SIGNIFICANT EVENTS - SCIENCE EVENTS
03/29/02
Duke Group Claims 1st in Laser-cooled Atomic Physics
The group led by PI John Thomas at Duke University is the first group to achieve degeneracy in
fermionic atoms by all-optical methods. The importance of the new result is that they are able
to trap a special two-state mixture of spin up and spin down 6Li fermions. This mixture is ideal
for studies of mechanisms of superconductivity ranging from ordinary BCS pairing to the newly
predicted resonance superfluidity which may yield the highest temperature superconductors ever
studied (in units of the Fermi degeneracy temperature TF). A magnetic trap, as used for Bose
condensation, cannot be used for these studies, since both states are repelled from the trap.
The figure below shows the experimental setup. 70W of CO2 laser power is focused to a diameter
of about 50 microns, yielding an intensity of 1.9 MW/cm2. Since the laser operates at a wavelength
of 10.6 microns, the optical scattering rate (determined by the Larmor formula) is only 2 photons/hour,
yielding an optical heating rate of only 16 picoKelvin/second. The focused beam yields a trap depth
of 0.7 mK, more than adequate to trap atoms from our 6Li magneto-optical(MOT) trap, which produces
temperatures of 150 microkelvin. After the CO2 laser trap is loaded, the optical beams of the MOT
are extinguished, and the atoms remain trapped. At any later time, a short pulse of the probe beam
yields a camera image, determining the number and temperature of the atoms
by time-of-flight.
This result sets the stage for studies of resonance superfluidity, which requires that we apply
an 850 G field to tune the elastic scattering cross section into resonance. The installation of
our high field magnets is in progress.
A paper describing these results is accepted for publication in Physical Review Letters.
