About the Director of Berkeley Lab

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Steven Chu Named Sixth Lab Director

A Scientist's Random Walk
A Conversation with Steven Chu
Institute of International Studies, UC Berkeley, 2004

On Thursday, June 17, 2004, the Regents of the University of California named Steven Chu the new Director of Lawrence Berkeley National Laboratory.

Since 1987, Chu has been a professor of physics at Stanford University. For the previous nine years he was at Bell Laboratories in New Jersey; there he did the research that led to his 1997 Nobel Prize in physics, which he shared with Claude Cohen-Tannoudji and William D. Phillips, for methods to cool and trap atoms with laser light.

Chu received his Ph.D. from the University of California at Berkeley in 1976 and was a post-doctoral fellow there until 1978. He got his B.S. in 1970 from the University of Rochester. He graduated from Garden City High School in Garden City, New York, as a self-described "A-minus student — and by my family's standards, this was appalling."

However he still remembers the gifted high-school physics teacher who encouraged experimentation and "ambitious laboratory experiments," including a pendulum Chu built in order to measure the force of gravity "with precision." Chu's choice of experimental design was influenced by his childhood passion for Erector Sets. "An understanding mother allowed me to keep the projects going for days on end," he says. He notes, ironically, that 25 years after his high school measurement of gravity he did a refined version of the same measurement "using laser-cooled atoms in an atomic fountain interferometer."

Chu's parents came from China to the Boston area just prior to World War II, while his father was finishing his education at MIT; they decided to stay on because of the war. Chu and his brothers were born in different cities while his father followed "a typical nomadic academic career"; Chu was born in St. Louis in 1948 but raised mostly in New York after his father became a professor at the Brooklyn Polytechnic Institute.

On Long Island Chu discovered one of his heroes, Yogi Berra, "the great American philosopher of the twentieth century. One of the things he said is, 'You can see a lot by watching.'" It was in this spirit that many of Chu's scientific successes came to him, including the rare "eureka moment" that led him, while at Bell Labs, to conceive of the laser cooling and trapping of atoms in terms of Einstein's analysis of Brownian motion. In similar fashion, Chu extended his techniques for trapping atoms and other small particles to investigate biological problems such as the folding of proteins and other macromolecules — tools and methods that are now at the forefront of research in the field.

Chu says that "Science is really about describing the way the universe works in one aspect or another in all branches of science — how a life-form works, how this works, how that works. . . . You have to have a natural curiosity for that."

It's a good description of the kind of work that goes on at Berkeley Lab — and of the exhilaration of Chu's new assignment as Lab Director. In accepting the post, Chu was presumably guided by another of his favorite Yogi Berra aphorisms: "If you come to a fork in the road, take it."

“It’s remarkable
what simple curiosity
can lead to.”

— Steven Chu

To Catch an Atom, continued

“Arthur Ashkin at Bell Labs started me thinking about holding onto an atom with light back in 1983,” Chu said in an earlier interview. “The conventional wisdom at that time was first you hold the atom with light and then you make it cold so you can do what you want with it. My idea was to reverse this by cooling the atom first, then grabbing it with light.”

In 1985, Chu and his team at Bell Laboratories in Holmdel, N.J., used six laser beams, opposed in pairs and arranged in three directions at right angles to one another, to create what he called “optical molasses.” While photons in a laser beam have no mass, they do have momentum. If the energy of a moving photon resonates with the energy of a moving atom at the time a collision occurs, the photon will transfer its momentum to the atom, giving it a push in the direction at which the photon was moving.

Working in a vacuum to avoid freezing the atoms into a solid state, Chu and his team hit a beam of sodium atoms with an opposing beam of laser light. This slowed the atoms down and allowed them to be steered into an intersection where the six cooling laser beams met. Atoms caught in the laser crossfire had nowhere to go without being hit by another beam and pushed back to the center of the intersection. A glowing cloud about the size of a pea formed, containing about a million super-chilled sodium atoms.

“Atoms in the optical molasses take what is called a random walk — moving around aimlessly as they’re hit from all sides by photons,” Chu once said. “The trap is a tempting resting place.”

Chu and his team were able to cool the atoms to 240 millionths of a degree above absolute zero. Subsequent work by American physicist William Phillips and French physicist Claude Cohen-Tannoudji, who shared the Nobel Prize with Chu, brought the temperature down to one micro-Kelvin, or one millionth of a degree above absolute zero.

Caught in optical traps at such low temperatures, atoms can be studied in great detail to help us learn more about such things as the interplay between radiation and matter. The traps can also be used to create an atom interferometer for measuring acceleration, gravity and rotations with very high accuracy. The optical molasses technique also led to the discovery of the esoteric form of matter known as a Bose-Einstein condensate.

Said Chu when he won the Nobel Prize, “It’s remarkable what simple curiosity can lead to.”