NIST/University Of Colorado Researchers Create Bose-Einstein 'Super Molecule'
Source: National Institute Of Standards And Technology (NIST)
NIST/University Of Colorado Researchers Create Bose-Einstein 'Super
A super-cold collection of molecules behaving in perfect unison has been
created for the first time from a sea of "fermion" atoms by researchers at
JILA, a joint institute of the Department of Commerce's National Institute
of Standards and Technology (NIST) and the University of Colorado at Boulder
Fermions are a class of particles that are inherently difficult to coax into
a uniform quantum state. The ability to meld fermions into this state---a
soup of particles that acts like one giant, super molecule---may lead to
better understanding of superconductivity, in which electricity flows
through certain metals with no resistance.
The work was described in a paper posted November 7 on the informal physics
archival Web site at [Only registered users see links. ] and will be published online by the
journal Nature on November 26. Researchers Deborah S. Jin of NIST and Markus
Greiner and Cindy A. Regal of CU-Boulder reported that they created a
Bose-Einstein condensate (BEC) of weakly bound molecules starting with a gas
of fermionic potassium atoms cooled to 150 nanoKelvin above absolute zero
(about minus 273 degrees Celsius or minus 459 degrees Fahrenheit).
Jin describes her team's work as the "first molecular condensate" and says
it is closely related to "fermionic superfluidity," a hotly sought after
state in gases that is analogous to superconductivity in metals. "Fermionic
superfluidity is superconductivity in another form," says Jin. Quantum
physicists are in a worldwide race to produce fermionic superfluidity
because gases would be much easier to study than solid superconductors and
such work could lead to more useful superconducting materials.
While fermionic superfluidity was not demonstrated in the current
experiments, the NIST/CU-Boulder authors note that their molecular
condensate was produced by passing through the appropriate conditions for
A separate research group at the University of Innsbruck in Austria reported
on November 13 in the online version of the journal Science that they had
created a similar Bose-Einstein "super molecule" from lithium, fermion
Bose-Einstein condensates are a new form of matter first created by JILA
scientists Eric Cornell of NIST and Carl Wieman of CU-Boulder in 1995 with
rubidium atoms. The pair received the physics Nobel Prize in 2001 for the
achievement. First predicted by Albert Einstein, BECs are an unusual
physical state in which thousands of atoms behave as though they were a
single entity with identical energies and wave forms. Consequently, BECs
have been described as a magnifying glass for quantum physics, the basic
laws that govern the behavior of all matter.
In the world of quantum physics, atomic particles are classified as either
fermions (e.g., electrons, protons and neutrons) or bosons (e.g., photons)
depending on their spin. Fermions have half-integer spins (1/2, 3/2, 5/2,
etc.) and bosons have integer spins (0, 1, 2, 3, etc.). In addition, whereas
no fermion can be in exactly the same state as another fermion, bosons have
no such restrictions. Light waves or photons are the most commonly known
bosons, and laser light is an example of how bosons can behave in unison.
Since 1995, dozens of research groups worldwide have created BECs and
several thousand scientific papers have been published on the subject.
Recently, a number of groups have been working to produce a condensate from
fermions. Superconductivity occurs when electrons (a type of fermion)
combine into pairs. By producing pairing of ultracold fermionic atoms in a
reproducible fashion, researchers hope to explore the physics underlying the
"super" phenomena in unprecedented detail.
In their experiment, the JILA scientists paired up individual fermion atoms
(with half-integer spins) into molecules (with integer spins) and in doing
so formed a Bose-Einstein condensate. The researchers cooled a gas of
potassium atoms (potassium isotope 40) with lasers and confined them in an
optical trap. They then slowly varied the strength of a magnetic field
applied across the trap to increase the attraction between pairs of atoms
and eventually converted most of the fermionic atoms into bosonic molecules.
"Strikingly," they said, the molecular condensate was not formed by further
cooling of the molecules but solely by the increased attractive forces
created with the magnetic field. When the initial temperature of the fermion
atoms was sufficiently low, the gas collapsed into the BEC as soon as the
loosely bound bosonic molecules formed.
Funding for the research was provided by NIST, the National Science
Foundation and the Hertz Foundation.
In October 2003, Jin received a $500,000 John D. and Catherine T. MacArthur
Fellowship, often referred to as a "genius grant."
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