Oral-History:Arnold Silver
Arnold Silver
Arnold Silver was born in Queens, New York City. He spent his childhood there until moving to the Catskill Mountains at the age of nine. He earned B.S., M.S. and Ph.D. degrees in Physics at Rensselaer Polytechnic Institute (RPI). In 1957, he started work at Ford Motor Scientific Laboratory where he helped develop the Superconducting Quantum Interference Device (SQUID). He has held several positions at Ford until 1969, when he moved first to he Aerospace Corporation, and then to TRW, where he worked as as researcher, research administrator, and Principal or Chief Scientist. Following retirement in 1998, he continued as a consultant for JPL and TRW. Throughout his career, Silver’s research and technical accomplishments have helped create and contribute to the field of superconductor electronics.
In this interview, Silver discusses his research and his achievements in the field of superconductor electronics, devices, and circuits. He outlines his involvement in the development of SQUIDs at Ford Motor and his research work at the Aerospace Corporation and TRW. Reflecting on the challenges and contributions of his career, he describes the evolution of the field of superconductor electronics.
About the Interview
ARNOLD SILVER: An Interview Conducted by Sheldon Hochheiser, IEEE History Center, 14 August 2014.
Interview #659 for the IEEE History Center, The Institute of Electrical and Electronics Engineers Inc.
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Arnold Silver, an oral history conducted in 2014 by Sheldon Hochheiser, IEEE History Center, Piscataway, NJ, USA.
Interview
INTERVIEWEE: Arnold Silver
INTERVIEWER: Sheldon Hochheiser
DATE: 14 August 2014
PLACE: Charlotte, North Carolina
Introduction
Hochheiser:
This is Sheldon Hochheiser of the IEEE History Center. It is the 14th of August 2104. I am here at the Applied Superconductivity Conference in Charlotte, North Carolina with Doctor Arnold Silver. Good afternoon.
Silver:
Good afternoon.
Early Life and Background
Hochheiser:
Okay. If we could begin with a little background. Where were you born and raised?
Silver:
I was born in Queens, New York City. I lived there until I was nine years old. And then we moved up to the Catskill Mountains and I lived there until I went off to college in 1948.
Hochheiser:
What did your parents do?
Silver:
When we lived in New York City, they owned and operated a hand laundry store. And after we moved to the Catskills in a mostly tourist area, they tried various businesses but mostly they operated a summer rooming house, which was then converted to rental apartments. By the time I left for college, they were completely winterized and we were in business year round.
Hochheiser:
Right. Were you interested in science and technical things growing up?
Silver:
Well, it is hard to really know what that means when you are a kid.
Hochheiser:
Yes.
Silver:
But thinking back, I was interested in something technical from a very early age. We had a tenant upstairs in the house we owned and lived in. He was an engineer and I believe he worked for Western Electric. Although when I was a kid, none of that meant anything.
Hochheiser:
Of course.
Silver:
He used to invite me up to his apartment and show me things and one day he was showing me something, which I recollected many years later as a cathode ray tube display of some sine waves and Lissajous figures, etcetera. I think this kind of intrigued me and that’s the thing I always remember back to. This was the 1930’s, before the second world war and television. Radio was the only technology that was pervasive in that era.
Hochheiser:
What led you to Rensselaer for college rather than some other choice?
Silver:
Basically my physics teacher in high school. When I was thinking about going to college, and in those days we didn’t have the internet and information was pretty sparse, particularly in the small town where I went to high school, he told me he went to school at RPI, not that far away, and he thought it was good college and that is how I got directed up there. My parents wanted me to go to a school in New York City where we had many relatives, but that was one place I didn’t want to go. But to show good faith I applied to and was accepted at Columbia University.
Hochheiser:
Now did you go up there planning on studying physics?
Silver:
No. I applied in an engineering department. I think it was electrical engineering but I don’t really remember. You know, the distinction between all these options didn’t make much sense to me in high school. Anyway, I applied to one of the engineering departments and they sent me back a letter and said that class was full but there are spots in Physics and if I wanted to accept I could come, and then I could probably change later. And so I went to Physics and decided there was no reason to change. I much preferred that to the engineering departments.
Hochheiser:
What were the physics curriculum and the other curriculum like at Rensselaer?
Silver:
Well, it was very structured. All freshmen took the same classes. It didn’t matter what your major was: architecture, management, engineering, whatever, you took the same classes: chemistry, calculus, physics, engineering drawing were a must. I think they made everyone take engineering drawing because that way you learned how to spell the name of the Institute. You had to carefully print out the name of the institute on everything you did. There was one humanities class per semester, either an English class or history or economics, whatever. I can’t remember all of them.
Hochheiser:
And what led you to continue on at Rensselaer for graduate work in Physics?
Silver:
I am not sure I really know. I guess in some ways the easiest thing to do was to stay there. I was married and we weren’t very mobile. I knew the school and the area. I thought about other places but in the end I stayed there.
Hochheiser:
What did you concentrate on within the broad fields of physics when you were a graduate student?
Silver:
Well, my interests shifted during those years. I guess initially I thought I would be a theoretical physicist because I didn’t really know very much about hardware and doing experiments. I had never been much of a tinkerer when I was a kid. We didn’t have a lot of stuff to tinker with. I didn’t work on cars and radios and all that stuff. But then after I had been at RPI a short while, I realized that theory was not really what I was cut out to do even though I liked math. I was pretty good at math but it didn’t really interest me that much. This was shortly after the second world war, so atomic and nuclear physics was a very hot topic and I thought I would go into nuclear physics. And that was my idea when I went to graduate school. But when I was a first year graduate student we had a new professor from Harvard who taught a course in nuclear magnetic resonance.
Hochheiser:
His name?
Silver:
His name was Phillip Bray. It had the word nuclear in the name so I figured it must be relevant. In fact, in the early days of that field they thought the biggest contribution would be to measure some nuclear properties. But it turned out that the field evolved very quickly into ways to study structures and bonding in solid-state physics and chemistry. While there was still that element that contributed to nuclear physics, that was not really the major direction in which the field evolved.
Hochheiser:
So that is the field that you pursued then?
Silver:
Right. That is the field that I pursued and I did my dissertation in nuclear resonance.
Hochheiser:
What was your dissertation?
Silver:
Well, I forget the exact title but it was something like Nuclear Magnetic Dipole and Electric Quadruple Resonance in Boron Compounds.
Hochheiser:
Was this with Professor Bray?
Silver:
Yes.
Early Work at Ford Motors Scientific Laboratory
Hochheiser:
What led you upon finishing your dissertation to Ford Motor rather than some other opportunity?
Silver:
Well, when I was finishing up and considering what I was going to do afterwards, I was most interested in finding a position in industry or possibly in a government lab. I didn’t pursue any academic positions. I was offered an unsolicited post doc position at Stanford working for Felix Bloch, who had won the Nobel Prize in that field. But my wife and I were tired of the graduate school existence and a post-doc position promised not much more in that time period. I went to a number of interviews with corporate labs. I was giving a talk at one of the American Physical Society meetings and Jack Goldman came up to me afterwards and introduced himself. He said he was from the Ford Motor Company Scientific Lab and if I was going to be looking for a job why don’t I give him a call. Which I did. I went out to Dearborn, Michigan for an interview and it was a very attractive opportunity. It was a fairly new lab. Lots of empty space, empty offices and an opportunity to do my own research. I didn’t have to fit into somebody’s mold of what they wanted to do and they said I could do whatever I wanted.
Hochheiser:
Do you know what led Ford to be interested in your expertise?
Silver:
I think it was because I had given a paper on nuclear magnetic resonance in glass and they were interested in the properties of glasses. At that time Ford was a vertically integrated company. They were one of the biggest glass producers in the United States, one of the biggest steel producers, etc. So I think that connection got me an interview. It turned out that one of the staff members was John Neighbours, who had been an Assistant Professor at RPI during my first couple of years there. So he knew me and I think that may have helped me get an offer. Basically it was an opportunity to work as if you were at a university defining your own program. But you didn’t have to teach; it was an industrial environment but we didn’t have to justify what we were doing in terms of the company’s business. Our charter was to do good research and publish peer-reviewed papers and enhance the reputation of the organization.
Hochheiser:
So then you continued to work in the same area as your dissertation?
Silver:
Yes. I did for about 5 or 6 years.
Hochheiser:
And what came out of those five or six years in terms of research?
Silver:
Oh, I am not sure anything spectacular but I am proud of what we did. First I had to build up my lab. We did a lot of work, published quite a few papers. I don’t really remember how many there were. I was the first one there in the field of magnetic resonance, and then a couple of other fellows joined. Terry Cole came from Cal Tech, John Lambe from the Willow Run labs of the University of Michigan, and eventually Toshimoto Kushida from Hiroshima University in Japan. We formed the nucleus of what then became known as the Resonance Lab. We did nuclear and electronic spin resonance. It was a pretty tight group. We enjoyed working with each other.
Hochheiser:
Did you each get your own projects?
Silver:
Right. We created our own problems and sometimes we collaborated on an experiment.
Hochheiser:
But you had each other to talk to.
Silver:
Right. We pretty much worked independently, but we were all in one room and discussed our work, we ate together, and so on.
Hochheiser:
You were colleagues.
Silver:
Right. It was a good environment and I enjoyed it. But you know, after five or six years I was thinking that all the things that I was interested in doing I had done, I would like to characterize it as all the easy things were done. The field had matured quite a bit and it was clear if I was going to continue I would have to start doing things in a somewhat different way. So I was looking for and was open to some new opportunity.
Introduction to Superconductivity
Hochheiser:
So is this around when you first got interested in superconductivity?
Silver:
Yes. That is when I got interested in and began to work in this field.
Hochheiser:
What made this area attractive to you at the time?
Silver:
Well, I mean it started off very peculiarly. One of my colleagues in that lab discovered some anomalous signals.
Hochheiser:
Who is this?
Silver:
His name was John Lambe, also called Jack Lambe. He discovered these anomalous signals and we were talking about it and he said, “what is going on here? Where is it coming from?” He spent some time trying to figure out what it was. I had some free time and I said how about I spend some helping you out. He said that was fine so we worked to try to figure out what was going on and that was how we got into superconductivity.
Hochheiser:
Did you figure out what was going on with the anomalous signals?
Silver:
Yes up to a point. Well, we figured out what was probably happening. At that point we couldn’t definitively say this is it, but it was clear it had something to do with superconductivity and flux quantization, and all the rest of it was a mystery. We couldn’t develop any quantitative solution. And then we became aware of some recent publications and so forth.
Hochheiser:
Were these the publications on the Josephson junction?
Silver:
Right, Josephson’s publication in Physics Letters and John Rowell and Anderson’s Physical Review Letter confirming Josephson junctions. We took those and decided to try an experiment. We would define the experiment rather than stumbling across something. And that is how we proceeded.
Developing SQUIDs
Hochheiser:
So now you are on the path that leads to SQUIDs?
Silver:
Right. Although that acronym was sometime in the future.
Hochheiser:
So how did you get from reading the papers and doing experiments to do SQUIDs?
Silver:
From those papers we knew that for Josephson junctions, the phase dependent effects in the junction would be sensitive to magnetic and electric fields, particularly magnetic fields. John Rowell at Bell Labs had published an experiment in which he showed that the critical current depended on the magnetic field and it looked very much like a single-slit diffraction curve. And the equation derived from Josephson had the sinx over x form. We said well, if you’ve got a single slit diffraction from one junction, we should be able to see two-slit interference from two junctions in parallel. That is the type of response we had observed in our microwave experiments. And that is the basic structure of the DC SQUID. Bob Jaklevic, who was in the Physics department but not in the resonance lab, had the vacuum deposition equipment that was needed. He agreed to try to build this experiment. He really did all the hard work because he built the device and then four of us got together to look at the results and--
Hochheiser:
And who was the fourth?
Silver:
The four were John Lambe, Bob Jaklevic, Jim Mercereau, and myself.
Hochheiser:
And what was Mercereau’s role?
Silver:
Mercerau was the only one of the four who had a prior interest in superconductivity. He had come from Cal Tech not too long before. I don’t really know how long before he had joined the lab because I had never interacted with him, but it hadn’t been very long. He was interested in observing flux quantization and basically extending or verifying parts of Fritz London’s theory. Now flux quantization had already been seen in two simultaneous publications, one in the United States and one in Europe, I think Germany. So we knew that flux quantization was a fact. Anyway Mercerau had been working in this area and he had gone to a conference, I think at Colgate, where he learned about Josephson’s work. So he brought us that information and some insight into superconductivity and that whole field, which was just beginning to blossom. So the four of us worked on this problem and we did the first experiment. Jaklevic built this quantum interference device. I remember vividly one day he called us up right after lunch and said, well, I’ve got this device. It’s in a helium dewar and it looks like things are happening. So we all went down to this room where he had set up his experiment. I don’t think I had ever been in that room before. We looked at the oscilloscope trace, an I-V curve of this device and the trace was varying up and down and we could change it. He had incorporated a coil in the helium dewar so we could vary the magnetic field. We tried to take data on a pad of paper by reading the critical current values from the oscilloscope, but it was hopeless. The device was too sensitive; if you took a desk chair and moved it, you would see oscilloscope pattern just wiggle around. So our first attempt to take data with a pad of paper and a pencil, reading off the oscilloscope was not going anywhere.
Hochheiser:
Because moving the pen on the paper was - -.
Silver:
Was too slow. But as we went from one data point to the next one, the situation changed and you couldn’t reproduce anything. You couldn’t do it fast enough. Even if we didn’t move, if something moved in the adjacent hallway, the values changed. In addition, although we didn’t realize it at that instant, we could never have read the oscilloscope with enough sensitivity to plot the data meaningfully.
Hochheiser:
I see.
Silver:
I believe that my major contribution at that point was figuring out a way that we could automate and record the data.
Hochheiser:
So you can capture the data points quickly enough.
Silver:
Right. Right.
Hochheiser:
And how did you do that?
Silver:
Well, it took me about two hours. I convinced the other three guys that if they gave me two hours, I thought we would be able to record the data. So I went back to my lab and stole some of my equipment, namely a phase sensitive detector and an X-Y recorder and used the phase sensitive detector in a mode normally not used, and it looked like it was going to work. It did work and so we rattled off a bunch of graphs. We were all riding pretty high that afternoon because we had results that we were pretty certain were new and exactly what we were looking for. As the day wore on we decided to go celebrate, but there weren’t really many places to celebrate on a weekday evening in Dearborn, Michigan. Eventually we went out and had a pizza and a bottle of wine. We came back the next day and set to work to write a paper, because if you do it in your lab and you don’t tell anybody, it hasn’t happened. So we were in a hurry to publish because we were concerned that [John] Rowell at Bell Labs was on the same track.
Hochheiser:
Just for the record, what is it that you were able to demonstrate?
Silver:
We were able to demonstrate macroscopic superconducting quantum interference in a superconductor device via the Josephson effect. The acronym SQUID was about a year from being coined.
Hochheiser:
How did the research proceed from there?
Silver:
Well, it turned out that the success of our group of four people depended on Bob Jaklevic’s ability to make the devices. We did three experiments in fairly rapid order. The second experiment was similar to the first one except the device was altered so we could put a very tiny solenoid coil into the film. Making that solenoid was a significant challenge that no one in the labs was willing to undertake. Eventually we farmed it out to a subcontractor. The purpose of this experiment was to introduce magnetic flux into the loop without producing any magnetic field where the material was. This was intended to be a demonstration of the Aharonov–Bohm effect, which had been predicted by these two theorists a number of years before. They claimed that the vector potential, which is related to the magnetic field, was not just an artifact of mathematics but had physical reality. The experiment demonstrated this because the only thing that existed at the positions of the materials, the junctions and the superconducting films, was the vector potential. There was no magnetic field there. And yet we saw the same interference effects very vividly. So we published that result. And that produced yet another interesting story. The paper on the Aharonov–Bohm effect was interesting because we sent it off to the Physical Review Letters and they apparently sent it to Aharonov to referee. At that time he was at a university in New York City; I don’t remember exactly where. Apparently he got this Letter to review and read it and I guess he said to himself, I don’t know anything about these experiments. So he called up Bob Jaklevic, who was the first author, and told him who he was and what he was doing, that he was trying to referee the Letter but didn’t have any context of this experiment. Jaklevic talked to him for a while and Aharonov said he was going to approve it, but he also said it sounds really interesting and he was going to go to Oklahoma in a month or two and we were kind of on the way. Were we? And could he drop by. We said, sure. So he came out for a couple of weeks and we sat around and did all kinds of brainstorming. But nothing came of that except we enjoyed interacting with him. So I thought that was an interesting sidelight on how papers do or don’t get published. We did a third experiment to measure the wavelength of the supercurrent de Broglie wave. Afterwards, I rethought that experiment. I am not sure that was a unique interpretation because there are other ways to interpret that experiment.
Hochheiser:
Yes. That is the sort of story that makes things comes to life.
Silver:
Right.
Hochheiser:
You have the printed piece but it’s things that make it seem more substantial in a sense. So there were three letters published in this original series?
Silver:
There were three letters and then there was a Physical Review paper that tied it all together. On second thought, maybe the de Broglie wavelength paper was presented at that year’s Low Temperature Physics Conference that Bob Jaklevic attended.
Hochheiser:
And it would have been presented at the conference then—
Silver:
Right. That would have been presented at that conference and published in the proceedings.
Hochheiser:
By him and not by you.
Silver:
Bob Jaklevic presented the paper, but the publication in the conference proceedings was attributed to all four authors. Since Bob Jaklevic did all the hard work, he deserved the trip to present the paper. Because if he hadn’t been there and had the ability to fabricate the devices, none of this would have happened.
Hochheiser:
If you can’t build a device you can’t do any experiments.
Silver:
Right.
Hochheiser:
So then after these three papers that led to the Physical Review paper, the work now is getting known outside, since you published.
Silver:
Right.
Hochheiser:
And are you hearing from other people?
Silver:
I didn’t. The only one in that group who was known to the superconductivity community was Jim Mercerau, so he apparently was the one who was contacted. The rest of us were just names that were not known to people in superconductivity. But what was happening was Bob Jaklevic was very good. Making junctions was very difficult. And as we moved from the winter toward the summer it got harder to make junctions. We didn’t have the kind of equipment that is available today. And so it got to be more difficult to make devices. Sometime in the spring my friend Jim Zimmerman came on board. Jim was a cryogenic physicist. I mean he was a physicist but had been working in cryogenics.
Hochheiser:
Right. So he was a low temperature physicist.
Silver:
Right. He was a low temperature physicist and also a very clever guy. I spent a lot of time talking to Jim about what we’d been doing and what we thought we understood. He came up with the idea to try to make junctions by a different method. He had niobium ribbon, wire, and lots of material that he accumulated over the years. So he took two niobium ribbons and crossed them like this and used some epoxy to hold them in place and that worked as an interference device. That basically was five minutes, well, more than five minutes; it takes fifteen minutes for the epoxy to cure. Now we had another device that exhibited most of the same properties. Although the junctions were clearly different. They didn’t exhibit all of the properties that the Josephson tunnel junction exhibited. Nevertheless this set us off on a different direction.
Hochheiser:
What direction was that?
Silver:
Making devices without having the long wait time of vacuum deposition and so forth. And around then the original four-person group began to dissolve.
Hochheiser:
Right. Now Jim Zimmerman has come up with a different device for pursuing the same area of research.
Silver:
Right. He came up with a different way to make “junctions”. We didn’t really know that those were Josephson junctions. Something similar but not exactly the same. And it took a long time for what was really happening to be understood. I remember Jack Lambe saying, this is like black magic and not really science. So he and Bob Jaklevic went off to work on other kinds of tunneling phenomena and made their mark there. Mercerau was commissioned by the lab to go to California and set up a group to capitalize on this in some way. Then Jim and I teamed up and set up a lab to pursue this new device research. Zimmerman began to make bulk devices that were machined out of bulk niobium. Jim went from the initial crossed wires to other structures. We took two flat pieces of niobium and by some means were able to lift a little point in one flat. And by pressing that point against the other flat surface we were able to make point contact junctions that exhibited the effects we needed. But we were looking for some way that we could control the parameters of the contacts/junctions rather than you get what you get, whenever you get it.
Hochheiser:
Right. You need predictability.
Silver:
Right. And so Jim developed a screw point contact, which you could adjust.
Hochheiser:
Would this be a little niobium screw?
Silver:
Right. Niobium screws. The diameter of the screw was determined by some wire that Jim had available. This avoided machining such tiny screws. I remember that the thread pitch was 180 turns per inch, which gave us good control of the contact pressure. We eventually settled on that path; that was what we were going to do. And we made many devices that way. Jim used to send designs to our in-house machine shop to machine niobium devices. The machine shop hated to machine niobium; it is a terrible material to machine.
Hochheiser:
What made it difficult to machine?
Silver:
Well, it just kind of balls up and the only lubricants that were known were toxic. I remember the last time Jim sent them a drawing and we got this SQUID back. It did not work. I mean no matter what we did, it did not work. So we concluded that something was wrong, it must not be niobium. We used Archimedes method to determine the density of the machined material, looked it up in the tables and it was not niobium. It was one of the other similar metals but not superconducting, period. After that the machine shop refused to make any more devices. So we convinced the lab to buy us a small milling machine, which we put in the corner of our lab, put a big hood over it and Jim and his associate engineer made all the devices after that.
Hochheiser:
And so what experiments did you do with these new devices?
Silver:
One of the early experiments we did, that I never heard anybody talk about and I haven’t talked about either, was to measure the London moment. I think Jim Mercerau pointed out that if you rotate a superconductor you should induce a magnetic field, something that is called the London moment. We had a SQUID with about a centimeter hole and we set out to do that experiment. We located a non-magnetic building, which had been built purposely for experiments to measure gyromagnetic ratios. It was actually built by a group from the General Motors Tech Center and located at the University of Michigan in Oakland County. Anyway we got permission to go up there and use it. So we built a setup in which we could rotate the SQUID in liquid helium. I don’t remember what kind of a motor we had but I don’t think it was a variable speed drill that you could get today. This was probably 1964. It was a different world. Anyway, we probably spent about a month hauling equipment and liquid helium and liquid nitrogen up there. Jim had a Ford Econoline van, which was very convenient. We took all our equipment up there and set up the experiment. We could look at the interference pattern on the scope and when we started to rotate the SQUID you could see the interference pattern shift. By the displacement of the interference pattern as a function of the rotation speed, we were able to measure the induced magnetic field and consequently the London moment. It was not a high precision measurement but it was a demonstration that the effect existed and could be observed and measured. And while we were doing these experiments, we further realized the sensitivity of the SQUID. The lab was isolated in a big farmland area with nothing much there. We could sit in the lab and look at the scope and see a truck driving down the road about a mile away; we could easily see a shift in the pattern on our oscilloscope. So we knew we had a very sensitive device.
Hochheiser:
Now you also started looking at RF SQUIDs in addition to DC SQUIDs?
Silver:
Right. One of the problems was that in the original tunnel junctions, the voltages you measured were about 3 millivolts. That was easy to measure. You could see it on the oscilloscope easily. Once we went to the point contact type junctions, the signals were now in the microvolt region, probably less than 10 microvolts. I can’t remember the numbers. But with 1960’s technology, measuring microvolts with precision was not very easy. We had DC amplifiers, which tended to drift. We bought some low frequency transformers, so called DC transformers, which boosted the voltage but they didn’t have much bandwidth, which meant that everything was really slow. I still had access to all my equipment in my magnetic resonance lab. So I suggested that we do the measurements at RF instead of at DC, because at RF we could use tuned LC circuits that functioned as transformers. They were wideband and still gave gains of 100 or more. That should make the signals easily seen. So we started to make measurements using RF equipment. Those devices still had two junctions, so we had to adjust two junctions to try to make their critical currents as equal as possible.
Hochheiser:
Right. You got two screws that you are trying to balance.
Silver:
Yes. We had to adjust two screws. That was a nightmarish kind of thing to do. Because, the more you did it, the screws would get blunted and you would have to take the equipment out of the helium dewar, take it apart, and sharpen the screws again. We discovered one time that the device behaved differently. I can’t remember the exact moment that we decided we had a different device. Eventually we concluded that one screw was tightened down sufficiently that its critical current was so large that it was irrelevant. It was no longer a weak contact. It was just part of the loop. So now we essentially had a one-junction device, which is the RF SQUID. That was much more convenient; we only had one junction to adjust. The characteristics of the RF SQUID that we could easily see on the oscilloscope allowed us to measure all the important properties. We could measure the critical current, not necessarily in terms of microamps or milliamps, but in terms of the fundamental properties that were important, namely, the flux quantum and the inductance of the SQUID ring. So with that approach we did all the rest of our experiments with RF SQUIDs and we developed a complete phenomenological model for how the RF SQUID works. And the RF SQUID was much easier than the DC SQUID because it only had one degree of freedom, namely the critical current at one junction rather than two. If you had two junctions, the equations were much messier. They were non-linear transcendental coupled equations and it was not something that I really wanted to play around with. So we were successful in coming up with a closed form mathematical and graphic model. Finally we did an experiment to verify the model. We took two SQUID s and used one SQUID to measure the other one.
Hochheiser:
And then there were several further developments in terms of things like a microwave oscillator?
Silver:
Right. Other people were trying to make microwave sources out of Josephson junctions. But it was extremely difficult because the impedance of a junction is extremely small. The impedance of free space is about 300 ohms and of microwave equipment is 50 ohms. So there was a huge mismatch.
Hochheiser:
Yes.
Silver:
All these attempts at least up to that point were, I wouldn’t say they were totally unsuccessful, but they did not give great results. We had the idea that we could make an oscillator by using the SQUID, and by using microwave techniques we would be able to couple to it. So we fabricated an X band cavity at about 9 gigahertz. think it was a cylindrical cavity, but I don’t remember. And we put the SQUID inside at a point where it would couple to the microwave magnetic field. And this particular SQUID was another accidental discovery, that if the second junction was actually a very tiny resistance, then the device behaved identically to the RF SQUID for frequencies above a certain value, namely the L over R time constant of the SQUID, but it didn’t have the infinite memory that a true SQUID has. A true SQUID has essentially perfect memory. This SQUID would forget in times that were long compared to the L over R time. But that also allowed us to inject a voltage across the junction in this SQUID, which we called an R-SQUID. The other way to generate a voltage was to ramp the magnetic field, but you could only do that for a very short time since you know you can’t keep building current up indefinitely. We actually did some experiments with triangular current waves, which we ramped up and down to try to see the oscillations. And we had some success. Anyway, we did R-SQUID -cavity experiment and were able to observe the microwave oscillations coupled out of the cavity. As expected, we only saw them when the frequency matched one of the cavity modes because it is hard to build up any energy of the cavity if you are not looking at one of its modes. There were a lot of things that we did, which we stumbled upon accidentally, but we were able to say well, what is this and to figure out how to use it. You know, when you get lemons, you can make lemonade or you can throw the lemons away and say it doesn’t taste that good.
Hochheiser:
I guess the other side of that is you developed SQUIDs for oscillating detectors?
Silver:
Right. That was another experiment we did. You know, I worked with Jim for about 5 years there and he had been a friend of mine for quite a few years and we used to argue about how things really worked. We came from different backgrounds and so I had some ideas about how things worked and he had other ideas. This was good because if we agreed too quickly on everything you can’t do anything new. Right? So I had the idea that these devices were really parametric amplifiers. But it was hard to exhibit that in the normal set of experiments. And so we did some experiments that showed that there were parametric amplifier effects.
Hochheiser:
And throughout this period the Ford company remained supportive of this work?
Silver:
Well, yes. We were doing research that that we could publish and outside people were interested and inviting us to visit and talk about it. That was just the sort of things that the lab management was really interested in.
SQUIDs: Beyond the Labratory
Hochheiser:
At what point did these SQUIDs start to come into use beyond your laboratory?
Silver:
Well, fairly early. There was an idea that this might be of interest to the Navy for anti-submarine warfare. And so I think that was one of the things that they tried to capitalize on. Ford had a subsidiary in Newport Beach, California called Aeronutronics which did government contract work.
Hochheiser:
Right.
Silver:
The Ford scientific lab didn’t do any government contract work. We didn’t accept contracts. We were completely internally funded. I think we had a one-dollar a year contract with the Navy that allowed us to get liquid helium. We bought helium gas and liquefied it ourselves. But helium was controlled. You could not just go out and buy it. We tried to transfer some of that work to Aeronutronics and ultimately Jim transferred out there and spent about a year and a half in 1968 and 1969. The Office of Naval Research funded him. The Navy was interested but it was always a tough slog because you had to have liquid helium. And while liquid helium is not flammable, it is not dangerous aside from getting frozen. There was a great reluctance on the part of Navy admirals to put liquid helium on a ship. That was one of the first areas of potential interest outside the lab. Of course a lot of others came along afterwards. But Ford didn’t really capitalize on any of that. And I think after Jim left and I left the whole thing ended.
Leaving Ford
Hochheiser:
Yes. Anything else about your years at Ford?
Silver:
Well, you know it was a great opportunity for a young guy coming out of graduate school to go off and do what he wanted to do. We were essentially only limited by the equipment that you could get and getting equipment was always hard because there was a limited capital budget. And so that was a little tougher but we did get what we needed and we got things done and it was a great place at that time. You know I went there in 1957 in the post Sputnik era. I thought the Physics department started in 1955. And whether Sputnik influenced Ford particularly, there was a national movement at that time.
Hochheiser:
Right. It influenced just about any place remotely or even not so remotely involved.
Silver:
Right.
Hochheiser:
So then what led to your decision to leave Ford?
Silver:
I think it was when I was considering some magnetic levitation experiments. The management had changed. Jack Goldman who hired me at Ford had left to go to Xerox as a Senior Vice President and I think he was really the driving force behind that labs success. We had new management that wasn’t quite as aggressive in helping people do what they wanted to do, promoting it, and whatever.
Hochheiser:
Was there under this new management more pressure to do things that could be more closely tied to the company’s main business?
Silver:
Well, I didn’t really feel that pressure although there were a couple of things that came up that I got involved in. But I guess the whole atmosphere changed. I had the feeling it was time to go.
Work at The Aerospace Corporation
Hochheiser:
Okay. And so then what led you to The Aerospace Corporation?
Silver:
Well, I had no intention of going to California and working in the aerospace industry. I went to Wayne State University and talked to people in the Physics Department about joining the faculty and it looked like that was doable. It was convenient because I wouldn’t have to move my family.
Hochheiser:
Yes.
Silver:
I would just have to drive a little further to downtown Detroit, which wasn’t so bad. But I got a phone call out of the blue from someone I didn’t know about a company that I had never heard of. It was kind of funny because he called me, told me his name was Bob Becker, and asked me whether I was ever interested in moving to California. And I said, no, I had no interest in moving to California and that wasn’t something that my family was interested in doing because our families were all in the East. People weren’t that mobile in those days.
Hochheiser:
Right.
Silver:
Anyway, he talked to me about what kind of job they had. It would be the director of a lab of about 100 people in broadly based electronics research. We talked for a while and I said, well, I was going out to Ford’s Aeronutronics subsidiary to show them what we were doing with SQUIDs and try to get them interested in development for the government. I said that while I am out there, I could stop for a couple of hours before I come back home. So I did. And things evolved and they offered me the job and I took it.
Hochheiser:
Okay. So now suddenly you are managing a large group of people?
Silver:
Right.
Hochheiser:
Were you managing anybody while you were at Ford?
Silver:
A couple of technicians.
Hochheiser:
Yes. That is what I thought.
Silver:
I mean I was a bench scientist.
Hochheiser:
Right.
Silver:
Right.
Hochheiser:
So now suddenly you were managing a large group in a different industry. That must have been quite a change, and in a different part of the country.
Silver:
Right. Everything was changing. When I told my wife I was thinking about taking this job, she said why are you going to do that? Are you going to be a manager instead of a scientist? And I said, I guess I would rather be making the decisions than have somebody else making them for me. It sounded really good and in the end it was a good opportunity and I accepted the job. But of course things changed out there too. That’s one thing about the world. You can’t figure anything is going to last forever.
Hochheiser:
What were the groups that you managed? What did you do in that position?
Silver:
Well, I think initially I had three departments. One department was involved with lasers and optics. These people were working on advanced laser systems. I don’t think there was any real optics aside from that. There was a solid-state devices department that was mostly doing work on diodes, although there were a couple of people in that department working with point contact superconducting junctions similar to those Jim and I had worked with. Except they were trying to make millimeter wave detectors and mixers. There was one department that was heavily into microwave circuitry, antennas, and propagation effects. And it included some work on radio astronomy. My lab operated a very good 15-foot millimeter wave antenna on the roof of our building that worked at 90 and 140 gigahertz, which at that time was the state of the art. It was a really good, well-designed device. And we had some other things going on when I first got there that I don’t quite remember.
Hochheiser:
Now with this large a group were you now 100 percent an administrator or did you have any time to continue to do research?
Silver:
My job was to manage the labs program and direction. I had an administrative assistant who worried about the numbers, etc. My first problem was to learn what was going on, not only in my lab but also in the company.
Hochheiser:
What did you find out about the company?
Silver:
Well, the company was incorporated in the state of California. It was a non-profit that worked for the Air Force. Its role was to provide system engineering and technical direction for the Air Force space and missile systems. One of their main areas was ballistic missile systems, but they were also involved in other Air Force programs. The labs had a dual role. Part of our charter was to do research; the other part was to provide hands-on technical expertise to the Air Force programs. Some parts of my lab were heavily into supporting programs and other parts were heavily into research that didn’t yet connect with the Air Force programs. My attraction to go there was that they had internal funding to support the research program. Now, after I was there a short time that began to change. It was part of this whole national trend away from independent research towards mission-oriented research that was more tightly tied to the company’s products. When I first went there I was trying to set a new course for my labs research and create the organizational structure to further that objective while simultaneously supporting the Air Force’s programs that the company was involved with.
Hochheiser:
Right.
Silver:
They hired me because they wanted to change the labs research directions. So first I had to figure out what was happening in my lab and how to restructure it. I tried to figure out how to do that with the people I had on hand and which people we should try to move out. In the beginning there was a hiring freeze because the Air Force had lost some big programs; the manned orbiting lab called MOL had been cancelled and that cost the company several hundred people via lay-offs, including people in the labs because we were not immune. At some point it became clear that, if we were going to continue to do research in these labs, we had to go out and get independent research funding. We weren’t allowed to compete directly, but we really had to find a way to obtain funding. Most of the people that worked for me did not know how to do that and weren’t in a position to compete for funding. So I got pulled back into the field of superconducting devices because I had a reputation and I had ideas that I thought were marketable. I was able to sell some programs and get funding. So that is how I got pulled back in because when I went there I said I was basically done doing research. I am done. I am out of here. I still had to collaborate with Jim Zimmerman to write a chapter for an Academic Press book that we had agreed to do and I figured that was my swan song.
[End tape 1, begin tape 2]
From Management Back to Research
Hochheiser:
Okay, so you were just starting to talk about how the need to get outside funding pulled you back into research.
Silver:
It pulled me back in a forceful way. When I was the lab director, I learned what people were doing and how they were doing it, why they were doing it. I had ideas on how to do things better, do things they weren’t doing, which I wasn’t bashful about telling them. Why don’t you try this or let’s try to do that. I think I was making an impact on the program because a major part of my job was to define the research program. This was more important than dealing with individuals; I didn’t really deal with many individual people from a management point of view; I had department heads whose job it was to take care of personnel. I had to deal with my department heads and convince them what we should be doing or whatever it was.
Hochheiser:
So did that lead you back to more work on SQUIDs?
Silver:
Well, not so much SQUIDs as such, but we got involved in what I refer to as circuitry, toward devices like analog to digital converters that we wouldn’t think of being SQUIDs but using this technology in a way that we hadn’t done when I was at Ford. Ford didn’t have any microwave or millimeter wave research, or fabrication facilities beyond Bob Jaklevic’s rather rudimentary capability. There were a couple of people working on microwave radar for automobile collision detection. I’m not quite sure how to characterize that because I wasn’t really involved, but I know they weren’t really doing microwave research. But the group I inherited at Aerospace was doing both device and system research at 60 and 90 gigahertz, which are basically millimeter waves. We had antennas and we were studying atmospheric propagation, etc. It was a different mind set. The solid-state group had people who were working on semiconductors, which nobody at Ford was working on. We had some very primitive fabrication capability. So I could think about doing things and talk to people who knew how to do a few things which didn’t exist at Ford. So it is pretty hard to escape from your environment.
Semiconductor/Superconductor Junctions
Hochheiser:
So did this lead to work in semiconductor/superconductor junctions?
Silver:
Yes. That was one of the earliest things. I can’t remember the exact timing. One engineer in my lab was Mike Mullea. He had a Ph.D. from the University of Illinois and was working on semiconductor devices, mostly Schottky diodes. They were trying to make improved Schottky diodes for millimeter wave detectors. I understood what they were doing and one day I said to Mike, why don’t we electroplate some lead on the semiconductor surface instead of whatever material they were using. Because lead is a superconductor, when you go through a Schottky barrier into a superconductor, one should see the quasiparticle energy gap characteristics, which should be more non-linear than the normal Schottky diode. They had to immerse it in liquid helium to make the lead superconducting, which was something they didn’t normally do. Anyway, they did and saw roughly what I expected. We named it the Super-Schottky diode and carried out a sequence of experiments to characterize its properties as a millimeter-wave detector and mixer. It was further interesting because Mike didn’t think he really understood how this worked. I had a young physicist, John Tucker, who worked for me. So Mike went to John and said that Arnold asked me to do this experiment. We did and we saw this result, but I don’t really understand what is happening. Tucker was a theorist and as theorists frequently do, he started from fundamentals and developed the quantum mechanical theory of this device. Tucker came to me one day and said, I worked this up and I have a mistake and I don’t know where it is. I am predicting gain from a resistive device and I don’t see where it is coming from. I said, yes, it seems like you are right. I have no idea why you are seeing gain. He eventually gave up trying to find his error and went to visit Paul Richards at Berkeley, who was making SIS millimeter-wave mixers using Josephson tunnel junctions but not using the Josephson effect. They were hard to make in those days because of the same reason we gave up on tunnel junctions at Ford. Anyway, he went up there, spent some time with Richards and out of that interaction Richards decided to do an experiment to see if this gain was real in our super-Schottky device. They did and it was real. And that led to what became known as the Tucker theory of tunnel diodes. That was a contribution that we hadn’t planned on making and it came about from the sidelight here because one guy didn’t really understand what it was and was looking for somebody to explain it to him in a way that obviously I couldn’t. John Tucker eventually left and I think he ended up at the University of Illinois. But that helped him. Gave him something named after him and that always helps your career. Right?
Parametric Amplifier SQUIDs
Hochheiser:
Absolutely. Now did your work on SQUIDs as parametric amplifiers begin when you were still at Aerospace?
Silver:
It started at Aerospace. Actually the idea that the SQUID was a parametric amplifier started at Ford.
Hochheiser:
Yes.
Silver:
Right. At Aerospace we basically designed a SQUID amplifier, did a lot of simulations and I wouldn’t call it a theoretical paper but it was computational paper. But we didn’t do the experiments. I forget if we tried to make the device because we had pretty primitive fab capability.
Becoming Principal Scientist at Aerospace
Hochheiser:
In 1980 your title at Aerospace changes to Principal Scientist.
Silver:
Yes.
Hochheiser:
Was that a different job or a different title?
Silver:
It was a different job.
Hochheiser:
What was that now?
Silver:
I stepped down from being the director of the lab because again, as it happened at Ford, the management changed. The President of the company and the Vice President who ran the research labs changed. They wanted to go in different directions. They wanted to do some things that I thought were kind of, I’m not quite sure what is a polite word to use but-
Hochheiser:
I get your gist.
Silver:
We basically had a strong difference of opinion.
Hochheiser:
Yes.
Silver:
And so I said, well, okay. If this is what you want the lab to do, you probably don’t want me running it. And so they said, you could step aside, keep your Level 4 position as a Principal Scientist, and if you have funding, you can continue to do your research.
Work at TRW
Hochheiser:
Was that part of why you left and moved to TRW?
Silver:
Yes. Well, obviously that wasn’t going to last very long and it didn’t.
Hochheiser:
Yes. What led you to go to TRW in particular?
Silver:
Well, I had been to a couple of places and when I went to TRW, they had a small group of two or three people who were working in the field of superconductive devices. Their interest or rather that of Roger Davidheiser, who was leading it, was in millimeter wave detectors. Anyway, I went down there and I talked to the head of the Group Research Staff. And he was interested and I was interested for several reasons. One was the fact that at Aerospace, we were prohibited from making hardware. And because I wouldn’t have to move my home. In fact it was closer to my house than Aerospace. I took two miles off my commute each way. We worked out a deal where I emphasized that I didn’t want to come in and displace Roger and be a manager. What I wanted to do was be on the senior staff and have the freedom to build a research program. I thought I could get funding. And of course if you can get funding that makes you welcome.
Hochheiser:
Yes. So I gather you were able to get the funding?
Silver:
Right.
Hochheiser:
Where did the funding come from?
Silver:
My initial funding came from the Office of Naval Research, the same people who had been funding me at Aerospace, plus new funding from the Naval Research Lab.
Hochheiser:
So what did you start working on now that you were back to being a working scientist rather than a scientific administrator.
Silver:
I wasn’t a working scientist in that I didn’t work in the lab. I developed ideas into program concepts, wrote proposals, and interacted with both potential customers and my management with respect to requirements for equipment and staff. I started working on some of the same things that were left unfinished at Aerospace. Namely, A to D converters and microwave amplifiers. I think those were the first two. I think eventually I had two contracts out of the Office of Naval Research and one out of the Naval Research Lab.
Hochheiser:
Okay. So now you are working on a variety of superconducting devices.
Silver:
Right.
Hochheiser:
And how did that work go over the next few years.
Silver:
Well, it went pretty damn slow in the beginning because we were trying to build up our capability to fabricate devices. One of the biggest issues always in this field is being able to make what you can conceive of and what you can design. We had some basic tools and put together some capability to fabricate superconductor circuits, which took a lot of time and I had to convince the company to give us more money to do that.
Hochheiser:
Right. Equipment is not cheap.
Silver:
Yes. Not only equipment but also labor to operate it.
Hochheiser:
You had to also get people who could do the fabrication.
Silver:
Right. And we had to support them because the contracts wouldn’t support the development of your fab. Contracts only support making their devices. They will pay your people for the time they are working on their device but not the time they are building infrastructure. It took me several years to convince the company to invest in the infrastructure if we were going to do this R&D. So it started off pretty slow but eventually we got rolling.
Hochheiser:
And once you were able to build this stuff then you were able to see your ideas in practice or not. You could see what works and what doesn’t work.
Silver:
Right. And when you know what doesn’t work you either give up on it or you fix it.
Hochheiser:
What things worked?
Silver:
Well, the amplifier worked. We finally got that built. Some of the parts in the A to D converter worked although that was more difficult because it was a more complex circuit. An amplifier really needed only one junction imbedded in a microwave circuit. But the A to D converter was a multiplicity of junctions and it took quite a few years before we had a fab capable of producing that.
Hochheiser:
And then once you did, did any of these devices go beyond the lab?
Silver:
Not at TRW. One of the problems with this field has always been that you have to cool things. And that is a huge, huge inconvenience if you are not a research scientist. We were trying to build things that the Air Force could put into space. So we had to have coolers that would fly and survive over long periods of time. One of the reasons that I chose A to D converters for early development is that there was a class of infrared sensors of interest to the Air Force and TRW where the IR detector is already cooled near the temperatures required for superconductor circuits. So it was already providing the bulk of the cooling. Probably one of the mistakes, I made was not pushing into the cryocooler work sooner. It was something that I didn’t know how to do and didn’t really interest me. There were people at TRW working on cryogenics but not at this temperature. Their interest was at 20 degrees kelvin and above. We needed to go down below 10 degrees, preferably 4 degrees, but 5 would have been okay. I guess I had the naïve idea that, if you can make the electronic devices, somebody else will make the cooler. But that didn’t happen fast enough
Hochheiser:
So did you eventually have to move into figuring how to make coolers or did that remain an obstacle?
Silver:
Well, it was always an obstacle and my idea was to buy coolers. But eventually the company did get into coolers. And they have a pretty good group now that is making spacecraft cryocoolers. They tell me they are making the cooler for NASA’s James Webb space telescope.
Reaction to the Discovery of High-Temperature Superconductivity
Hochheiser:
What was your reaction to the discovery of HTS in 1986?
Silver:
Well, my first reaction was that I didn’t believe it.
Hochheiser:
You are not the first person to tell me that.
Silver:
Because I had seen before where people had claimed that they discovered things and it turned out not to be true, so that was my first reaction. But Randy Simon who was working for me at that time said he talked to his friend at the Naval Research Lab and he said it was true. I said then we had better learn what is going on and see if we can use it or whatever. So after I had decided it was true, then what to do about it? From the first materials until Paul Chu pushed the transition temperature of YBCO over 77 K, that happened pretty fast.
Hochheiser:
Yes. It did.
Silver:
I got together with Steve Korn who was the division deputy general manager and we decided to put together a program plan, because we didn’t want to look like we were ignorant or that we didn’t know what’s going on. We want to take advantage of this stuff. So we did. There was a lot of interest all the way to the CEO of the company. It was really hectic. It was more than hectic. The big problem I had was not only to get into this new field, but to protect what I was doing, because we had senior managers in the company who said we should get out of all the low temperature R&D we were doing and just put everything into high temperature superconductors. I worked very hard with support from my boss to prevent that from happening. I prevented us from exiting the field of low temperature superconductors. And that was fortunate because eventually the high temperature stuff faded. If we had committed 100 percent to high temperature superconductors, then we would have been out of business.
Hochheiser:
So you were able to make, you were able to prevail and have the company maintain its program in the low temperature areas.
Silver:
Right.
Superconducting Electronics Program
Hochheiser:
Now also around this time you became a manager again?
Silver:
There was a short period there. I guess the Group Research Center had been reorganized and the department for solid state devices included superconductivity and laser diodes and I am not sure what else. But at some point my boss Bill Simmons called me in. He had discussed with me a number of times about taking over that department and I said I did not want to be a department manager. Department manager is the worst job from my point of view. If you are below that you have less to deal with. If you are above that you don’t have to deal with all the people problems. I said I do not want to be a department head, but one day he called me in and said, don’t give me any objections because you are going to do it, so well I got stuck. It didn’t last very long before I was able to get out of that position by hiring somebody to eventually take the job.
Hochheiser:
And then you were able to go back to being a researcher?
Silver:
I wasn’t really a researcher in the sense that I was in a lab doing anything. I was managing the program but not directly managing people.
Hochheiser:
Ah, and what was the program you were directing then?
Silver:
Well, the superconducting electronics program.
Hochheiser:
Okay. When was this?
Silver:
This happened shortly after high temperature superconductors. I hired, Hugo Chan and I eventually got him appointed department manager so I could get out of that job.
Hochheiser:
And now, so now you are managing a program. So he is dealing with the personnel issues and you are doing programmatic stuff.
Silver:
What I was doing was continuing to define the program; working on proposals to get money; and dealing with the customers. I wasn’t in the lab. People didn’t like me to come in the lab because they didn’t like me turning knobs -
Hochheiser:
They were not your knobs. They were their knobs
Silver:
Right, they were their knobs. Not mine.
Hochheiser:
So were these customers largely government?
Silver:
Yes, government customers plus the company. The company was one of my customers because I had to keep getting money out of the company to maintain and expand our infrastructure.
Hochheiser:
So you were dealing with your program with a mixture of internal and external funding but in either case you had to go out and get it.
Silver:
Right. Get it and defend it.
Hochheiser:
What were the particular programmatic elements? What superconducting devices and circuits?
Silver:
Well, we were still working on A to D converters. These were more sophisticated A to D converters. And we were working on building our fab. That took a lot of my time and effort, not working in the fab, but justifying the need for the fab and getting money to support the fab, expanding it in several ways. We built our first fab in our existing building, which means we had to build a clean room and purchase equipment. There was a major reorganization of the company in 1992 and eventually we had to move to another building, build a new fab. But we didn’t have to build a clean room because they had a better clean room already. In companies like TRW there is always motion.
Hochheiser:
Yes.
Silver:
Physical space and so forth.
Hochheiser:
Did any of these devices move beyond the labs and into use?
Silver:
No.
Hochheiser:
No. Not until much later.
Silver:
Not yet. But they still seemed promising enough that the funding continued to be available.
Hochheiser:
Right.
Silver:
At least the eighteen years I was there.
Hochheiser:
Now I guess we are into the 1990s.
Silver:
Yes.
Superconducting Electronics Organization
Hochheiser:
And now your title is Chief Scientist for Superconductivity. Is this the same programmatic stuff you were talking about?
Silver:
Yes. It is just words on an organization chart. Not much changed except to whom I reported.
Hochheiser:
Right. It is hard to tell when you look at this what is semantics and what is really new.
Silver:
Well, from my point of view my role never changed from the day I came until the day I left, but of course a lot of things changed. We actually got up to about fifty people in the organization at one point. In 1992 the company had a major reorganization and the Applied Technology Division I was in disappeared. Then the question was, to what division is my group going? We ended up moving into an electronics division but not before I spent quite a bit of time talking to the division deputy general manager as to how we would come in, who I would be reporting to, etc. I did not want superconductor electronics to be a department in one of the Centers and he didn’t think I could be a separate Center. So he finally said, why don’t we just call you the Superconducting Electronics Organization? Which was an odd name because nothing else had a name like that. But that gave me direct access to the division management. I didn’t have to go through a Center manager. So, I was manager of the Superconducting Electronics Organization that had one department and Hugo Chan was the manager of that department.
Hochheiser:
So again, he is taking care of the thing, the personnel and certain things that you do not want to take care while you were dealing with the more programmatic things and raising funds.
Silver:
Right.
Hochheiser:
How did the organization’s work progress through the 90s?
Silver:
Well, in the late 1980s and early 1990s, we grew quite a bit with the HTS business. But when that began to collapse, we had to shrink and cut back and actually had to lay people off or find places that they could transfer to, which is the most unpleasant part of being a manager.
Hochheiser:
Yes. I know.
Silver:
I wasn’t the manager but still I was there and I had to break the news that we didn’t have enough money. You guys are going to have to find some way to shrink the staff.
Post-Retirement Activities
Hochheiser:
Yes. Then in 1998 you retired.
Silver:
Yes. I retired in 1998.
Hochheiser:
What was the state of your organization at the time you retired?
Silver:
I thought we were in pretty good shape. I did not want to retire when we were in trouble. I didn’t want to desert a sinking ship.
Hochheiser:
Yes.
Silver:
Right.
Hochheiser:
What were the main projects and research areas towards the end of your career?
Silver:
Well, see we still had a big effort in A to D converters. I think we had more than one funding source for that. We had some other stuff going on. We had a major effort improving our fab. And we were moving to become the center of effort in a high-performance supercomputing program. A computer architecture study called HTMT program had been going on for several years and we became a part of that effort. The next phase would be to begin a hardware demonstration of key parts that could be produced with the existing design and fabrication capability by working with some university groups.
Hochheiser:
Using superconducting circuits.
Silver:
Right. The HTMT program had baselined using superconducting processors.
Hochheiser:
Right.
Silver:
But of course there was a question of who was going to do it, how would it be done and so forth. We were trying to position ourselves to be the center for fabrication and testing, producing these circuits, not so much designing them but being the place to make them and then test them. There were two groups at Stony Brook that were involved in the design. I don’t know if it started before or after I left. We hired one of their physicists who was a circuit designer. But we put a lot of effort, a lot of money into advancing our fab capability to begin to meet the early project requirements. I think that was a big part of our effort. After I retired I went to JPL as a consultant to help coordinate the superconductor parts of that HTMT program, most of which was going on back in my old lab.
Consulting for JPL and TRW
Hochheiser:
So JPL was a customer for this, a funder of this project that you were working on at TRW, and once you retire from TRW, you are now serving as a consultant to JPL on the same project.
Silver:
Right. JPL. And Tom Sterling who was the principal investigator for the HTMT program said he wanted me to serve as the manager of this program from the hardware side. I did that for, I don’t know, a year or two years before their funding disappeared. But I oversaw the work at my old lab to build the designated test chip, which I think is still the most complex superconductor chip built in the United States for computing. It was a microprocessor. In today’s world, a pretty primitive one, but in terms of new technology, groundbreaking.
Hochheiser:
Right. And did you also do consulting for TRW and then after its acquisition by Northrup Grumman?
Silver:
Yes. Through TRW, or maybe it was Northrop Grumman by then, I participated in a government study to assess the technology readiness to develop superconducting supercomputers and to define a hardware project. I also worked on some programs that were classified, so I can’t really talk too much about it.
Applied Superconductivity Conferences
Hochheiser:
Well, in that case I am not going to ask you any more about it. To change the subject a little bit. When did you first attend one of these Applied Superconductivity Conferences?
Silver:
Well, I went to the very first one in 1966. It was called the National Superconductivity Information Meeting, held at the Brookhaven National Lab, and sponsored by the Atomic Energy Commission. In retrospect it was a first of what was to become the ASC.
Hochheiser:
Can you describe what that first conference was like or your recollections of it?
Silver:
Well, there were many people whom I had never met. I think there were only one or two people there that I knew or even knew of. We were invited to participate and I gave a paper on Josephson junctions and SQUIDs. I think it was called Josephson Junction Physics or something like that. I forget the exact title. I think I have gone to almost all of the ASC’s since with one or two exceptions. One was probably in 1968. There was a conference in Texas and I was pretty busy. A young fellow Bob Borcherts was working for me and I asked him to go. I don’t think we presented a paper, but we might have. I remember he told me there was a really interesting presentation about maglev suspension systems that had been conceived by Powell and Danby from one of the AEC labs. We talked about it a little bit. I thought that was interesting and we thought about trying to do something in that area. Borcherts put together a little demonstration to show management and other people how you could easily levitate moving things with magnets. We had a new group attached to the lab at Ford called Transportation Science or something like that. I talked to a couple of those guys who had come from the New York Central Railroad or something like that. They thought that was a pretty interesting idea and they arranged a meeting with a government agency on urban mass transit in Washington. I forget what the group was called, somewhere in the Department of Transportation. We made it clear to them that we were not looking for money, but if the government was interested, we might want to collaborate. After I came back I talked to my boss who was a theorist. This was my new boss. He and another physicist in the department did some calculations and we put together ideas for a little program about superconducting maglev suspension for high-speed rail. I remember a meeting with our Vice President for Research, which is one of the things that helped turn me off of staying there. He said he didn’t know why we wanted to look at any of this stuff. In a few years we are going to have big jets that are going to have all weather capability and nobody is going to need trains or anything like that. And I thought it was kind of an odd posture to take for the Vice President of Research in a company that at that time thought it was going to be a transportation company. So that was one thing that told me I should leave.
Evolution of ASC
Hochheiser:
In what ways has the ASC evolved and changed over the many years you have been participating?
Silver:
Well, it has gotten huge.
Hochheiser:
Yes.
Silver:
There are so many parallel sessions; it is hard to figure out which one you should go to.
Hochheiser:
I noticed the program itself was close to 300 pages.
Silver:
Yes. I mean it is a big organization.
Hochheiser:
Yes.
Silver:
In the early days I served on the program committee and the advisory board. Before the ASC was incorporated, from 1966 until somewhere in the 1970s, it ran more informally. In 1980 Los Alamos was the host and the meeting was held in Santa Fe. Two years before when they were elected to host the next meeting, they suggested that we should incorporate for lots of good reasons. So they undertook the task of doing the incorporation. I think maybe at that point it began to change. Well, there was another important change. The early conferences were all held at national labs. They were sponsored, hosted, and held at one of the national labs. And the topics were heavily weighted toward magnets and magnet materials. Electronics and materials for electronics were small components in the early days. When I attended the first conference in Brookhaven, electronics was a novelty.
Hochheiser:
So the sponsor was one or another National Lab.
Silver:
Right.
Hochheiser:
These were government-funded conferences then.
Silver:
I don’t believe they were government funded because you had to pay to go just like now, but they all were attached to a national lab. The lab provided the administrative support required to host the meeting. I believe that administrative costs are paid out of the registration fees now.
Hochheiser:
I see.
Silver:
Brookhaven, Los Alamos, Fermi, well, not Fermi at that time but Argonne and Oak Ridge one year. The Pittsburgh conference in 1978 was the first one that was hosted by an industrial organization. I remember Charlie Laverick railing about how those dirty contractors were going to take over the conference and we are not going to be the same thing. The idea in the early years was you went to the conferences and then you visited the lab. The Pittsburgh conference was hosted by Westinghouse, and was the first conference that was not hosted by a National Lab. And then the conference was incorporated. I had been on the advisory committee for many years and after it was incorporated I didn’t serve on the Board although I was still involved. In 1986 Ed Edelsack from the Office of Naval Research was the conference chairman. He was a friend and sponsor of mine and he asked me to be the technical program chairman, so I did that. I always like to say that when I was program chairman, I organized the technical program that led to high temperature superconductors. [laughter]
Hochheiser:
That must have taken quite a bit of time being a program chair.
Silver:
Yes. It did. Your time comes in spurts.
Hochheiser:
Yes.
'Silver:
You get abstracts showing up and they piled up on my dining room table. I had stacks of abstracts and I would get faxes and phone calls saying that my abstract is delayed but it is coming. It’s in the mail. The deadline passes and you get all these pleas to consider their abstract although it will be a few days late.
Reflections
Hochheiser:
Looking back, how would you characterize your career as a whole? Greatest satisfactions and achievements?
Silver:
First of all I would say I was lucky.Several times I was in the right place at the right time. And I consider that to be luck. I am certainly satisfied with my career looking back. It is probably more than I ever thought I was going to accomplish. But I think the key was that I somehow managed to work with smart people who would tell me that my ideas were stupid and weren’t going to work. But they weren’t always right either.
Hochheiser:
And more broadly how has the field of superconductor electronics and devices and circuits evolved over your many years of involvement?
Silver:
Well, it has evolved tremendously. In the early years it was a couple of physicists trying to make some little thing and test it. Now the field, at least the field that I was interested in, is building big circuits, doing automated testing and producing things in fab facilities that have some reality to them. What I have learned is that to fabricate this kind of stuff, you don’t want to let a bunch of physicists do it. You need to turn it over to people whose business is fabricating. That is a different kind of business. The people who make integrated circuits don’t have to understand anything about how the Josephson junction works or what a superconductor is or whatever. They need to understand process technology and what happens if you have a problem and how to fix it. The fab business, the semiconductor fab business, likely costs billions of dollars to build a fab and the machines they use are millions or tens of millions of dollars apiece. So, as I was saying at my talk last night, it is now possible to go to a commercial semiconductor fab, and build your circuits there.
Hochheiser:
Except you are piggybacking on the enormous size of the semiconductor industry.
Silver:
Right. You piggyback on that. You pay for it of course.
Hochheiser:
Yes.
Silver:
But you will have a lot better success. You are piggybacking on billions and billions of dollars that have been spent developing tools and techniques and strategies. You will need one extra tool that they don’t have and that is the machine to make Josephson tunnel junctions, because they don’t make Josephson tunnel junctions. I have told my sponsors and customers for years, superconductor circuits are much simpler than making semiconductor devices because we don’t have to do diffusions, we don’t have to do implants, we don’t need high temperature furnaces, etc. We don’t do any of those. So it is a simpler process in many, many ways. But you still have to pay attention to all the same process issues they do.
Hochheiser:
Yes. Well, as you can see my cards are now faced down. Is there anything else you would like to add? Anything that I didn’t think to ask you about?
Silver:
Well, I have covered a lot of ground here. I don’t know if my career is anomalous or not but I don’t think I ever had a plan as to how things were going to go. But I think I was agile enough to go with the flow and at least in some cases find a sweet spot to do things. But I never envisioned when I was starting out that I was going to be here at the end. I don’t think most people starting out, have the end state in their picture. Well, some people have a plan, but I never really had a plan. I just went where the opportunities existed at the time. I am basically a pragmatist.
Hochheiser:
Even if you had a plan, that might not be where you ended up.
Silver:
Well, of course not.
Hochheiser:
Yes.
Silver:
If you are going to be dogged about this is my plan and I am going to stick to it regardless of the facts, then may not work well.
Hochheiser:
Regardless of what the opportunities that present themselves to you.
Silver:
Right. And that is not going to work.
Hochheiser:
Yes. Anything else you would like to add?
Silver:
Without being too boastful, I think I helped create and contributed to the field of superconductor electronics. First with the SQUID work at Ford. Then after IBM taught us how to create a digital logic technology with superconductors based on SQUID devices (although they never acknowledged that connection), John Hurrell and I created the first single flux quantum devices based on the transfer of SFQ pulses by damped SQUIDs rather than current from voltage-latched SQUIDs. Although it took Likharev at Moscow State to improve and popularize such devices and systems. These are almost universally the basis of today’s superconductor circuits. I developed the superconducting electronics organization at TRW, which was in reality a small company, albeit inside a large company. So I am proud of these accomplishments. I always tried to be a responsible member of the superconductor community while protecting my company’s intellectual property and competitive position. I think that is about it.
Hochheiser:
In that case, I think we are done. I thank you for your time. I have really enjoyed listening to you and learning about your career and your work.
Silver:
Well, I still enjoy talking about it.
