Researchers Control Love-Hate Relationship Between Atoms

Research that makes ultra-cold atoms extremely attractive to one
another may help test current theories of how all matter behaves – a
breakthrough that might lead to advanced transportation systems, more
efficient energy sources and new tests of astrophysical theories.

The experiment was conducted by a team led by Dr. John Thomas, a
physics professor at Duke University, Durham, N.C., under a grant from
NASA’s Biological and Physical Research Program through the Jet
Propulsion Laboratory, Pasadena, Calif.

The team manipulated a type of interacting atoms that behaved like
fermions — sub-atomic particles that are the building blocks of all
matter, but are difficult to study directly. Normally, these atoms,
called fermionic atoms, avoid each other at all costs. In this case,
the researchers confined and cooled a lithium-6 gas cloud of atoms,
and then introduced a magnetic field that acted as a matchmaker,
inducing the atoms to attract one another strongly.

“This newly-created cold atom system has universal properties,” Thomas
said. “Understanding the behavior of these oddly-interacting atoms
could yield new energy sources by testing the theory of how particles
smaller than atoms behave. The same type of experiment may also help
us study both neutron stars and nuclear matter, which are difficult to
study in nature.” Neutron stars are extremely dense stars made mostly
of uncharged atomic particles.

Thomas and his colleagues used a “bowl” made of laser light in a
vacuum to confine lithium-6 atoms in a cigar-shaped cloud. They
cooled the cloud nearly to absolute zero, the point at which
scientists believe no further cooling can occur and the atoms move as
slowly as permitted by the laws of quantum mechanics. Normally, when
a gas cloud of any shape is released in a vacuum, it expands in all
directions until it becomes a sphere. But when Thomas and his
colleagues introduced a magnetic field, something much different
happened.

“In this case, the lithium atoms played ‘follow-the-leader’ and
expanded rapidly in a direction perpendicular to the cigar shape,
until the gas cloud was shaped like a bulging disc,” Thomas said.
“It’s the first time this type of behavior has been observed in a
fermionic gas and is the result of strong interactions between the
atoms.”

It’s possible the cold atoms used by his team were actually behaving
like a new type of superconductor that could operate at very high
temperatures, Thomas said. A superconductor is a quantum state in
which electricity can flow without resistance. The current generation
of superconductors, used most commonly to make powerful magnets, can
function only at low temperatures.

The ultimate rail system would use cars levitated above the track by
magnets, but because the currently available superconducting magnets
require low temperatures, they are difficult to use. If scientists
could develop a superconducting magnet that could operate efficiently
at high temperatures, it would solve the cooling problem and enable us
to develop advanced high-speed transportation systems.

Thomas pointed out that his team members are not certain they were
observing a superconductor phenomenon in the gas cloud, and further
research is needed to determine whether there could be a different
explanation.

Thomas co-authored a paper on the research, which will appear in the
Dec. 13 issue of the journal Science. The paper appears online at the
Science Express website at
http://www.sciencemag.org/cgi/content/abstract/1079107
http://www.sciencemag.org/cgi/content/abstract/1079107. The
co-authors, all from Duke University include Dr. Ken O’Hara, and
students Staci Hemmer, Michael Gehm and Stephen Granade.

More information on the experiment, including graphics and animation,
is available at
http://www.phy.duke.edu/research/photon/qoptics/news/
http://www.phy.duke.edu/research/photon/qoptics/news/ . Information
on the Biological and Physical Research Program and the Fundamental
Physics Program is available at http://spaceresearch.nasa.gov
http://spaceresearch.nasa.gov/ and http://funphysics.jpl.nasa.gov
http://funphysics.jpl.nasa.gov/.

Thomas’ research was funded by NASA, the National Science Foundation,
the Department of Energy and the Army Reserve Office. JPL manages the
Fundamental Physics in Microgravity Research Program for NASA’s Office
of Biological and Physical Research, Washington, D.C. JPL is a
division of the California Institute of Technology in Pasadena.