|
Implosion
and explosion of a Bose-Einstein condensate "Bosenova"
In a Bose-Einstein
condensate, virtually all the atoms in the ultra-cold gas fall into
the lowest-energy quantum mechanical state. Spread out in space,
they become superimposed on one another, each indistinguishable
from the other, creating what has been called a "superatom."
In quantum-dynamic terms, the same "wave function" describes
them all.
By making a
Bose-Einstein condensate in a particular isotope -- rubidium-85
-- and then changing the magnetic field in which the BEC is sitting,
researchers can adjust the wavefunction's self-interaction between
repulsion and attraction. If the self-interaction is repulsive,
all the parts of the wavefunction push each other away. If it is
attractive, they all pull towards each other, like gravity. Achieving
a pure BEC in rubidium-85 required the cloud of atoms to be cooled
to about 3 billionths of a degree above absolute zero, the lowest
temperature ever achieved.
Making the
self-interaction mildly repulsive causes the condensate to swell
up in a controlled manner, as predicted by theory. However, when
the magnetic field is adjusted to make the interaction attractive,
dramatic and very unexpected effects are observed.
The condensate
first shrinks as expected, but rather than gradually clumping together
in a mass, there is instead a sudden explosion of atoms outward.
This "explosion," which actually corresponds to a tiny
amount of energy by normal standards, continues for a few thousandths
of a second. Left behind is a small cold remnant condensate surrounded
by the expanding gas of the explosion. About half the original atoms
in the condensate seem to have vanished in that they are not seen
in either the remnant or the expanding gas cloud.
Since the phenomenon
looks very much like a tiny supernova, or exploding star, the JILA
team dubbed it a "Bosenova." The most surprising thing
about the Bosenova is that the fundamental physical process behind
the explosion is still a mystery.
Return
to "From Supernova to Smoke Ring: Recent Experiments Underscore
Weirdness of the Bose-Einstein Condensate" News Release
See also: News
from NIST, A-Z Subject Index, NIST
Home Page
Date created:
3/9/2001
Last updated: 5/2/2001
Contact: inquiries@nist.gov
|
