duality in Matter and Light” Vol. 291 Scientific American (December 1994) 56-61] The point was that Jaynes thought that you could shine microwave radiation on the ground state doublet after it emitted radiation — in this lambda type atom [two closely spaced lower levels] — and that you could make beats come and go by massaging the atom. And that’s half right. It’s not enough, however, to just shine radiation on the atom. You must make an observation. And it’s that combination of preparation, shining light on the atom, plus observation, that leads to quantum eraser. And in a sense then, it comes back to why I love Ed Jaynes. He just was so stimulating and made these strong statements that led us to work hard. He stimulated us and made us think harder.
Bromberg:Shall we go now to Arizona and that Optical Science Center. I’m really interested to know how it was set up and by whom. And why there was so much applied work… free- electron lasers and X-ray lasers and so forth.
Scully:Yeah. Gyroscopes. As I mentioned earlier, I was at MIT and Arizona called me. The main contact that I had there was a physicist named Steve Jacobs. Steve Jacobs was a very interesting character. He was a good scientist and optical person; worked with Gordon Gould. And was involved in making the first, I think it was, sodium laser, back in the early days when nothing much but ruby had lased. Maybe the second laser, maybe the third. He went then to Arizona and invited me to come out. So I went out for a visit, enjoyed my interactions, and went back to MIT. Then he went to MIT, and suggested we go down to Washington, and talk to people in Washington about this new Optical Science Center. Aden Meinel was the one who had made the Optical Sciences Center work. He was an astronomer, discovered the Meinel bands of nitrogen, and built Kitt Peak, by the way. He then was contacted by the Air Force and they asked him if he would work on the problem of optical resolution. Well, back in those days, satellite reconnaissance was developing and it was very difficult to get scientists who knew enough optics to help the Air Force in their mission. And so the thought was, perhaps we should have another Rochester. Rochester was based on optics coming from Kodak i.e. a very different perspective. What if we had a group that was focused on big optics. Big telescopes for astronomy and perhaps big systems for satellite applications. So Aden got the money together to build the Optical Science Center.
Adam was a very inventive guy. You couldn’t use government contract money to build a building. Therefore what he did was to go to bank and borrow X million dollars to build a building at the University of Arizona, with the agreement with the Air Force that they would lease that building, and the lease could be structured so that in a few years, it would pay off the loan. That’s the kind of guy he was. Then after my visit, Jacob came to MIT and said, “Let’s go down to Washington and talk to people and see if we can get some support.”
Bromberg:Was that the Air Force Office of Scientific Research?
Scully:That’s right. After we were there for a while and were about to leave, I said, “Why don’t we go over to the NSF and see if we can get a million dollars.” And Jacobs said, “That’s what I like about you, Scully. You think big.” I said, “I thought you liked me because of my personality!” He said “No” and he was serious. So at that point I realized that he was a quality person. He was so straightforward. So I took a leave of absence from MIT for a year and went to Arizona. They offered me a job as a full professor at the tender age of 29 so I was interested. Then I got a windfall in the form of a Guggenheim, quite a nice surprise. So I took the Guggenheim to go back to MIT and finish off my students and my job there.
I had outstanding students. One young man was named Patrick Lee, now a professor at MIT, superconductor theorist. Another was Roy Lang, who became vice-president of Nippon Electric in Japan. He was half-Japanese, half English. And there were other wonderful young people.
I returned to Arizona in ‘71, just at the time when Aden Meinel was retiring. He wanted to go back into science. He had built the place. He didn’t want to be Director anymore. We had the building. We had everything. He called me in one day and he said, “Would you like to be Director?” And I said, “No, but I would like to be Chair of the Committee that chooses the new Director.” So I was Chair of the Committee that called Peter Franken. At the same time, Murray Sargent and I were talking to Willis Lamb. Lamb was very close to both of us. My youngest son, Steve Willis Scully, once said to Lamb, “How are your children?” Lamb said, “Well, Steve, I don’t have any children. My graduate students are my children.” And that’s really the way it was.
So Lamb came out to be with Murray and me. And Peter Franken was a big help. It turned out that Franken and Lamb were friends from years gone by, which we didn’t know at the time, but were delighted to learn. So that’s how we brought Lamb, the big Nobel Prize winner, to Arizona. The first Nobel Prize winner at Arizona. It was ‘73 or ‘74 by the time we got Willis out there. And we did a Festschrift for Willis. Dirk Ter Haar and I were co-editors.
Willis didn’t like these ideas about EPR. By that time, I had gotten interested. We figured out how to make a mathematically consistent treatment, which explained part of the problem with EPR. There’s really no problem. We showed how the density matrix enabled us to make this clear. This is in a paper with Cantrell. He was at Los Alamos and I was consulting for Los Alamos. He’d come down and spend time with me. So we wrote the EPR article for the Lamb Festchrift.
Bromberg:I have a question at this point about all the work you were doing at Kirtland Air Force on the X-ray laser, the free-electron laser and so forth.
Scully:Yes, and it was a manifestation of my mindset. I have always felt that part of scientist’s opportunity, perhaps of his obligation, is to try to use science to benefit society, mankind, and his nation. I remember at the University of Wyoming, where I was for a couple of years, had a great quote above the engineering building I walked to each morning…forty below zero… and on the top of the building it said “strive on, for the control of nature is won not given.” One of my teachers, Bill Rosenthal, a good physicist said, “We’re not trying to control nature. We just want to understand it.” And I thought, “Well, what’s wrong with doing both?”
When I got to Yale, I had the good fortune to work with Lamb, who was doing both. He was building the theory for new devices, like developing the theory for better laser gyroscopes. So when I got to Arizona, it was time to do experiments, and to build real-world things. For example, we were working with companies in California to build laser gyroscopes. One of my students, Dana Anderson, now a famous professor at JILA in Boulder, did his thesis with me and then went to California to build better optical cavities. He started his career that way.
But then, Kirtland Air Force Base physicist, Pete Avizoniz, came to us and said, “Will you help us? We have a lot of problems involving lasers and optics and quantum mechanics and chemistry. Would you be sort of a house theorist?” So I thought, “Great, good idea.” So I did.
Bromberg:If the Air Force is giving the Optical Sciences Center money. You’d think they’d be thinking of getting help with their optical problems.
Scully:Yes and no. You see, when we started talking to the people in Arizona, this was in ‘67, ‘68, right at the time I came to MIT, really. In the late sixties, money was just there. You didn’t have to worry about getting money. When I went to MIT, they gave me a very generous grant. I just showed up one day and the money was there. I also got to share an office with John Slater. But the trouble hit in 1969, something showed up called the Mansfield amendment. This was one of the worst things to happen to this nation, and to our defense forces. They said, “Well, if you can’t fit it on the wing of an airplane, or make a better machine gun with it, we won’t fund you out of DOD.” So people were losing their funding. Everyone was going belly-up. People were losing their jobs in California in the aerospace industry. It was a kind of depression in Physics.
At the same time, I was very supportive of America. Vietnam was a terrible situation, and I wanted to help my country. I am not smart enough to know whether we should be in Vietnam or Iraq or Afghanistan. All I know is that I have an obligation as an American to help when I’m asked. I was asked. Especially in view of the times and the fact that during the Cold War it seemed very likely that we would have a nuclear or missile attack on the US. If we could build lasers to defend American cities from missiles, that would be important. What a great idea. Well, it turned out that it wasn’t practical. But it looked like it could work, and someday it will.
Bromberg:There was a lot of debate about that idea. Was there debate this early?
Scully:People weren’t arguing so much that we couldn’t do it. They were arguing more that we shouldn’t do it. Because it would be destabilizing. If we did it, then the Soviets would feel that it’s another step in the arms race, and that’s an argument that I never understood. I was more in tune with Edward Teller, who felt that if we could do something that would provide a shield, of even some cities, it should be done. What if a renegade submarine officer in the Pacific sent off a nuclear missile at San Francisco? If we could take that out with a laser…even if we couldn’t take out a thousand, if we could take out one, wouldn’t that be a good thing to do. We thought we could do it and still think we can. But we were hampered by atmospheric pressure fluctuations. We couldn’t control the laser beams well enough then. We can now.
Bromberg:Were those the X-ray laser papers?
Scully:No, the papers were on the free electron lasers and high-power lasers. The X-ray business was something else. That was work I was doing for the Army. Bill Louisell and Mel Lax and I went to Redstone Arsenal and worked with lead scientist Bill McKnight. He wanted to do work on the X-ray laser. So I came up with this idea for a charge exchange X-ray laser that was eventually patented. We worked on that one summer. Generated 3 or 4 papers, but it was never viewed as a weapon. Simply that Bill McKnight wanted us to do it, and he was the boss, and it was interesting.
Bromberg:The bright historian at MIT, David Kaiser, is saying that what physicists do to some extent, depends upon how many graduate students they have to keep busy. Does that idea have any relevance to your work?
Scully:Just the opposite. I always picked problems because I thought they were interesting or important or because I thought there was a potential windfall there. I’ve always selected graduate students carefully. Even then I only work with about half of those I take. I assign the other students to work with a post-doc of another professor. So for these students each of them will have their own post-doc, frequently a post-doc and a faculty member. I have a multi-million dollar budget. And I’m funding dozens of faculty members at Texas A&M and at Princeton. So I fund many graduate students. But the graduate students I work with closely are separate. I generally pick one or two. Maybe you’ve heard of Mikhail Lukin. He’s at Harvard now. He is an example of a student I worked closely with. Wolfgang Schleich in Germany is another.
Scully:The Lene Han Harvard group used a Bose condensate to slow light. We, in Texas (including Lukin), were able to do it with hot atoms. Lukin is now an Assistant Professor at Harvard has just been offered an Associate Professorship at Stanford with tenure. And now Harvard is looking to make him maybe a full Professor. That’s the kind of guy that I feel that I can help. I’m not a very popular thesis advisor because I work hard, and I call my students frequently. They say they’re glad when they see my wife coming, because they know I’m going to take her out to dinner and take the night off. And that’s fine, but if they have the “right stuff,” I can help them. So back to this person who says that our work is driven by the number of graduate students we have to keep busy. Just the opposite. I have plenty of money. I can’t find enough students who I want to work closely with.
Bromberg:Something else I want to ask you about is Herschel Pilloff and the Office of Naval Research. Because I think of him as this prime supporter of quantum optics. So I wonder if he had any role in your history.
Scully:Absolutely. What a great question. He was my mentor and supporter for 30 years. I’ll tell you some funny stories about him. He’s retired and lives in Colorado. I was just at his house a few weeks ago. And I love the guy, as a scientist, as a human being, and he has a wonderful family. He has two sons and a daughter, and one son, Mark Pilloff, was an A+ student at Cornell. Mark and I even did a paper together when he was an undergraduate. Then he went to Berkeley, A+ at Berkeley. He went into string theory, got disillusioned, crashed and burned. He didn’t want to finish his Ph.D. So I heard about this and I called him and said, “Mark, you come to me in Texas. In one year, you’ll have your Ph.D.” So he did. For one year he followed me around the world, and he just got his Ph.D. this past May from U.C. Berkeley. I was an external faculty advisor at Berkeley so that I could do this with Mark. And so Herschel Pilloff and Herschel Pilloff’s family are some of my favorite people.
Bromberg: Well you’re in Arizona now, in the mid-seventies. Does he contact you and say, “I’d love to give you some money”? Or, how did you get to know him?
Scully:Well, it’s been so long ago that I will have to try to construct what I think was the most likely scenario. I never waited for anyone to come to me and offer me money. I mean, if I had an idea, I’d just write a proposal and send it off to the agencies. Last year, my budget was several million. I’ve never had problems with money. This year I have another big grant coming on the anthrax project. So probably what happened is that I wrote up a proposal and send it to Herschell Pilloff and he began funding us. Pilloff funded me from seventies through the nineties, when he retired.
Bromberg:Was there any particular part of your work that he was more interested than other parts? Or he just said, “I like what you’re doing. Keep doing it.”
Scully:Well, no. He would come to all of our conferences. Jacobs and I would run these Snowbird winter conferences. Hersch and I would run summer schools.
Bromberg:Was this the Physics of Quantum Electronic summer schools?
Bromberg: Were the conferences connected with skiing?
Scully:Yes. We meet January 2-6 this year in Snowbird. Steve Jacobs, Pete Avizonis and I started them. And sometime I have to tell you about the Golden Fleece award that Senator Proxmire tried to give us, but couldn’t make stick. We did so much science that nobody could criticize us. But he said, “Well, I’m going to give you a reprimand anyway.”
But Pilloff. Well, Hersch and I would run schools together in the summer, as well as his participation in the winter. So it was always the case that we had a strong relationship. I’d tell him what I was doing. And he would say, “So you are going to make a laser without population inversion. You should be using rubidium, and diode lasers.” Then I would say, No, I want to use sodium and dye lasers.” He would reply, “I think you should do this and here’s why.” And he would give his arguments. We would always come to a conclusion that was based on solid science. Other time he might call me up and say, “I have an idea for laser gyroscopes.” And I’d say, “That’s interesting but I don’t think it would work.” We’d go back and forth for weeks. On that particular occasion, I think he finally agreed with me.
Bromberg: So it was more like a collaboration than a Program Manager.
Scully:Right. He was the best kind of program manager. He understood things deeply. I brought him good results every year: lasing without inversion, ultra-slow light, new magnetometers, new gyroscopes, new quantum-theoretic devices, etc. We would make sure that he knew what we were doing. And we delivered on what we proposed to do.
Bromberg:Everything you’ve mentioned so far is a device. When you were doing something like the EPR analysis, would you do that for the NSF then?
Scully:No. Herschell Pilloff would support that. For example, take the quantum eraser. That was a very philosophical work. But it led to new ways of storing quantum information and new quantum imaging devices. Better microscopes, that goes beyond the Rayleigh limits, as I was mentioning earlier. So yes indeed, the interference between ideas, philosophy, devices, and applied physics is one that is very rich. However, it, unfortunately, is not appreciated because we don’t teach students what a great thrill it is to invent as well as discover. We don’t teach them that doing the calculation and then the experiment and having them match is a great thrill; but writing a patent is as much fun as writing a Phys. Rev. Letter.
Bromberg:I do want to find out about this seminar. Because of some of your papers, for example on the quantum eraser, you say that these ideas took shape at a seminar in Arizona at the University of Arizona.
Scully:That was an internal seminar series that sprang up from an unusual group of people at Arizona, including Willis Lamb. It was once a week seminar at the University. But then there were summer seminars and workshops to which I also refer in some of my papers. Ideas on Bell inequalities (e.g. local versus nonlocal) also came from that meeting.
Bromberg:What I’m thinking of was something that was jointly the Department of Philosophy, the Department of Mathematics, and the Department of Physics. I think Shea, Cantrell, and Lamb were there. Did you suddenly start to read a lot of old papers? What was going there?
Scully:Right. We were arguing about things like the EPR paradox, the foundations of quantum mechanics, semi classical theory, Jaynesian quantum electrodynamics. This was a weekly invited seminar sequence that went over the period of a year. It was exciting with people like Wes Salmon, who was from the philosophy department at the University of Indiana and Hanno Rund, who was the head of the math department, a really excellent mathematician and interested in physics. Of course Willis and all of the guys from my group, who were interested. Cy Cantrell, who came from Los Alamos, and many others.
Bromberg:Why did you start on that? Was something going on in the late seventies that all of a sudden, you guys decided to talk about these things?
Scully:Well, I think we were always talking about these things. For example, Lamb would come to our house for Thanksgiving. We used to have a group of 40 people out to my ranch in Arizona for Thanksgiving. The Jacobs-Scully Thanksgiving. And one time I said to Lamb, “Look, I think the application of quantum mechanics to a single entity is quite feasible. You don’t need an ensemble.” Schroedinger and others had always said that you have to have an ensemble. But, I said to Willis, “It’s not true. I can apply quantum mechanics to one atom or one neutron and have betting odds. A gamma ray scatters off an atom, scatters off a neutron. And I’m able to say with a certain probability, what’s the betting odds that it’s going to go in this direction. But within that aspect of the game, I can do quantum mechanics for one entity.” Then Lamb said, “Well, if that gives you comfort, go ahead.”
So these kinds of arguments. Even when we were in the most applied, laser gyroscope kind of seminar, we would go to lunch and argue, “How can I apply this laser gyroscope to measuring magnetic gravity, how can I use it to test general relativity?” There was always excitement and interest on every level, on every problem. On fundamental issues, or trying to make a laser gyroscope that wouldn’t lock up, that would measure slower and slower radiation rates. We didn’t think that there was any big difference between fundamental and applied problems, really. They were all just neat problems.
But of course, many people didn’t agree with that. For example, Prigogine. I was invited to give lectures in Austin in the mid- seventies. And I was lecturing on the free-electron laser, which we had just shown operates according to the classical laws contrary to the then often voiced wisdom from FEL hero John Madey. There is nothing quantum mechanical about the free-electron laser. We were the first to show that. So it was exciting. At that same time we were showing that the laser gyro could be re-configured and a large laser gyro could make gravity measurements. Prigogine sat next to me at dinner one night and said, “Scully, you’re a great problem solver.” And I knew that was a thinly-veiled insult and what he meant was, “You should be thinking about the deep questions.” Like the nature of time. That’s what he thought about all of his life. He thought that somehow statistical mechanics was going to give us a deeper insight into connection between entropy and time. He would say, “I would like to be ten years younger, but I cannot. I do not believe that irreversibility is only in my mind.”
I forgot what you asked that triggered me off on this, but the point is that we in my group, and the Lamb group, others at Arizona, MIT, and the Max Planck Institute like Julian Schwinger; always thought that solving problems was fun. We would find as much satisfaction in solving problems dealing with the foundation of quantum mechanics as inventing a new kind of X-ray laser. And that’s still the way it is.
Bromberg:When you went to Europe, and started working in both Garching and New Mexico. Did you find a different way of doing things, or are they also problem solvers?
Scully: Yeah, yeah. I really enjoyed the people in Garching. One of my favorite post-docs was Pierre Meystre. He came to me in Arizona from Switzerland, paid by the Swiss government, and worked with us for, gosh, three, four, five years. And then he went to Garching to work with Herbert Walther. And came and said to me, “This is a really great place. You’ve got to come and spend some time.” He was the connection. So I went to Garching for a summer and it was great. So I accepted a position in Garching.
At that time, I had three boys, who were growing into active- hyperactive-young men. And I frequently wasn’t home when I needed to be home. We had a small, forty-acre farm outside of Tucson. And they wanted a more rural experience. They really wanted a ranch. And I went around the country and found a ranch near Boulder, and got a job offer from Boulder, but somehow, I never did feel right about it. Simultaneously, the people at Los Alamos and Kirtland said, “Why don’t you come to New Mexico and build something at the University of New Mexico (with the understanding that I would be allowed to spend half of my time in New Mexico and half of my time in Garching). I loved Germany and the Germans. I ended up getting probably the best kind of working environment that was available anywhere in the world at the Max Planck Institute. It was fantastic.
Bromberg:And did they have a different way of doing physics? I am hypothesizing that Americans and Europeans do physics differently, but I may just be wrong.
Scully:No, you’re right. It is very different. In the U.S., I was on my own. I could do anything I wanted that I could do on my own or find money to support. And since I never had trouble finding money that was OK. But in Munich, they bought me as Head of the laser theory group. They gave me nice budget, and I bought my US students over with me and my German students like the now famous Wolfgang Schleich came back to the US with me. I had collaborators like Herbert Walther, one of the great men in quantum optics. And I not only didn’t have to find money, they actively discouraged people from trying to find money. The Max Planck Institute gave us everything we needed. So to spend our time out looking for money was in some sense to deflect our energies from what we should be doing.
Bromberg:Isn’t it indeed a deflection? The physicists have become entrepreneurs and have to do money-raising?
Scully:I like to say, if I’m teaching freshman physics, it takes a lot of energy and a lot of time to prepare these lectures. It also takes energy and time to go find funding. But it’s no big deal. (Telephone interruption) The American system has the problem that you have to find the funding to do what you want. That’s the bad news. But the good news is that you can find the funding. In Germany, if you are not the lead professor, there’s no place to go. There is one place: the Deutscheforschungsgemeinschaft. It’s like the NSF. They don’t have ONR, and AFOSR, and NIH, and a dozen places to go for money.
I think the American system is arguably better…but if you are in a favored position in Germany, as in these Max Planck Institutes, that’s probably the best. And that’s what I had. I had the best of both worlds. Over there I had a great theory group, and at the same time we were doing experiments at American universities. As you know, graduate schools in America are excellent. Graduate school in Munich was fine, but the Max Planck Institute was really the best. And that’s the long and short of it. I really appreciate the universities, because I can work 120 hours a week and nobody cares. And in Munich I could work for 120 hours a week, but it’s just all science. I didn’t prepare a proposal. Every other year, I have to go to Munich and give a 30 min presentation on what I was doing. There would be people like Norman Ramsey and Claude Cohen-Tannoudji reviewing what we have to say.
Here, I decided to do this anthrax experiment. So I went to DARPA, told them what we were doing, and they bought in a group of people and they said, “You can’t do that. Here’s why.” We defended our ground. And they said, “OK, come back next week.” We came back next week. We did this for several times and finally they said, “Ok, here’s a million dollars. Go try it.” We tried it, it looked interesting, and then they said, “OK, here are the new rules. Now the ante is up. It’s 10 million dollars. But you’ve got to detect anthrax in a cloud a mile away. Can you do that?” So we get into arguments about why we think we can. They bring in people who say we can’t. We say, “Well, you’re right. We missed that.” We go back and fix it and come back and say, “Now we can.” They say “OK.” So I go home and buy the equipment and then I find out that you can’t get people in Texas to do these experiments, because they’re very subtle experiments. There are only 2 or 3 places in the world where people know how to do these very tricky femto-second molecular spectroscopy experiments, and Princeton is one of them.
Bromberg:And so that’s why you’re here?
Scully:Right. So I called these guys, and they said, fine, why don’t you come to Princeton? We’ll make you a visiting professor of chemistry.
Bromberg:Here’s a totally unrelated question but one I’m curious about. You’ve collaborated with everybody I can think of, but not with Mandel.
Scully:I never collaborated with Len because his philosophy of science and mine are quite different. People like Yanhua Shih and Roy Glauber might also speak to that issue. He was very helpful if I needed a letter for a university. Typically universities write not just to your friends, but to people you haven’t collaborated with, and he helped me and supported me. He had a deep human side. In writing his bio for the National Academy of Science, I found out that his kids had moved from London to Rochester, and meanwhile he got a call to Paris. It would have been important for his career. But his kids needed to stay in one place, so he put that opportunity aside and stayed with his family in Rochester. That speaks well for Len.
Bromberg:Speaking of Paris, what was the relation between the group under Walther and the Haroche group? Because you were doing some rather similar things in the eighties.
Scully:Right. Actually, I knew Haroche before I knew Walther. Haroche was a good friend. We used to stay at each other’s house and exchanged children. Serge and Claudine are old friends. But there is a lot of competition between the German and French groups. And in some sense it probably had nationalistic overtones. I remember some of my French colleagues, indicating that they felt uncomfortable with some aspects of German tradition. I was not so warmly welcomed in Paris after I took the job in Munich. As the years went by, this softened somewhat. But both Herbert and Serge were such excellent experimentalists and such good physicists, that even though there was a strong competition between them, science was improved. Science won.
Bromberg:As you came to Garching, the micromaser was in its earliest stages, wasn’t it?
Scully:It wasn’t even around. It came into being in the mid-eighties.
Bromberg:Were you at all influential in the way it took shape? In 1978 and 1981, you had atoms giving information on the paths of photons. [M.O. Scully and K. Druehi, “Quantum Eraser: A Proposed Photon Correlation Experiment Concerning Observation and ‘Delayed Choice’ in Quantum Mechanics,” Physical Review A 25, #4 (April 1982), 2208-2213]. And with the micromaser, you turn the thing around, and the cavities are giving information on interfering atoms. I just wonder how your ideas, and the experimentalists’, how they were interacting at Garching.
Scully:Well, first of all, the credit for the micromaser goes to Haroche and Walther for their ideas and for actually making the thing. I was involved with Herbert Walther early on in doing theoretical work on the micromaser. The micromaser is really an application of the quantum theory of the laser that Lamb and I developed. That’s really what it is. And so it was natural for me to work with Herbert and others on the way microwaves build up in the micromaser. Then being involved with this device, and having Julian Schwinger visit us in New Mexico one winter, I remarked that I thought that the usual back-action perspective was wrong. The Heisenberg uncertainty resolution was not the protector of quantum mechanics. And Julian said, “Well, there’s always back action. You may find other ingredients in the physics, but the back action at the uncertainty relation type will always wipe out coherence.” So I said, “Well, what if I can find you a case in which there is no back action of the uncertainty relation variety but rather just the presence of knowledge concerning which path (Welcher Weg) wipes out coherence and enforces complementarity wouldn’t that be interesting?” He replied, “Yes, that would be interesting”
So I said, “Ok, the micromaser which path detector can work that way.” And that’s how that idea for a micromaser quantum eraser came about. It was applied to the Wigner problem of splitting beams of atoms, put them through a micromaser, and then put them back together again. If you’ve left which path information in a micromaser on the upper or lower path, then you will always lose the quantum signature, the quantum interference. There is no uncertainty in forcing complementary in this example. It is all about knowledge or potential knowledge. Julian didn’t believe it at first but later he said, “I have changed horses in mid-stream. I now believe it. I will come to you this summer in Munich and we will work on it.” It was a wonderful collaboration.
Bromberg:These were the Humpty- Dumpty papers? [B.-G. Englert, J. Schwinger, and M. O. Scully, “Is Spin Coherence Like Humpty Dumpty? I. Simplified Treatment,” Foundation of Physics 18(1988), 1045. J. Schwinger, M.O. Scully and B.G. Englert, “Is Spin Coherence Like Humpty Dumpty? II. General Theory,” Ziet Phys. D. 10(1988), 135. M.O. Scully, B.G. Englert and J. Schwinger, “Spin Coherence and Humpty Dumpty, III. The Effects of Observation,” Physical Review A 40(1989) 1775.]
This was the essence of the disagreement between Wigner and Lamb. And now using the micromaser idea we saw how to better understand this business of entanglement. There was a series of popular articles — “End to Uncertainty” [New Scientist 6 March 1999, p. 25-28] and “Heisenberg, Take a Hike.” [Science News 154 No. 10, September 5, 1998, p. 149] etc. Have you seen these papers?
Bromberg:No, I haven’t seen these.
Scully:A decade later, in the mid-nineties, people in Germany, Gerhard Rempe, a student of Herbert Walther’s, did experiments which were very much along the line of the Welcher Weg (which path) quantum eraser idea, the idea that duality and the wave-particle nature is somehow protected and enforced, not by nudges or bumps, but just by information, just by quantum correlation... (interruption).
Bromberg:I think we’ve arrived at a natural stopping place, don’t you?
[Interviewer’s Note: The material between curly brackets was not on tape but is transcribed from notes I took on 16 July 2004]
Scully:Our analysis of the lambda transition showed the untenability of neoclassical theory, but it was also a which-way argument, since once can in principle know the state to which the atom transitions. Jaynes countered by proposing that one shine microwaves on the atom and mix the two lower lying states. He thought the microwave field would mix the lower levels and destroy the which path information. But Jaynes was wrong. The mixing is effected by a unitary transformation and can be undone by applying a reverse unitary transformation. By this time, I already had the quantum eraser figured out. So when I saw Jayne’s proposal, I knew what his mistake was. But I chose not to comment on it in print in my 1982 quantum eraser paper. Druehl was a Munich post-doc and a helpful sounding board, and so I put his name down as co-author.
Bromberg:Have you seen Wigner’s 1962 and1963 articles already in the 1960s or only in the 1970s?
Scully:I followed Wigner’s work carefully, so I’m sure I saw them in the 1960s.
Bromberg:Had people been reading the EPR paper in the 1960s?
Lamb had a list of words he prohibited using and EPR was one. It’s not concrete enough, not a detailed analysis. We didn’t read it. Lamb’s prohibition explained why, in our EPR paper, we tracked the particles so carefully. [CD. Cantrell and M.O. Scully, “The EPR Paradox Revisted,” Physics Report 43, No 13, (1978), 499-508].
I met with Julian Schwinger in Munich in the mid- eighties. I already knew him. I told him while on a hiking trip about my position that complementarity did not require a disturbance of the system being measured. He disagreed and thought we needed to calculate the back action of the observer on the system. This is when I suggested that we do an experiment similar to the Scully- Druehl proposal, but with micromasers. That application of the micromaser was mediated by Schwinger.
Englert was Schwinger’s close friend. Englert at first didn’t like it and said “If a student proposed this, he’d be sent out of the room.” We decided to go to Munich and work on it.
[Interviewer’s Note: Transcription of the tape resumes, at Tape 2, midway through side B.]
Scully:All of this has led to new developments on the device-physics side: lasers without inversion, ultra-slow light, quantum computing, and quantum microscopy.
Bromberg:Now how does lasing without inversion, for example, relate to complementarity issues?
Scully: Yes. If you look at my particular kind of lasing without inversion, (lambda versus V fractions), the physics is that of quantum beats. It’s part and parcel of the quantum correlations that we got into and spent time earlier stimulated by Ed Jaynes. It was strictly philosophical. Now here we’re showing that you can make a whole class of lasers based on these ideas. In the first instance we developed the quantum beat laser to reduce the laser line width. We called it the correlated emission laser (CEL). Later we turned the idea around and arrived at Lasing without Inversion (LWI). LWI was something that Steve Harris put me onto. He showed what he was doing to get LWI and I came at it from a different direction. Then I went to Washington and got the money for the experiment, thanks to Hersch Pilloff and to Texas A & M (Ed Fry et al.). And we made the first laser operating without population inversion. It was a big hit. We got a lot of positive feedback.
Bromberg:And this is just a case of turning these ideas over in your mind, and the idea for these applications will occur to you?
Scully:It’s more a matter of an accumulation of tools. We in quantum optics are building more and more tools. The quantum eraser was a very controversial thing when it first came out. We got a lot of hate mail from people saying, “This is crazy.” You mentioned [in the draft paper] Mohrhoff from India. He really hit us hard. But we defended it and you saw his later paper where he said, “I apologize… I was wrong.”
Bromberg:But the more interesting debate may have been with Walls group?
Scully:Yeah, Dan Walls group. That’s right. That debate is the sum and substance of the popular article “Heisenberg, Take a Hike.” It is stated that the people who did the experiment say that this supports the Garching theory. “It appears to confirm predictions made by Englert, Marlan O. Scully, and other theorists.” That was the Walls argument they were talking about. The point is that we don’t hear arguments like that anymore. We see stuff like this “Take a Hike” paper now. [Science News, September 5, 1998].
But now we’re into a new phase. If we use the two- photon state produced by quantum eraser, the resolution of the microscope is substantially improved. And so the perspective of the people who are not supporting basic science is flawed. I wish I could take Mansfield aside and say, “Look at how it works out: If you let us go off and do things like quantum eraser, which is strictly philosophical, it leads frequently to new lasers and new microscopes and new anthrax detectors.” The same physics of coherence in the ground state of a molecule allows us to detect anthrax or make lasers without inversion. If you give scientists a chance, let them have an opportunity to run with their ideas, it will pay off for society, and enhance the richness of our culture of physics and philosophy. It is a win-win situation for both basic science and engineering technology.
Bromberg:Even though we think of the Europeans as more philosophical, I think of you as bringing philosophical issues to Garching. Is that a correct perception?
Scully:I think that’s fair. I think I brought the application of the micromaser to these philosophical which-path ideas of the Max Planck. But they taught us so much. It was really symbiotic. We were teaching each other all the time. I might have nudged them a little more in that direction than they were already going. But once they got the ideas, then, gee whiz, they (progressed in a way) that was just fantastic.
Bromberg: We haven’t talked about the nineties at all.
Scully:Well, the nineties were quantum coherence, lasing without inversion, and ultra-slow light. The application of these ideas now, to quantum thermodynamics and to quantum computing. (Interruption) The realization that quantum eraser, quantum correlations, and correlated spontaneous emission was important really come together from several points of view: From neoclassical/semi-classical theory, and from quantum beats in general. So in 1985, as we discussed earlier, I did what was known as the Correlated Emission Laser (CEL). And that’s a laser that has two excited states coherently populated. And when the atom decay, the photons are correlated, going to a common ground state. And this has noise characteristics which are very favorable.
And then in 1989, stimulated by Steve Harris, I realized that by turning this laser upside down and populating two ground states, with a laser tuned to the mid-point, I could have a laser even though 10% of atoms are upstairs, and 90% are downstairs, no population inversion, so this correlated emission laser led to lasing without inversion. That was a major effort with us, to make such a laser, during the nineties. Around ’95, we made the first such laser. At the same time, we were looking at the index of refraction of media, which are coherently prepared. That is, the CEL has two coherent upper levels, and to our way of looking at it, the laser without inversion has two coherent lower levels, and then we started looking at such phase-coherent media, realizing it’s a new state of matter. We called it phaseonium.
And this leads, for example, to ultra-slow light. And the business of ultra-slow light and lasing without inversion, from my perspective are tied into the early neoclassical problems in which I studied two lower levels. Issues of correlation and coherence come in over and over.
Bromberg:Does Raymond Chiao figure into this part of the story?
Scully:Well, Raymond Chiao did an experiment, which was related to, and a close derivative of the quantum eraser ideas. I was never enchanted with his experiment, because it didn’t have quite what I wanted the experiment to have. I wanted it to like the original ‘82 paper with Druehl [PRA, 25, 2208 ‘82]. Yanhua Shih did such an experiment around ‘99 that I co-authored with him. Raymond Chiao’s experiment was discussed in Newsweek. And Scott Adam, the comic strip creator of “Dilbert”, picked up on it. He talks about quantum eraser, as erasing the past. So here is Newsweek 1995, reporting on quantum eraser. (Picking up the article). But this is just one example. There are many other things took place at Texas A&M around that time e.g. LWI and slow light from hot atoms. Recently, we’ve gone on, using these ideas in quantum thermodynamics and quantum computing, but as I mentioned yesterday, we can make better microscopes (better in the sense that we have higher spatial resolution) by using quantum eraser-Raman pair ideas. Two photons, and each of these are kind of like a Raman emission so you send in this gun light (drawing on board) and then you get a red light out.
Bromberg:I want to ask one general question. There is a lot of told about how science is very different when you go from Cold War to the era of commercialization and globalization. Have you felt any different in the way science has been going on once the Cold War came to an end?
Scully:Absolutely. In the seventies and eighties, I was very much involved with Los Alamos, and Kirtland Air Force Laser Lab etc. I was a member the Physics Division Adversity Council at Los Alamos and spent years working in the defense establishment. But after the Cold War ended, I felt the job was done.
Bromberg:Did you become involved with global companies? Did companies come to you and say, “Boy, we’re interested in quantum computing”? Japanese companies or European companies or American companies?
Scully:Yes, I was always involved with industry and mostly what they were trying to do in those days is to take ideas into new start-up realms. I had a couple of patents and we did indeed have a startup company based on some of these ideas, ideas based on radiation technologies. We worked with those people for a while, but I found it very unsatisfactory because the experience that I had was that they weren’t really interested in technology, they were only interested in making a profit. They weren’t at all interested in science, so I separated from that crew. It’s a long story. I finally ended up becoming a sort of amateur lawyer, and spent time in the writing of legal briefs and filing petitions with the courts. But that’s all, I think, part and parcel of the eighties and nineties, where the sky was the limit. What do they call it…people call it the information technology bubble.
And that’s what it was. It was absolutely a bubble. One time they came to me with a crazy idea that violated the second law of thermodynamics. They asked me if I would look at it for them. They wanted to extract power from fluctuations in the electric grid. I said, “You can’t do that. It violates the second law.” They said, “We want you to look at it anyway, because if it’s true, it’s important…” They wanted to give me $10,000 to evaluate this idea.
Bromberg:That was an easy $10,000.
Scully:Well, yes and no. For free, I could tell them it wouldn’t work. But to see where the guy made a mistake in his design would take me several days. And for that I would take $10,000. So I said: “I want you to sign a letter, which states that I told you it violated the second law, but you weren’t satisfied, you wanted to know where the violation occurred.” So they said, “Oh, if you feel that strongly, we’ll just forget this.”
Bromberg:When the laser came along, and all these people jumped in, like Spectra-Physics, these were people who were interested in technology.
Scully:Sure, those guys were great. They were making things- real devices. Big difference between that and the people in the nineties, those people were selling software and blue-sky. Looking to go public and make money, rather than looking to produce actual lasers or spectrometers.
Bromberg: Whether 9/11 will be a real turning point or not is something I don’t think we know yet.
Scully:That’s for sure. I hope it doesn’t turn out to be as long-term serious as it could. (Interruption). We were doing Kirtland airborne laser lab work in the seventies, long before SDI came into being. We were doing this Star Wars research with Pete Avizonis at Kirkland all through the seventies. And then in the eighties, Reagan and his administration began pushing it very hard. We were still involved — by that time that I had taken joint appointment in Munich and New Mexico — we were still involved, but then everybody jumped on the bandwagon. At some level, the picnic ground was overcrowded. There weren’t really that many problems to go around. And I, if anything, was less actively working with the Air Force at that point.
Bromberg:And they didn’t reach out to Europe and European scientists involved?
Scully:They tried. In some sense, the technology just wasn’t ripe. Lasers were what they were focusing on. They were trying to make higher and higher-powered lasers. We could do that. We knew how to make higher-powered lasers. But we didn’t know how to use the energy to put it on a target 10 or 20 miles away. Atmospheric fluctuations would just scatter the light, and not allow you to focus it. Now, with adaptive optics, those problems have largely been solved.