NASA-funded researchers at the Massachusetts Institute
of Technology (MIT), Cambridge, Mass., have cooled sodium gas
to the lowest temperature ever recorded, one-half-billionth
degree above absolute zero. Absolute zero is the point, where
no further cooling is possible.

This new temperature is six times lower than the previous
record and marks the first time a gas was cooled below one
nanokelvin (one billionth of a degree). At absolute zero
( minus 273 degrees Celsius or minus 460 degrees Fahrenheit),
all motion stops, except for tiny atomic vibrations, since
the cooling process has extracted all energy from the

By improving cooling methods, scientists have succeeded in
getting closer to absolute zero. “To go below one nanokelvin
is like running a mile below four minutes for the first
time,” said Dr. Wolfgang Ketterle, a physics professor at MIT
and co-leader of the research team.

“Ultra-low temperature gases could lead to vast improvements
in precision measurements by allowing better atomic clocks
and sensors for gravity and rotation,” said Dr. David E.
Pritchard, MIT physics professor, pioneer in atom optics,
atom interferometry, and co-leader of the team.

In 1995, a group at the University of Colorado, Boulder,
Colo., and a MIT group led by Ketterle, cooled atomic gases
to below one microkelvin (one millionth degree above absolute
zero). In doing so, they discovered a new form of matter, the
Bose-Einstein condensate, where the particles march in
lockstep instead of flitting around independently. The
discovery was recognized with the 2001 Nobel Prize in
Physics, which Ketterle shared with his Boulder colleagues
Drs. Eric Cornell and Carl Wieman.

Since the 1995 breakthrough, many groups have routinely
reached nanokelvin temperatures; with three nanokelvin as the
lowest temperature recorded. The new record set by the MIT
group is 500 picokelvin or six times lower.

At such low temperatures, atoms cannot be kept in physical
containers, because they would stick to the walls. Also, no
known container can be cooled to such temperatures.
To circumvent this problem, magnets surround the atoms, which
keeps the gaseous cloud confined without touching it. To
reach the record-low temperatures, the researchers invented a
novel way of confining atoms, which they call a “gravito-
magnetic trap.” The magnetic fields acted together with
gravitational forces to keep the atoms trapped.

All the researchers are affiliated with the MIT physics
department, the Research Laboratory of Electronics and the
MIT-Harvard Center for Ultracold Atoms, funded by the
National Science Foundation. Ketterle, Leanhardt and
Pritchard co-authored the low-temperature paper, scheduled to
appear in the September 12 issue of Science. NASA, National
Science Foundation, the Office of Naval Research and the Army
Research Office funded the research.

Ketterle conducts research under NASA’s Fundamental Physics
in Physical Sciences Research Program, part of the agency’s
Office of Biological and Physical Research, Washington.
NASA’s Jet Propulsion Laboratory, Pasadena, Calif., a
division of the California Institute of Technology, Pasadena,
manages the Fundamental Physics program.

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More information about Ketterle’s research is available on
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