19 July 2001

Form Of Matter Shows Ability To Collapse & Explode

by Kate Melville

A group of Colorado physicists who made worldwide news in 1995 by creating a new form of matter called Bose-Einstein condensate have developed a new "flavor" of the matter that has been delivering surprise after surprise in the laboratory. Composed of scientists from the University of Colorado at Boulder and the National Institute of Standards and Technology in Boulder, the group created the Bose Einstein Condensate, or BEC, in 1995 by cooling atoms of the rubiduim-87 isotope to near absolute zero.

Led by CU-Boulder Distinguished Physics Professor Carl Wieman and NIST Senior Scientist Eric Cornell, the team created a material that shared a quantum state and behaved like a single "superatom."

More recently, using the rubidium-85 isotope, the group has been "tuning" the interactions between the BEC atoms to make them attractive or repulsive by exposing the atoms to magnetic fields, Wieman said. To create the new BEC phenomenon, they cooled the matter to 3 billionths of a degree above absolute zero, now the lowest temperature ever achieved.

A paper on the subject is being published in the July 19 issue of Nature. Authers include Wieman of CU and JILA, Cornell of JILA and NIST, associate researchers Elizabeth Donley and Simon Cornish of CU and JILA, and CU graduate students Neil Claussen and Jacob Roberts.

JILA is a joint institute of CU-Boulder and NIST headquartered on campus. By tinkering with the magnetic fields, the researchers have been able to shrink the condensate, which is followed by a tiny explosion -- similar in some ways to a microscopic supernova explosion and which Wieman's team has dubbed a "Bosenova." About half of the original atoms appear to vanish during the process, he said.

"We have gotten down to the nitty-gritty science and have been able to study the behavior of a new material by manipulating it in new and different ways," Wieman said. The new form of matter created in 1995 is named after Albert Einstein and Indian physicist Satyendra Bose, who predicted its existence in 1924.

"The beauty of the newly created rubidium-85 condensate is that the interactions of the atoms can be experimentally adjusted to be large or small and attractive or repulsive simply by changing the strength of the magnetic field in which the atoms sit," said Wieman.

He said Donley and the team have been able to thoroughly investigate the condensate behavior when the interactions suddenly are changed from being repulsive to strongly attractive. "This is a particularly interesting regime because the physics equations that describe the condensate do not have stable solutions under these conditions," said Wieman.

He likened the situation to the way the equations of gravity cannot be solved under the conditions where the gravitational attraction is so large that a black hole can form. "In this paper, we report the first measurements of what happens to a condensate when the interactions suddenly are made attractive."

The unexpected behavior included parts of the condensate shrinking down into small clumps and a sudden explosion of atoms flying out of the condensate, spewing more energy in one direction than another. Other observations included a fraction of the atoms simply disappearing from sight and a small, quivering condensate left behind as a result of the collapse, he said.

"The extensive set of measurements in this paper provides the first detailed description of the behavior of matter in this very novel physical regime," said Wieman. "This is expected to generate new theoretical ideas that will explain this data and provide a deeper understanding of BEC and quantum physics in general."