Bose Einstein condensate collapses
In 1924, Albert Einstein and an Indian physicist named Satyendra Bose predicted
the existence of a new form of matter, referred to since then as a
condensate, or BEC, and in 1995, a group of Colorado physicists made
worldwide news by creating this new form of matter. The group, from the
university of Colorado at Boulder and the National Institute of Standards
and Technology in Boulder, created the BEC in 1995 by cooling atoms of the
rubidium-87 isotope to near absolute zero.
Now they have developed a new 'flavor' of the matter that has been delivering
surprise after surprise in the laboratory. Led by CU-Roulder 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,' according to a paper In the July 19 Issue of Nature. The group
has been 'tuning' the interactions between the BEC atoms to make them attractive
or repulsive by exposing the atoms to magnetic fields, according to Wieman.
This time, the group cooled the rubidium-87 isotope to 3 billionths of a
degree above absolute zero, the lowest temperature ever achieved. In an alert
just before the paper was published, Wieman 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.
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, adding ''The beauty of the newly created Rubidium-87
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.''
He also advised that 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, according to 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,
calling these the first measurements of what happens to a condensate when
the interactions are suddenly 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.
''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
Key names: Wieman, Cornell, Elizabeth Donley, Simon Cornish, Neil Claussen
and Jacob Roberts.
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