FOR IMMEDIATE RELEASE:                  NIST 94-30
Aug. 15, 1994

Contact:  Linda Joy                     NIST PHYSICISTS MEASURE
          (301) 975-4403                COLDEST TEMPERATURE EVER

     GAITHERSBURG, Md.--If it's too hot outside, a visit to
the National Institute of Standards and Technology might provide
some relief.  Physicists here recently cooled atoms to 700
nanokelvins, the coldest temperature ever recorded for matter.

     NIST scientists chilled a cloud of cesium atoms very close
to absolute zero using lasers to catch the atoms in an optical
lattice.  The atoms reached 700 nanokelvins, or 700 billionths of
a degree above absolute zero.  Zero kelvin (minus 273 degrees
Celsius), or absolute zero, is the temperature at which atomic
thermal motion would cease.

     Since the late 1970s, physicists have sought to use lasers
to cool atoms to as close to absolute zero as possible, primarily
for improving atomic timekeeping.  Super-cold atoms also can be
used to improve certain experimental measurements.  They are
manipulated more easily than room-temperature atoms, and they may
improve lithography processes for the semiconductor industry.

     Since laser cooling was first demonstrated at the NIST
laboratories in Boulder, Colo. in 1978, scientists around the
world have been steadily pushing to lower temperatures.  In 1985,
researchers thought a theoretical limit had been reached when
sodium atoms were cooled to 240 microkelvins (240 millionths of a
kelvin).

     Surprisingly, a few years later, a team at NIST
in Gaithersburg measured sodium temperatures as low as
25 microkelvins.  New theories led to a better understanding of
laser cooling and allowed a collaboration, between NIST and
researchers at the Ecole Normale Sup‚rieure in Paris, to cool
cesium atoms to 2.5 microkelvins in Paris.

     Their record stood as the coldest steady-state temperature
for three-dimensional motion of atoms until the recent NIST work,
although other researchers achieved lower temperatures
transiently, or in one or two dimensions.

     The new record low temperature at NIST was achieved with a
technique borrowed from the Paris laboratory:  an arrangement of
four laser beams interfering to produce a regular array, or
"optical lattice" of microscopic hills and valleys for the atoms.

     The NIST team, which includes physicists Anders Kastberg,
Steven Rolston, Robert Spreeuw, Poul Jessen and group leader
William Phillips, found that atoms became trapped in the valleys
of the optical lattice and reached temperatures close to
1 microkelvin.  The trapped atoms oscillate back and forth around
the bottoms of the valleys.  To reduce the temperature of the
atoms even more, the scientists reduced the intensity of the
light.  As the laser light fades, the terrain of the optical
lattice becomes less steep, slowing the frequency of the
oscillations.  This phenomenon, known as adiabatic expansion,
drives the atomic temperature even lower, where the typical
atomic velocity is only 7 millimeters per second.

     So how did the NIST team measure such a cold temperature?
After the atoms reached the lowest temperature possible in the
optical lattice, the scientists abruptly turned off the lasers.
By measuring how far the atoms moved in a specified amount of
time, the scientists were able to calculate their temperature.
Now, the NIST researchers are working to apply their discovery in
new and better atomic clocks.

     As a non-regulatory agency of the Commerce Department's
Technology Administration, NIST promotes U.S. economic growth by
working with industry to develop and apply technology,
measurements and standards.

                                   -30-