Physicist produces rare, ‘weird’ Bose-Einstein matter
(Physicist Peter Engels and student in lab)
PULLMAN — 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,” said 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’ Washington State University lab is the first in the Pacific Northwest to accomplish it.
Engels, an assistant professor in the 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 degrees Fahrenheit), BEC 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 the 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 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 sophisticated 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 – more than long enough to perform experiments on how the atoms interact with each other in this highly unusual state.
Steven Tomsovic, chairman of the Department of Physics and Astronomy, said Engels’ ability to generate BEC “gives us the opportunity to get into the forefront of a whole new area of physics.” He said Engels’ experimental work is complemented by theoretical research on BEC being done by Doerte Blume, also a member of his department.
Undergraduate student Collin Atherton (left) and physicist Peter Engels with the device they built, which is the first in the Pacific Northwest capable of cooling a gas to nearly -459oF and producing the rare form of matter called “Bose-Einstein Condensate.”