June 24 -- NASA-funded
researchers at the Massachusetts Institute of Technology, Cambridge, Mass.,
have created a new form of superfluid matter. This research may lead to
improved superconducting materials, useful for energy-efficient electricity
transport and better medical diagnostic tools.
The research marks the first time
scientists have positively created a friction-free superfluid using a gas of
fermionic atoms, atoms with an odd number of electrons, protons and
neutrons. The breakthrough happened on the night of April 13.
"It's a night I won't forget. It was
overwhelming to watch on our computers as the lithium atoms behaved in a way
that no one had ever seen before," said Dr. Wolfgang Ketterle, a Nobel
prize-winning physics professor at MIT who led the team of researchers.
To accomplish this experiment,
Ketterle's team cooled a gas cloud of lithium atoms to nearly absolute zero
(about minus 459 degrees Fahrenheit). They used an infrared laser beam to
trap the gas, then a green laser to spin it.
A normal gas simply spins, but a
superfluid can rotate only by forming quantum whirlpools. A rotating
superfluid looks like Swiss cheese; the holes are the cores of the
whirlpools. This is exactly what the MIT physicists observed that night.
In 1995, Ketterle and his team were
among the first to create a Bose- Einstein condensate, composed of bosonic
atoms that have an even number of electrons, neutrons and protons. In
Bose-Einstein condensates, particles act as one big wave, a phenomenon
predicted by Albert Einstein in 1925. That discovery earned Ketterle a
shared Nobel Prize in Physics in 2001. Bose- Einstein condensates were later
shown to be superfluids.
The new frontier became fermions.
Fermions must pair up to have an even number of electrons, neutrons and
protons, which allows them to form a Bose- Einstein condensate.
Breakthroughs at MIT and several other institutions, including Duke
University, Durham, North Carolina, produced Bose-Einstein condensation of
fermion pairs loosely bound as molecules, but found no concrete evidence of
superfluidity.
Over the past two years researchers
have been looking for the "smoking gun" for fermionic superfluidity. Despite
some hints and indirect evidence, it was not found until this research
team's discovery.
Superconductivity is superfluidity for
charged particles instead of atoms. High-temperature superconductivity is
not fully understood, but the MIT observations open up opportunities to
study the microscopic mechanisms behind this phenomenon.
"Pairing electrons in the same way as
our fermionic atoms would result in room-temperature superconductors,"
Ketterle explained. "It is a long way to go, but room-temperature
superconductors would find many real-world applications, from medical
diagnostics to energy transport," he added. Superfluid Fermi gas might also
help scientists test ideas about other Fermi systems, like spinning neutron
stars and the primordial soup of the early universe.
The MIT research was supported by the
National Science Foundation, the Office of Naval Research, the Army Research
Office, and NASA's Fundamental Physics in Exploration Systems Mission
Directorate, in support of the Vision for Space Exploration. NASA's Jet
Propulsion Laboratory, Pasadena, Calif., Pasadena, manages the Fundamental
Physics program.
The research was published in the June
23 issue of Nature. Ketterle's co- authors include grad students Schirotzek,
Schunck and Zwierlein, and former grad student Abo-Shaeer. They are all
members of the NSF-funded MIT-Harvard Center for Ultracold Atoms.
For more information about NASA's Fundamental Physics Program on the Internet, visit:
http://funphysics.jpl.nasa.gov or http://spaceresearch.nasa.gov
