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 figure below shows the experimental setup.

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.