The Rochester Review, University of Rochester, Rochester, New York, USA

ost of us dread the middle-of-the-night phone call that jangles us out of bed with news likely to be troublesome. But for a few days each October, scientists everywhere rest only fitfully, half hoping to hear that telephone ring. For those are the days when the Nobel Prize committee metes out awards to the few singled out for the world's top scientific tribute.

But when the call came for Steven Chu '70, he didn't believe it.

The Stanford University professor was awakened at about 3 a.m. last October 15 by a radio station probing his reaction to "winning the Nobel Prize." Chu, who works in a laboratory full of jokesters, figured that he knew the source of the call and declined comment.

But when more calls followed in quick succession, it became clear that this was no hoax: Steven Chu was indeed one of three winners of the 1997 Nobel Prize in Physics.

Most laureates hear the news not from a disk jockey but from the august Nobel committee itself. But area codes around the nation have been changing by the nanosecond, and not even the Nobel panel could keep up with the California changes. Chu finally got official word at 1 o'clock that day--after he'd given a few dozen phone interviews, appeared at a news conference beamed around the world, and, business as usual, had met his graduate-level class in quantum mechanics.

ell, not quite as usual, as it happened. After a standing ovation, the class demanded, and got, a detailed explanation of just how he had used lasers to chill and trap atoms, the basis for his award-winning work.

He had, the class learned, won the prize for demonstrating the truth of a notion that seems implausible, even bizarre--the idea that you could employ lasers, which normally generate intense heat, to create the coldest conditions to be found in the universe. But that is precisely what Chu did.

In the 1970s, at Bell Laboratories in New Jersey, a team led by scientist Art Ashkin had considered the possibility of taming atoms and "locking" them into traps. But progress came slowly and the research had stopped. Then, in 1983, Chu was named head of Bell's quantum electronics department. During conversations with Ashkin, he became intrigued with his ideas and began to consider a number of scenarios that might lead to successful atom-snaring.

Chu was in his office contemplating the subject during a 1984 snowstorm when he began to wonder what would happen if he reversed the approach that most scientists used and got the atoms really cold before proceeding with the trapping. He did some quick calculations and within a couple of hours had worked out on paper a way he could use lasers to both cool and confine them.

Chu, his postdoc, and a technician immediately set about to try the experiment. Thanks in part to his recent success in an effort that management had considered hopelessly difficult (he used a laser to excite positronium, an atom consisting of an electron and a positron, and measured its energy very accurately), Chu's boss "was willing to let me do any hare-brained thing I wanted to, just as long as I didn't lure anybody else into the project," he says.

"We joke that if you have a really great idea, you run into the laboratory and do the experiment," says Chu, an experimentalist. "If the idea's not all that good, you write it up. With this one, we went right to the laboratory.

"We scrounged up a vacuum chamber, and we used some lasers from a previous experiment--the whole thing was pasted together. We spent half a year putzing around the lab putting together the apparatus. By physicists' standards, however, that is very fast."

Receiving the award from Swedish King Carl XVI Gustaf: "I'm still the same person I was yesterday," Chu told reporters. "The moral is that you really shouldn't take these things that seriously." Pause. "I'm thrilled."

When the setup was finally powered up, the team knew within minutes that it had succeeded: They had reduced atoms to the super-cold temperatures where they nearly stand still. (A very slow atom is a very cold atom, since temperature, after all, is just a measure of how fast it is vibrating.)

toms vibrate extremely quickly at room temperature, continually bouncing around minute distances at 2,500 miles per hour, making it nearly impossible for physicists to perform reliable measurements. Chu was able to bring atoms to a virtual standstill, moving at a speed of less than one mile per hour. Think of the comparative speeds of a supersonic jet and a walking ant, he suggests, and you get the idea.

Chu and his team accomplished the task by using light to literally pummel atoms into submission: They sent a stream of sodium gas atoms hurtling into a spot where the beams from several lasers intersected. Then they bombarded the gas from all sides with just the right type and amount of energy to slow down the atoms. To do this, they used photons, better thought of as tiny packets of energy designed to precise specifications, thanks to today's tunable lasers.

If you jolt an atom fast enough in just the right way with photons from enough lasers, Chu showed, you can pin the particle in space, with the photons acting like an airborne straitjacket holding it in mid-air. The straitjacket in this case consisted of photons from six laser beams. With this device, he was able to cool atoms to just millionths of a degree above absolute zero (about -460 Fahrenheit).

Chu called this state "optical molasses," and the name stuck, like--well, molasses. The laser light acts like a thick liquid that slows atoms down, just as real molasses from the kitchen cupboard would slow down a marble moving through it. Some physicists liken the process to using fire hoses to trap a skater on ice: If the firefighters' aim is precise, the skater could be brought to a virtual standstill, suspended among the powerful jets of water.

fter the experiment was shown to be a success, Chu remembers, he ran in to tell his boss's boss during a conference at Bell Labs. "I met him in a hallway and said, 'Guess what? We've managed to trap atoms.'

"He replied, 'Great. What can you do with trapped atoms?'

"I said, 'I don't know, but isn't it great?'"

As indeed it was.

From that success flowed applications no one had envisioned. Now, every day, dozens of scientists routinely cool atoms to near absolute zero. A few have even created a new and exotic state of matter known as a Bose-Einstein condensate, where many atoms overlap and behave like a single giant atom.

The work has also led to the world's most precise atomic clocks (including one built by Chu's group at Stanford). Meticulous time-keeping is key to the operation of computer networks, phone and data lines, radar, and navigation systems such as the Global Positioning System--and, as well, nearly all physics experiments.

Rochester's Nobelists Steven Chu '70, co-winner of the 1997 Nobel Prize in physics, joins a distinguished list of previous laureates with Rochester affiliations: As alumni, physiologist Vincent du Vigneaud '27M (PhD); medical researchers Arthur Kornberg '41M (MD) and Carleton Gajdusek '42; and as faculty members, George Hoyt Whipple, founding dean of the medical school; biochemist Henrik Dam, at the medical school in the 1940s; and economist Robert Fogel, who had been on the economics faculty during the '60s and '70s. Chu, who earned both a B.A. in mathematics and a B.S. in physics, will be back on campus in May--to receive a third Rochester degree, an honorary Doctor of Science to be presented at Commencement.

Chu's team also used laser cooling to create the world's most effective measure of the acceleration of gravity, a method now used by oil companies to test new areas for exploration.

And the research led him to develop "optical tweezers," a laser beam that acts like a tractor beam, enabling it to grip objects. He is using that technology to study individual bio-molecules like DNA.

"Many times in science, you don't know the importance of what you have proposed, or even of what you have done," Chu says. "That was very true with laser cooling. I didn't really appreciate how far-flung the applications would be."

Neither did anyone else when the first scientists conceived the notion of using lasers to cool atoms about 10 years before Chu succeeded in doing so. The idea didn't exactly create a firestorm of interest then, and Chu himself was unaware of the proposal until after he had accomplished the feat experimentally.

uch unexpected twists and turns of the scientific process come as no surprise to Steven Chu, whose father holds a Ph.D. in chemical engineering and whose great uncle, like Steven, is a physicist. That influence, along with a "truly inspirational" physics teacher he had in high school on Long Island, helped put Chu on the lookout for physics when he arrived at Rochester in the fall of 1966. (The University may have been taking a bit of a chance on him. Both Yale and Princeton, he says, had passed on his application, which featured what he calls "ho-hum grades" from high school, though he did finish in the top 10 percent of his class there.)

At the University, a string of good math teachers piqued his interest and he started moving toward a career in that direction. He branched out to earn a double degree, a B.A. in math along with a B.S. in physics. But by his senior year, physics had wholly won back his heart.

"Mathematics is an abstract world created out of pure intellect, while in physics you try to learn about nature," he explains. "In physics, you come up with a theory, and then you can go into the lab and test it."

Professor Thomas Ferbel, who remembers Chu as "a fine lad and a great student," recalls how the budding scientist liked to hang around the department, talking physics. "You had to kick him out periodically," Ferbel recalls.

s a senior, Chu won the Stoddard Prize awarded to a graduating physics major for the most outstanding term paper; he had previously won a similar prize in math. And his grades picked up from high school--he finished Number 3 in his class of 733.

He did squeeze in other activities. He played the trombone in the concert band and also took music lessons at the Eastman School, and he played intramural softball, handball, and tennis. (Though he hasn't kept up with his music, he still takes part in sports daily, playing tennis, swimming, and bicycling up and down the hills around Stanford.) He also was part of a small group of buddies who enjoyed frequent Thursday night trips to the Bungalow, a beer and pizza joint on Mt. Hope Avenue fondly remembered by many other alumni.

"I look back, and in a crazy way, even though the weather was horrible, my years in Rochester were good years. They were among my most carefree."

In 1970 Chu headed for the graduate physics program at Berkeley. "I arrived there expecting to be blown away by people from Harvard, Cal Tech, and MIT, but that didn't happen. Fellow students would come to me to ask for help on the homework, and I began to realize what a terrific education I had received at Rochester."

He stayed on at Berkeley as a postdoc for two years after earning his Ph.D. in 1976, then moved to Bell Labs for a 10-year stint before joining the Stanford faculty. The Theodore and Frances Geballe Professor of Physics and Applied Physics at Stanford, he is holder of numerous other honors, now capped of course by the Nobel.

inning that laurel was not, he admits, a total surprise. His name had been on the list of possible winners for several years, but, as he told PBS's Jim Lehrer, "I always tried to ignore the agitation from my colleagues and just get on with my life."

Now, he's going to have to get on a little differently.

"I've been warned that life will never be completely normal again," he says.

"As a Nobel Prize winner, you become a public figure for all of science. There are some people who really love that role, and while I don't think I'm one of them, I accept it because it draws attention to science and helps publicize it in a positive way.

"Over the last half-dozen years, I've been doing an increasing amount of public service work. As I become older, I assume more of the role of a graybeard. It's part of giving back what you got when you were young and carefree."

Photons, Lasers, and the Weirdness of Quantum Mechanics By Tom Rickey Alumnus Steven Chu '70 isn't the University's only link to the 1997 Nobel physics prize. The University's resident expert on "optical molasses," physicist Nicholas Bigelow, collaborates closely with one of the other winners: Claude Cohen-Tannoudji of the Collège de France and École Normale Supérieure in Paris, who shared the prize for extending Chu's work in cooling atoms to previously unimaginable temperatures. Bigelow spends summers working with Cohen-Tannoudji and is a co-author of one of the key papers the Nobel committee cited in making the award. Bigelow, whose graduate advisor at Cornell won the prize in '96, was working with Cohen-Tannoudji in Paris when the call came announcing this year's winners. Kids, Try This at Home! If you want to see for yourself an event made possible solely by the magic of quantum mechanics, place a golf ball in a box, put the box on a shelf, and walk away. Eventually, someday, the ball will pass right through the box and shelf and fall to the floor. We promise; quantum mechanics says so. Be forewarned, however: The odds of this happening in your lifetime are excruciatingly slim. You'd probably have to wait at least as long as the universe is old (somewhere around 15 billion years) for the telltale thud of ball on floor--or ball on Earth, or ice, or whatever now lies under the shelf. A ball can slip through a box like a beam of light through glass because all matter behaves both as waves and, as we're more accustomed to seeing, particles. Just as the sound waves from your neighbor's lawn mower cut through the strains from your favorite CD, so one form of matter can pass through another under the right circumstances. This occurs frequently with tiny "objects" like electrons that act as waves regularly; in fact, such quantum "tunneling" is now a mainstay of much of today's technology, including microelectronics. But it hardly ever happens with larger objects, such as golf balls and automobiles, which rarely exhibit wave-only behavior. Bigelow is one of about half a dozen professors in the Department of Physics and Astronomy and the Institute of Optics who specialize in the abstruse field known as "quantum optics," in which scientists use photons to manipulate matter and test the theories of quantum mechanics. The University is one of the premier institutions in the world for the study of quantum optics. It should come as no surprise that Rochester would produce a Steven Chu, whose field of laser cooling is intimately related to this study. While Chu was a student, Professors Leonard Mandel and Emil Wolf were organizing the second in a series of seven (so far) Rochester Conferences on Coherence and Quantum Optics, the top gathering in the field. And over at the Institute of Optics during Chu's years at Rochester, faculty and students were helping to invent the tunable dye laser that enables them to deliver precisely tailored packages of energy to atoms--a device that has spurred the field dramatically. Bigelow is the latest addition to the quantum optics team. He joined the University in 1991 and promptly began attracting an impressive array of prizes, including Packard and Sloan fellowships and an NSF National Young Investigator award. The awards are used to pay stipends to graduate students and to buy equipment like super-fast lasers. The ubiquity of "Danger: Laser Operating" signs in campus labs is due in no small part to scientists using the devices to test the dictates of quantum mechanics--the theory that physicists believe rules the cosmos and everything within. Quantum mechanics explains everyday behavior and predicts all sorts of strange things that most people, including a lot of physicists, would rather not think about. The theory holds that everything--an atom, your dog, the Earth--is both a particle and a wave simultaneously. It's a concept that leads down all kinds of crazy avenues. To wit: An object can be in two places at once. Something can be in two seemingly con-trary states (such as alive and dead) at the same time. An event is not real until it has been measured. One event can affect a completely unre-lated event. Time travel and the ability to alter past events may not be an impossibility after all. There are no answers to any questions until the questions have actually been asked. And, the big one: No matter how much you know about the universe, no matter how good your information, you can never, ever be absolutely certain of what will happen next. As bizarre as the predictions of quantum mechanics are, it's a theory that has held up whenever physicists have been clever enough to find a way to test it experimentally. "Quantum mechanics is one of the most disturbing theories you could possibly imagine," says Bigelow. "But it's the most successful theory of nature anyone has yet come up with. The quantum aspects of light provide the best playground for investigating the nature of the universe and for demonstrating the weirdness of quantum mechanics." Mandel has designed and carried out several experiments that other physicists say show most elegantly and simply the truths of the theory, such as the fact that one event can affect another totally unrelated one. He demonstrated this "spooky action at a distance," as Einstein called it, by showing that, if he merely observes one stream of photons, he changes the characteristics of another, completely unrelated, stream elsewhere in his laboratory. In similar straightforward setups involving photons he has shown that there is no reality until someone observes an event and that there are no answers until someone asks a question. For research along these lines, one of Mandel's protégés, Zhe-Yu Ou '90 (PhD), a few years back was named the most outstanding graduate student in the world by the New York Academy of Sciences. Colleague Carlos Stroud at the Institute of Optics says it's no surprise that quantum mechanics seems strange to most people: Even great physicists have had trouble accepting it. With all due respect to Einstein, it seems that God does play dice with the universe. "As long as the strange behavior is hidden at some microscopic level, no one really objects to the theory," says Stroud. "But it's harder to swallow when you start talking about everyday life. Quantum mechanics still seems weird, even to physicists." Like Mandel, Stroud has demonstrated some of the freakish truths of quantum mechanics. Using lasers with ultra-short pulses, he has put an electron into two distinct places at the same time. Then he has used the system to make the electron interfere with itself, a process that lets him look inside an atom more closely than ever before possible. Stroud has also manipulated the energy states of an electron so precisely that a single electron can be used to store information. He has even shown how a single electron can be used as a memory device, storing the words "Institute of Optics." Colleague Ian Walmsley conducts similar experiments, performing the equivalent of a CAT scan on a molecule to study both its wave and particle aspects simultaneously. Much of the theory for tailoring quantum states so precisely, which makes such experiments possible, was laid down by colleague Joseph Eberly, who has written the standard textbook in the field. Such intellectual pyrotechnics by rights, one thinks, should have an equally flamboyant setting. The low-key venue in these River Campus labs, however, gives no hint to the casual visitor that strange truths are here being examined and hidden sights for the first time revealed. Mandel's experiments exhibit simply the flash of lasers and photon detectors silently soaking in the light. Stroud's laboratory features a stream of barely visible sodium gas atoms encountering their fate with powerful laser beams. And in Bigelow's lab, one of the coldest spots on Earth is marked simply by a tiny glowing cloud of gas the size of a grain of rice. For further reading on quantum mechanics, see an article by Ph.D. candidate David Branning in American Scientist, Volume 85, March-April 1997.

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Rochester Review--Volume 60 Number 3--Spring-Summer 1998
Copyright 1998, University of Rochester
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