The Nobel Prize in Physics 2001
Eric A. Cornell, Wolfgang Ketterle, Carl E. Wieman
I was born in Palo Alto, California in 1961. My parents were completing graduate degrees at Stanford. Two years later we moved to Cambridge, Massachusetts, the city I consider to be my hometown. My father was a professor of civil engineering at MIT, and my mother taught high school English. The family, including my younger brother and sister, accompanied my father on sabbatical years to Berkeley, California and Lisbon, Portugal. These were wonderful experiences for me and no doubt they are in part to blame for my lifelong love of travel.
My mother taught me to read when I was still quite young, and at least in my memory I passed the majority of my childhood reading. My head was always bubbling over with facts and it seems to me this had little to do with my paying close attention in school and more to do with my voracious and omnivorous reading habits. Indeed in elementary school I often kept my desktop slightly open and affected an alert-looking pose that still allowed me to peek into the desk where I kept open my latest book, as interesting as it was irrelevant to the academic subject at hand. Every so often my hand slipped surreptitiously into the desk to turn the page. In the intervening three decades I have spent plenty of time lecturing in front of a classroom of my own, and in retrospect I realize I was seldom fooling anyone. Most of my teachers probably found I made less trouble if they let me read.
Some nights, especially in the early summer when the late evening light kept my west-facing bedroom from getting very dark, I had trouble falling asleep at my appointed bedtime. My parents probably felt that reading me a story was a little redundant, but on occasion my father would come in and suggest to me a "problem" to think about. Stewing over these problems was supposed to help me go to sleep. It never did that, but it did get me in the lifelong habit of thinking about technical issues at all sorts of random moments in my daily life, and not only (or even primarily) during scheduled "thinking time." Some of my father's bedtime problems I now recognize as classic physics brainteasers. A man driving a van full of beehives comes to a bridge. The combined weight of the truck, bees, and beehives barely exceeds the safety limit of the bridge. The driver comes up with the idea of banging on the side of the van, so that all the bees swarm out of the hive and fly around in the back of the van. Does the fact that the bees are now all airborne make the truck light enough to safely cross the bridge? Other problems were exercises in mental estimation. If you hold out your thumb, at arms length, you can just about cover the moon with your thumb. The moon is a quarter of a million miles away. How big is it?
The 1970s, the decade of my teenage years, was a transitional period in American youth culture. It was already past the peak of the era when science-minded kids built radios, model airplanes, rockets - things of that sort. But it was certainly well before the heyday of computers and video games. I was partly old-fashioned and partly modern. I certainly remember building model rockets. It was fun to watch the rocket blast into the air, suspenseful to wonder if the parachute would open to bring the rocket safely back. I didn't really enjoy the assembling the model kits very much, and usually I couldn't be bothered to paint the thing, or even to stick on the decals. A more vivid memory for me was designing a model of my own. Besides the store-bought kits, the Estes Model Rocketry company in those days also sold by mail various sizes of cardboard tubing, balsa-wood sheets, nosecones, and gun-powder rocket engines. Estes also published a terrific little booklet full of quantitative design tips. A key issue in rocket design is to make sure that the center of mass is well forward from the fins, lest the rocket be aerodynamically unstable. My father showed me how (after a candidate design was laid out on graph paper) to calculate the center of mass of the assembly based on the masses and distribution of the component parts. I designed an over-sized, under-powered, clunky sort of rocket. I didn't care how high it would go - I wanted it to rise slowly enough that I could watch to see if its orientation wobbled during the flight. On its maiden flight it lifted off the ground with all the ponderousness of a Saturn V, rising steady and true but rolling slightly about its long axis (had I glued the fins on crooked?) as it gained altitude. The engine burn completed, and then the parachute popped and my creation drifted with the wind to land on the roof of a schoolhouse. My parents suggested I go on Monday morning to ask the school's janitor to retrieve my rocket, but this I was too shy to do.
My freshman year of high school I joined the chess and math clubs. The clubs met after school in the computer-instruction classroom, under the loose supervision of a genial polymath with the unlikely name of Mr. Wisdom. Between rounds of speed chess I read enough of a programming manual to teach myself to write programs on the school's DEC mainframe in the language Basic. For several months I was really captivated with this new activity. The exercises in the Basic manual seemed pretty tedious so I invented a few projects for myself, including a program to generate word puzzles for the math club newsletter. After a semester or so, my infatuation with computers burnt out as quickly as it had begun. Not enough substance there to sustain interest, I felt. This episode is probably the basis for my lifelong distaste for "computers for computers' sake" - it's a kids' game, I think. A second legacy of my brief childhood infatuation with computers was a life-long secret preference for programming in Basic, although during my years of apprenticeship in other scientists' labs I was compelled to learn both C and Fortran. When eventually I had the opportunity to establish a lab of my own, one of my first acts as a young principal investigator was to write a program to output a precisely timed sequence of electronic pulses to control the lasers and magnetic fields in what was to become the first successful Bose-Einstein condensation apparatus. Of course, I wrote the program in Basic!
Some of my classes in high school were pretty interesting and I benefited from having several very intelligent and inspiring teachers. Among these were John Samp, a physics teacher, and JoAnn Walther, an English teacher. After the Nobel Prize announcement, I got back in touch with them and was delighted to learn that they are still (as of 2001) teaching at my old high school.
Just before my final year of high school, my brother, sister and I moved with my mother to San Francisco. I spent my last year of high school there, at Lowell High School. Lowell High was a so-called "magnet school," drawing academically inclined students from all over the city. My fellow students there were very smart, but the really novel thing was that they actually seemed to put a lot of effort into their school work. By the end of my first semester there, I began to get into that habit as well. Something else new at Lowell was that it was "cool" to excel at school, at least among the Asian kids with whom I mostly hung out. Without the transitional year at Lowell, my first year as an undergraduate at Stanford would have been a horrible shock.
The truth is that first year at Stanford was a shock anyway, although not for academic reasons. Everyone was beautiful, self-confident, self-satisfied. Later I moved into a student-run, co-op house and felt more at home in that "alternative" residential atmosphere. It was there I met my future wife, Celeste Landry, although our lives took us separate ways for many years and we were not to marry until more than ten years later.
My first job in physics was as a "scanner" at the Stanford Linear Accelerator Center. As a freshman I needed to earn a little money and I was looking for a way to learn about science at the same time. The advertised hourly wage was unusually high for a campus job, which should have been a danger sign. On my first day on the job, a postdoc spent 30 minutes or so showing me how to call up symbolic representations of an endless series of archived detector "events," for display on a graphics terminal. There was a particular kind of rare event I was to look for - I can't remember now exactly what it was - characterized by a certain precise number of photons, of muons, etc. The postdoc explained to me how to distinguish different sorts of particles on the basis of the amounts of energy they deposited in various sorts of detectors, spark chambers, calorimeters, what have you. When I recognized a promising event, I was to flag it by pressing a certain key on the terminal, and, "pop", another event would come up on the screen for my consideration. After my 30-minute training period was up, the educational part of the job (and incidentally the part of the job involving any human interaction) was essentially finished. I could come in whenever I wanted, work as many hours as I wanted. The money was great but towards the end of the third mind-numbing afternoon of staring at the graphics terminal I realized my sanity was at risk. I decided to quit right then and there, and wandered around the data center looking for someone to notify of my decision. There were plenty of people buzzing around the room, but no one looked familiar. It occurred to me that, after the original 30-minute training period, I had never again seen the postdoc who had taught me the tricks of the high-energy physics trade. Finally I just wandered out of the building, never to return. Over the course of my three afternoons I had worked my way through hundreds of stored events, and flagged four of them as promising candidates. Is it possible those four events eventually got my postdoc a nice assistant professor position at the University of Chicago? One can always wonder!
Meanwhile, I was taking freshman physics with Blas Cabrera, then only in his second year as a professor, and eventually I worked up the nerve to approach him after class. Did he have a position in his lab for an undergraduate? He did! I started off building some data acquisition electronics for a scanning magnetometer, sharing a lab bench with a fellow undergraduate, Charlie Marcus. For the remainder of my years at Stanford I worked afternoons and summers for low-temperature physics groups on campus. I really enjoyed this experience, and it was these jobs, more than anything else, that persuaded me to pursue a career in scientific research.
Roughly halfway through my undergraduate years, I began to worry that my future was choosing me, instead of the other way around. Time seemed to be accelerating. Had I really already completed nearly two years of college? I was taking lots of science classes, spending lots more time in physics labs, and was doing well there. In a little more than a year, the most natural thing for me to do would be to apply to physics graduate school. Doubtless I would be admitted, and then - zoom - off I would go into a pre-defined future as a scientific researcher. It seemed somehow too pat, too canned. When was it that I actually got to decide the course of my own future life? Perhaps I would be happier pursuing something a little more explicitly intellectual than physics. Maybe a return to my first love, of books, was in order. I had been studying Mandarin Chinese for a quarter or two. I took a great interest in politics. Couldn't I put together some sort of future with all that in mind? The first thing I needed was to buy a little time to think it over, lest I be out the door with a degree before I knew what had happened. A Stanford program called Volunteers in Asia seemed to offer me that time. So the summer following my second year of college, I went off to the YMCA in Taichung, Taiwan, to teach conversational English. The work was pleasant and not very hard; I had a lot of time to read and to think and to study Chinese. Six months after that, I left Taiwan, first for Hong Kong and then for mainland China, where I spent another three months studying still more Chinese and generally kicking around the country.
Travel provided many interesting experiences, but perhaps the most useful lesson I learned was that I really had no proficiency for learning the thousands of characters of the written Chinese language. It is not that my memory is generally poor. I am very good at remembering the lyrics to popular songs. A single line from a popular song probably represents about as many bits of information as a single Chinese character. If I could have displaced the one set of information with the other, I would have had no problem storing in my brain the 5000 characters necessary for advanced Chinese literacy. As it was, I realized choosing the study of Chinese literature as my life's work was probably a mistake. Conversely, I came to realize that being good at something is hardly a reason to avoid doing it.
I returned to Stanford with much more of a sense of purpose. I continued to take elective courses in such topics as poetry and political science, but I allowed myself to enjoy my physics courses and my work in the labs. My last two years at Stanford I worked for the gyroscope-based general relativity experiment of Francis Everett and co-workers, with my final year's work growing into an honors project. Everett was the titular advisor of my honors thesis, but I worked more closely with John Turneaure, a research professor. The gyroscope relativity experiment needed data on the low-temperature adsorption properties of helium on various technical materials such as OFHC copper, fused quartz and so on. I inherited a recently abandoned apparatus and was told to extend the range of temperatures and go beyond monolayer coverage. I went to see John for advice as needed, but other than that I was left to work alone. No doubt I wasted a lot of time reinventing the wheel, but I loved the sensation of "having my own lab."
For graduate school I returned to Cambridge. In the spring of 1985, shopping around for a graduate school and a research project, I met Dave Pritchard at MIT. He spun me a wonderful yarn: by very precisely measuring the mass difference between the helium-3 and tritium, one can determine the total amount of energy released in the beta decay of tritium. Combine this mass measurement with a determination (no big deal, Dave implied) of the endpoint of the beta-ray spectrum, and one has measured the rest mass of the electron neutrino! There were hints, in those days, that the neutrino might have a rest mass as large as ten eV, a value of cosmological significance. Think of it, Dave said: working with two or three other students on a bench-top experiment, one might just find the missing dark mass and close the universe! It sounded awfully good to me. It still does, as I retell it today.
Thus in the fall of 1985 I joined Dave's single-ion cyclotron resonance experiment. The idea was to trap a single ion in a Penning trap, measure its cyclotron frequency to great accuracy, then swap in a different species of ion and do a comparison measurement. The ratio of cyclotron frequencies should be just the inverse of the ratio of masses. Two graduate students, Robert Weisskoff and Bob Flanagan, and a postdoc, Greg Lafyatis, had the apparatus designed and largely assembled by the time I arrived, but we didn't succeed in trapping and detecting single ions until three years later. The work got to be pretty frustrating and when at last one morning Robert finally acquired the definitive signal from a single ion, he said "That is that." By that afternoon he had begun writing his thesis and he did not return to the ion lab again. A new graduate student Kevin Boyce had recently joined the group and the two of us spent a couple of years learning how to make precision measurements on the single ions.
It is hard to overstate how much I learned from Dave Pritchard over my five years as a graduate student. He was seldom in the lab, but he ate lunch with us students several days a week, and held regular progress meetings as well. Meeting with Dave could be a fairly overwhelming experience. He frequently was in a sort of quizmaster mode, in which he peppered his student with questions. "How big is this effect? You don't know? That's fine, but why don't you estimate it for me then? No, don't offer to go away and think about it - work it out right now, out loud, for the benefit of all of us here." His quiz sessions could be aggravating or even intimidating, but in the end I found them to be great training. Dave liked to show us how widely disparate effects in quantum and classical physics could be understood with the same basic and rather small set of ideas such as resonance, adiabaticity, stationary points, dressed states, entropy and so on. To this day I have ambitions of designing a course called "The Seven Most Useful Ideas in Physics," that would somehow condense and codify the Pritchardian wisdom. Thus it was that when my five years of grad school were over, while I had come nowhere near to finding the Universe's missing mass, I still felt enthused enough about physics research to proceed on to a postdoc.
There are relatively few experiments in atomic physics these days that don't involve the use of a laser. One major shortcoming in my graduate education in preparing me for a career in atomic physics research was that I had not learned any laser techniques. I felt my postdoctoral job had better fill in that lacuna. Looking for a postdoc job, I made the usual rounds, visiting Yale, Stanford, Bell Labs, Gaithersburg, and so on. Laser cooling was in its heyday in 1990, and as I traveled around I saw all the major programs. I was a little daunted by the size and complexity of the experiments, and worried also that maybe all the really interesting experiments had already been done. Finally, I went out to Boulder to give a talk to Dave Wineland's group in NIST labs. Dave Wineland was and is one of the towering figures in ion trapping, so I felt a little foolish, earnestly describing to his group my modest contribution, but I soldiered on through my talk. No job offer was forthcoming, but as luck would have it, in the audience was a former Wineland-group postdoc, Sarah Gilbert. Sarah called her husband, Carl Wieman, who was looking to hire a postdoc, and suggested that he invite me to make the one kilometer trek from NIST labs over to JILA, on the University of Colorado campus, to visit his lab. At this time the main focus of Carl's research was on precision measurements of parity violation in cesium, but my attention was immediately drawn to his smaller, laser cooling experiment. In contrast to the other laser cooling experiments I had seen, which took up the better part of a room, Carl's experiment could have fit on a card table. Using diode lasers instead of Ar+-pumped dye lasers, and using a tiny little vapor cell instead of an atomic beam machine, the whole experiment seemed accessible and compact, even cute. There was just one graduate student working on the project, and this impressed me as well - if a single student could make it work, how hard could it be? (It would be almost a year later before I realized that Chris Monroe was not exactly an average graduate student!) It was clear to me that during a two-year postdoc I could learn how to make a fun little laser-cooling set up like Carl's, and, looking ahead, it also seemed to me that I could duplicate such an experiment as an assistant professor without much trouble. It would be sufficiently easy to constract that that I would have energy, time and money left over to use the cold atoms in turn to study something else; I would not be compelled to catch up with the established major AMO groups that were studying the cooling process itself.
With an offer from Carl in my pocket, I went back to Cambridge to write up my dissertation. While considering the offer, I began to think for the first time of attempting to see Bose-Einstein condensation (BEC). BEC was a natural thing for atomic physics student at MIT to think about: occupying the office next to Dave Pritchard was Dan Kleppner, co-leader (with Tom Greytak) of one of the major groups attempting to see BEC in spin-polarized hydrogen. The idea of BEC was in the air, and I had seen a number of talks on the topic. Just a year earlier the MIT BEC group had dramatically succeeded in implementing evaporative cooling out of a magnetic trap, a clever idea due to Harold Hess. The MIT hydrogen experiment was daunting in its size and complexity, whereas it seemed to me that if one took as one's starting point the relatively tractable vapor-cell, laser-cooling technology that Wieman was using, it wouldn't be so much of a stretch to imagine souping it up into an apparatus capable of evaporatively cooling to BEC. So I decided to head off to Boulder for a couple of years.
After accepting Carl's offer I postponed actually moving to Boulder for three months while my then girlfriend finished her PhD as well. In the meantime I took a very short-term postdoctoral position working with Joel Parks at the Rowland Institute, helping him design and build a Paul trap for ionized atomic clusters.
In October of 1990 I arrived in Boulder. I found working with Carl to be a very congenial experience. Carl and I share very similar tastes in what makes for an interesting physics experiment, and I was happy to assimilate a fraction of his seemingly endless bag of technological ideas. Carl taught me to decide what part of the experimental apparatus really mattered, and then to spare no effort improving that part. Conversely, Carl emphasized that one needs to recognize where "good enough" was indeed good enough, and to waste no time worrying about it. I learned from Carl's student, Chris Monroe, as well. I had always been reluctant to mess with the innards of a store-bought piece of equipment, lest I break something. Chris' ever-fearless attitude was, if that gizmo isn't doing what we need it to do now, how much worse off will we be even if we do break it? As my two-year postdoctoral appointment wound up, Carl, Chris and I had essentially defined what needed to be done to make BEC with the hybridized method of laser cooling followed by magnetic trapping and evaporative cooling.
During those early years in Boulder, I spent a lot of time trying to imagine what a Bose-Einstein condensate would be like, if we could ever make one. Would it be superfluid, like liquid helium? Would it be coherent, like a laser? What do "superfluid" and "coherent" really mean? I understood these words in the context of the experiments the words had been invented to describe, or at least I thought I did, but it seemed to me that to understand how these words applied to a dramatically different physical system, one had to have a much deeper understanding. Superfluidity and lasing were two of my favorite topics in physics, but each was surrounded by a vast thicket of lore and literature. It was hard to step off of the well-worn paths through these thickets, hard for a newcomer to get a fresh look at the underlying phenomena. If one could make a gas-phase condensate, one would have a less brambled system against which to test one's own physical intuition. Meditations along these lines converted me from BEC dabbler to true believer.
It was with some zealotry, then, that I took the "hybrid cooling to BEC" pitch on the road in 1992, in an effort to find a faculty job. Berkeley and MIT did not bite, but I had offers from Haverford College, University of Virginia and JILA/NIST. The environment at JILA for doing AMO research was so strong, I decided to accept their offer and remain, against the advice of several people who pointed out the potential risks of remaining in the shadow of my postdoctoral advisor. As it turned out, over the years Carl was to be extremely fair in the sharing of credit, and I have never regretted my decision to stay at JILA.
The scientific developments from 1990 to 1995 leading to BEC are discussed in the companion article. In the mid-1990s I ran a secondary research project in parallel with my BEC effort. The idea was to extend the techniques of laser cooling into solid-state systems. We never got it to work. In the end, my sunny optimism was trumped by my complete lack of training in solidstate spectroscopy. As it turned out, a group at Los Alamos National Labs has since successfully cooled a solid using a related experimental approach. Also in the mid-90s, Dana Anderson and I began a project to construct waveguides for matter waves. Our first successes were based on hollow glass fibers, but our ongoing collaboration now focuses on guiding atoms with the magnetic fields from lithographically patterned wires. The bulk of my group's research efforts over the last seven years has focused on elucidating the properties of BEC. With every passing year, BEC proves that it still has surprises left for us. Most lately my group has been pursuing studies of quantized vortices in BEC and of spin-waves in ultra-cold atoms. This latter work required us to retreat back above the BEC transition temperature! (Although we are still comfortably within a millionth of a degree of absolute zero.)
I have been very fortunate over the years in the graduate students and postdocs who have come to work in my lab. Their hard work, talent and creativity have made me look good. I have been fortunate also to live in a society that values scientific research, and is willing to support people to do it.
In 1993, Celeste Landry and I rekindled an old romance and we were married in January of 1995, in the Stanford Faculty Club. At the time of our wedding, I had upcoming professional travel to the ICOLS conference in Capri scheduled for June, and we planned to delay our honeymoon until then. Just two weeks before the ICOLS conference, the BEC experiment finally succeeded. In beautiful Capri, with lovely Celeste, I felt on top of the world.
The next year I experienced a still keener pleasure, attending the birth of our daughter, Eliza. Her younger sister, Sophia, arrived in 1998. The four of us live in an old brick house in the shade of two large silver maples in central Boulder.
From Les Prix Nobel. The Nobel Prizes 2001, Editor Tore Frängsmyr, [Nobel Foundation], Stockholm, 2002
This autobiography/biography was written at the time of the award and later published in the book series Les Prix Nobel/Nobel Lectures. The information is sometimes updated with an addendum submitted by the Laureate.
Copyright © The Nobel Foundation 2001
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