HOLD FOR RELEASE:                       NIST 96-02
Feb. 12, 1996

to coincide with presentation of                  PHYSICISTS GET HOT NEW
William D. Phillips (8:30 a.m.)                   RESULTS WITH COLD ATOMS
AAAS Annual Meeting and
Science Innovation Exposition
Baltimore Convention Center

Contact:  Linda Joy
          (301) 975-4403
          linda.joy@nist.gov

     Using some of the coldest atoms in the universe, physicists at the
National Institute of Standards and Technology have been able to observe
exotic phenomena that do not exist outside of specialized laboratories.

     Using unusual giant molecules or new forms of ultracold matter,
physicists are gaining new understandings of how nature works.

     NIST physicists recently have made significant advances using cold
atoms in experiments with optical lattices, in cold atom collisions and
in achieving the first Bose-Einstein condensation. The atomic
temperatures necessary to conduct these experiments are far colder than
the deep reaches of interstellar space, just a few millionths to a few
billionths of a degree above absolute zero.

     Such temperatures are possible using lasers and magnetic fields to
slow, cool and trap atoms. A laser beam aimed at a stream of atoms can
exert pressure against the atoms, slowing their speed and cooling their
temperature simultaneously, explains William D. Phillips, leader of
NIST's Laser Cooled and Trapped Atoms Group. Laser-cooling atoms is
analogous to spraying a stream of water at a succession of rapidly
volleyed tennis balls.

     Physicists can trap atoms in an "optical lattice" by shining lasers
at them from several different directions. The intersecting laser beams
create a periodic interference pattern, a lattice of bright and dark
regions. The light-shifted energy of the atoms is lowest in the bright
regions, so atoms caught in such an array of lasers will slip into the
bright regions as they slow down, much like eggs fit in an egg carton.

     One of the most recent accomplishments of the Phillips group is the
demonstration that an optical lattice can diffract laser light in the
same way that crystals diffract X-rays (scientists use X-rays to study
the structure of crystals). The effect is called Bragg scattering, and
it allows scientists to observe changes in the motion of trapped atoms
as they grow colder in the optical lattice.

     "We can tell how long it takes atoms in the trap to come to an
equilibrium," Phillips says. "It tells us things we couldn't measure
before about the cooling process."

     Another type of experiment, which also is allowing scientists to
measure previously unmeasurable phenomena, uses cold atoms in
collisions. For years, scientists have known that two neutral atoms are
attracted to each other due to transient shifts in their electron
orbitals. However, the force of this attraction is also influenced by
the distance between the two atoms and the time it takes the force-field
to move between the atoms, Phillips explains.

     For the first time ever, the NIST team has measured this effect.
"We can see the effect of the finite speed of light on the energy fields
of two atoms," he says. "The cold atom collisions have allowed us to see
an effect that up until now has eluded measurement."

     The physicists collided cold sodium atoms with each other while
shining a laser at them. The result is a weakly bound molecular state
that does not exist in nature, is many times larger than an ordinary
molecule and only exists in the lab for roughly 10 nanoseconds.

     Measuring the energy levels of this unusual sodium molecule has
given scientists a more accurate way to measure the lifetime of sodium
atoms. Data from experiments like this should help guide scientists
doing large-scale modeling calculations by providing benchmark data for
applications ranging from astrophysical phenomena to advances in the
lighting industry.

     Improvements in laser cooling and trapping techniques allowed
another group of researchers including Eric Cornell and Carl Wieman of
JILA, a joint program of NIST and the University of Colorado at Boulder,
on June 5, 1995, to achieve the coldest temperature ever recorded and
produce an exotic new form of matter known as a Bose-Einstein
condensate. Since then, other laboratories have reported similar
results.

     The new state of matter had been predicted decades ago by Albert
Einstein and Indian physicist Satyendra Nath Bose. In the condensate, a
gas of rubidium atoms coalesced into a single quantum state,
indistinguishable from each other, even in principle. The condensate
formed at a temperature of about 20 billionths of a degree above
absolute zero, a temperature lower than had ever been achieved
previously. Phillips expects Bose-Einstein condensates to usher in a new
era of exploration and precision measurements using cold atoms in new
ways.

     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.

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