Nobelist Carl Wieman talks at CU about super-cold new form of matter

By Briana Collins '03

It's all about a "superatom" that behaves like an individual atom -- only at an incredibly frigid100 billionths of a degree above absolute zero (minus 459.67 degrees Fahrenheit). The temperature needs to be that incredibly frigid to slow the atoms down enough to get them to "fall" into the superatom.

This superatom -- a completely new form of matter -- is called Bose-Einstein Condensate (BEC) after Albert Einstein, who in 1924 predicted that when atoms slow down in extreme cold they lose their 'identities' and coalesce into one single atom. He based his prediction on the work of renowned Indian physicist Satyendra Nath Bose.

Nobelist Carl Wieman lectures in Schwartz Auditorium on Oct. 9. Robert Barker/University Photography

Last year, Carl E. Wieman, a Distinguished Professor at the University of Colorado in Boulder, won the Nobel Prize in physics for his work with BEC. On Oct. 9 Wieman gave the second of his two Bethe Lectures at Cornell in Schwartz Auditorium of Rockefeller Hall, appropriately titled "Bose-Einstein Condensation: Quantum Weirdness at the Lowest Temperature in the Universe."

Wieman, with his co-discoverer of BEC, Eric Cornell of the National Institute of Standards and Technology, led a team of scientists in the late 1980s in experiments to achieve the extremely cold temperature -- the closest to absolute zero ever recorded.

"The Bose-Einstein Condensate really owes its existence to the idea that people studying physics decided it could exist," said Wieman. "Einstein knew that as you got atoms colder, their quantum waves get so big they start to overlap. Then, instead of them having all different speeds, they all decide to fall down to create a single quantum wave -- a superatom."

The team used relatively common, cheap lasers -- like the ones used in CD players -- and magnetic "traps" to create BEC from rubidium atoms. "We were excited because we could do with our $100 lasers what others were doing with $2,000 lasers," noted Wieman. He knew that pushing the atoms with photons -- little "chunks of light" from the lasers -- could exert a larger, collective force on the atoms, which he likened to the force exerted on a bowling ball from large numbers of ping-pong balls being thrown at it. "We set the light so that it would constantly hit [the atoms]," said Wieman. The constant interference from the photons caused the atoms to slow down, almost to a complete stop.

"It's like running in a hail storm," said the physicist. "It hurts no matter where or how fast you run, so you stop."

Ironically, Wieman discovered that the very photons that make it possible for the atoms to slow down are also the photons that prevent the temperature from reaching absolute zero. "Photons are a bit like house guests," observed Wieman, "When they first show up, they're nice to have around. But if they hang around too long they start to get unpleasant." In other words, the photons help slow atoms down, but only to a point -- they still bounce back and forth between the slowed atoms, jostling them a bit and thus preventing them from getting any colder "Luckily," he said, "it turns out it's a lot easier to get rid of light than it is house guests."

In order to prevent further movement of the atoms, the laser light is turned off, allowing the atoms to converge. A current is then run through the field as a magnetic trapping device to hold the atoms in position. The most energetic atoms are removed through evaporative cooling, a process Wieman compares with the steam rising from a cup of coffee. The steam that we see, he explained, "are the most energetic coffee molecules leaping out, taking the hottest part of the coffee with them, so what you have left is cooler coffee." In the same way, the left over, very cold, almost completely immobile atoms are Bose-Einstein Condensation.

Wieman's achievement allows for the exploration of a whole new area of the quantum world. The possibilities for ultra-sensitive detectors of time, gravity and rotation might soon be realized, he said. And, he said, BEC has brought one step closer the creation of gravity-measuring lasers that could predict oil reservoirs -- or even detect if terrorists are hiding in subterranean caves. Indeed, as Wieman professed, "making BEC was really just the beginning, and it's even now, more than ever, allowing us to learn new and interesting things about physics."