![Physicist Deborah Jin in her laboratory at JILA.](https://webarchive.library.unt.edu/eot2008/20080917104654im_/http://www.nist.gov/public_affairs/images/coldmoleculedeborah.jpg)
Physicist Deborah Jin in her laboratory at JILA, a joint institute of the National Institute of Standards and Technology and the University of Colorado, Boulder. © Geoffrey Wheeler |
A team
of researchers at JILA, a joint institute of the Commerce
Department’s National Institute of Standards and Technology
(NIST) and the University of Colorado at Boulder, has done
the physics equivalent of efficiently turning yin into yang.
They paired individual potassium atoms belonging to a class
of particles called fermions into molecules that are part
of a fundamentally different class of particles known as bosons.
Though the transformation lasts only a millisecond, the implications
may be long lasting.
The
work, reported in tomorrow’s (July 3) edition
of the journal Nature,
is an important step toward creating a “super molecule,”
a blend of thousands of molecules acting in unison that would
provide physicists with an excellent tool for studying molecular
quantum mechanics and superconductivity. Creation of a “super
atom” (known as a Bose-Einstein condensate or BEC;
see
www.bec.nist.gov for
more information) earned another research team at JILA the
2001 Nobel Prize in physics.
In the
Nature paper, NIST’s Deborah Jin and colleagues
describe their experiments to produce these exotic molecules
at temperatures of only about 150 nanoKelvin above absolute
zero. The technique involves manipulating a cloud of atoms
within an ultra-high vacuum chamber with lasers and magnetic
fields to coax the atoms to
pair up into loosely joined molecules. Surprisingly, the researchers
report, the number of molecules produced is very large—with
about a quarter million or 50 percent of the atoms within
the original cloud pairing up.
“This
work,” Jin notes, “could help us understand the
basic physics behind superconductivity and especially high-temperature
superconductivity.”
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The
images above show the creation of ultracold molecules
during the JILA experiments. Left -- A rainbow color
scale indicates the numbers of ultracold gaseous potassium
(K40) atoms in the vacuum chamber in two different fermion
states. White areas have the most atoms, blue areas
have the fewest.
Center
--After a carefully tuned magnetic field is scanned
over the chamber, 50 percent of the atoms "disappear."
About half the atoms pair up into loosely bound molecules
and are now bosons with different states not detected
by the experimental set up.
Right--A low-energy radio wave is directed at the chamber. The molecular bonds are broken and the atoms reappear in a third fermion state (fuzzy blue area in center of image).
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Superconductivity
is a property in which electrons (a fermion particle) move
through a metal with no resistance. The experiments may lead
to creation of fermion superfluids made from gases that would
be much easier to study than solid superconductors.
“Our experiments,”
Jin continues, “produced the lowest molecular binding
energy that has been measured spectroscopically.” In
other words, the atom pairs forming each molecule are hanging
on to one another by their proverbial fingertips. They also
are spaced very far apart by molecular standards. The researchers
measured the amount of energy required to hold the molecules
together by breaking the molecular bond with a relatively
low-energy radio wave. Most molecular bonds require higher-energy
light waves to break them apart.
The atoms, a form
of potassium with one extra neutron (the isotope of potassium
with a molecular weight of 40 rather than the more common
39), are classified as fermions. Fermions are the particles
most people are familiar with—i.e., protons, neutrons,
electrons—and they obey one basic rule. No fermion can
be in exactly the same state at exactly the same time and
place as another fermion. Hence, no two things made of ordinary
matter can be in exactly the same place at exactly the same
time.
The molecules formed
from these potassium atoms, however, are bosons. Unlike fermions,
bosons can be in exactly the same energy state in exactly
the same time and space. Light waves or photons are the most
commonly known bosons, and laser light is an example of how
bosons can behave in unison. Bose-Einstein condensates (BECs)
are the atomic equivalent of lasers. First produced in 1995
by JILA scientists Eric Cornell and Carl Wieman, BECs are
a fourth state of matter in which a dense cloud of atoms acts
like one huge super atom.
Funded by NIST
and the National Science Foundation, the current work of Jin
and her colleagues—Cindy A. Regal, Christopher Ticknor
and John Bohn—builds on these earlier experiments.
As a non-regulatory
agency of the U.S. Department of Commerce’s Technology
Administration, NIST develops and promotes measurement, standards
and technology to enhance productivity, facilitate trade and
improve the quality of life.
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Created:
07/02/03
Last updated:
03/15/2004
Contact: inquiries@nist.gov
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