WSU Physicist First In Northwest To Produce Rare Form Of Matter

By Cherie Winner

Dozens of lenses, mirrors, lasers, and vacuum chambers sprawl across two large tables, linked by electrical cables, optical fibers, and water lines. Physicist Peter Engels flips switches and adjusts dials. The machine clicks through its procedure, and a minute later a computer screen flares with a pencil-shaped bright patch on a field of gray.

"It's the coldest thing in the universe," says Engels, nodding toward the bright image.

He has just produced Bose-Einstein condensate (BEC), a rare and, as Engels calls it, "weird" form of matter in which atoms behave like waves rather than like particles. The ability to produce BEC is something of a holy grail in modern atomic physics; Engels' WSU lab is the first in the Pacific Northwest to accomplish it.

Engels, an assistant professor in the WSU Department of Physics and Astronomy, says being able to make BEC opens up a wide range of experimental possibilities in such areas as nuclear physics, astrophysics, and quantum optics. Comprised of gaseous atoms that are cooled nearly to absolute zero (-459 F), BEC is has potential applications in ultrasensitive sensors of gravitational fields and in powerful new computing systems known as "quantum computers."

Bose-Einstein condensates are even colder than the deep reaches of space, which register about 3 degrees above absolute zero. They were named for physicists Satyendra Nath Bose and Albert Einstein, who in the 1920s theorized that gases would condense into the unusual form if temperatures that low could ever be attained. The feat was accomplished for the first time in 1995 by Eric Cornell and Carl Wieman of the University of Colorado and independently by Wolfgang Ketterle of MIT. These three researchers shared the Nobel Prize for Physics in 2001 for their pioneering work.

Usually, once a technical breakthrough has been made in a scientific field, other researchers are able to repeat the accomplishment more easily. But Bose-Einstein condensate remains notoriously difficult to produce. Engels says the main obstacle is achieving low enough temperatures while retaining enough atoms to form a condensate. Some of the chilling procedures cause atoms to be lost from the sample.

Engels, who worked in Eric Cornell's Nobel Prize-winning lab from 2001 to 2004, drew on his experience there in devising his own system for producing BEC. He and WSU's technical support team designed and built more than 200 parts and purchased nearly 300 more to create his experimental set-up. The project was funded by start-up funds from WSU. It spanned a year and a half and was accomplished with the help of Collin Atherton, a physics major who just completed his sophomore year.

To cool a cloud of rubidium atoms to just a few billionths of a degree above absolute zero, Engels and Atherton combine laser cooling and atom trapping techniques. First, they confine the atoms in an ultrahigh vacuum chamber by using six intersecting laser beams and a magnetic field. This arrangement traps the atoms in the center of the vacuum chamber and cools them to a few millionths of a degree above absolute zero in just a few seconds. The vacuum provides thermal insulation that allows the cloud to reach ultracold temperatures while the instrument as a whole can be housed in the lab at normal room temperature.

A second cooling step removes the fastest-moving (most energetic, highest temperature) atoms from the sample, allowing the remaining atoms to cool further. Eventually they reach a low enough temperature, just a few billionths of a degree above absolute zero, to condense into a BEC. The entire trapping and cooling process takes about a minute. The resulting condensate persists for over a minute, which is more than long enough to perform experiments on how the atoms interact with each other in this highly unusual state.

The BEC develops in the shape of a narrow cylinder. Engels can set his ultra-sensitive camera to capture an image from any one of several vantage points, at any time during the sample's short lifespan, but only one view per experiment. The light used to make each photograph heats the sample enough to destroy it, ending the experiment. Then Engels fires up the machine to prepare another sample.

Engels' device first made BEC on May 4 of this year. Since then, it has produced BEC almost daily. Now that he has a reliable source of the unusual stuff, Engels will proceed with research into its behavior. During his post-doctoral work in Cornell's lab, he showed that when BEC is rotated, the whole mass of it doesn't spin as a drop of water would. Rather, tiny vortices form throughout the BEC. An image of such a sample reveals an arrangement that looks crystalline, with the vortices evenly spaced in a hexagonal pattern.

During the next several months, Engels plans to pursue two areas of inquiry: how BEC responds to shock waves, and the formation of two-component BEC from a mixture of potassium and rubidium atoms.

"He'll kind of explore," says Steven Tomsovic, chairman of the Department of Physics and Astronomy. "It's a new state of matter. So you start playing with it and doing different kinds of experiments, and learning how the physics of that stuff works."

Tomsovic estimates that no more than 30 labs worldwide have the capability to produce BEC. So far, he says, BEC remains a "one lab" endeavor, with all the users of a given machine being members of a single research group. Engels says the technology doesn't lend itself to the multiple-user situation common with particle accelerators and other shared facilities. He and Atherton, having built their device from scratch, know it well enough to keep it running smoothly. Newcomers would need supervision, which he doesn't have time to offer. For the foreseeable future, he'll be far too busy using the machine himself.

Cherie Winner is a writer with the WSU News Service.

Image at top:

Collin Atherton, a junior in the physics department, and Peter Engels (right), assistant professor of physics, with the apparatus they built, the first one in the Pacific Northwest capable of producing Bose-Einstein condensate. Photo: WSU