Quantum unity from packaged cold atoms.

A third group has now succeeded in creating a Bose-Einstein condensate out of a cloud of ultracold atoms. Instead of clumping together while maintaining separate quantum states, as in normal condensation, these atoms end up in a single quantum state and so act as a coherent entity.

Although Albert Einstein and Satyendra Nath Bose independently predicted the existence of this peculiar state of matter more than 70 years ago, no one had observed it until last summer (SN: 7/15/95, p.36; 9/9/95, p.164). In the latest advance, Wolfgang Ketterle and his coworkers at the Massachusetts Institute of Technology have managed to pack and chill more atoms faster than ever before to produce a Bose-Einstein condensate.

"We can get about a million condensed atoms every 10 seconds," Ketterle says. That's enough to start determining the characteristics of this unknown state of matter. These studies may provide insights into other quantum phenomena, such as superconductivity.

The group reports its feat in the Nov. 27 Physical Review Letters.

Ketterle and his coworkers use laser beams to cool and trap sodium atoms. Once the atoms have been brought to sufficiently low temperatures, the team can turn off the light and switch on a weak magnetic field to confine the atoms even more tightly. An extra laser beam serves as a plug to keep atoms from leaking out as they are cooled further.

In one experiment, the group created a Bose-Einstein condensate consisting of as many as 500,000 sodium atoms within 7 seconds at a temperature below 2 microkelvins.

Ketterle and his colleagues are now overhauling their equipment to improve its stability in order to study the sodium condensate. Because no one has yet characterized the material and because the theoretical predictions disagree, these measurements are expected to provide the first clues to the behavior of Bose-Einstein condensates.

"When physicists discover something new, they behave a little like children," Ketterle remarks. "They want to look at it to see what happens. They want to drop it. They want to squeeze, shake, and bang it."

"That's what we're going to do," he says.

For example, the researchers plan to use light to probe the condensate and track its stability. Eventually, the atoms of a Bose-Einstein condensate start combining into molecules, destroying the condensate's unity. "At our high [atomic] densities, we can force this process to happen in a matter of seconds," Ketterle notes.