ENHANCEMENT AND SUPPRESSION OF COLLISIONS IN OPTICAL LATTICES.J. R. Lawall, C. Orzel, S. L. Rolston, and W. D. Phillips, Building 221, Room A_167, National Institute of Standards and Technology, Gaithersburg, MD 20899 (301- 975_3226, email: john.lawall@nist.gov

It has long been anticipated that the rate of collisions in an optical lattice should differ from that in a disordered sample at the same density. We study the effects of localization on collision rates in a far_off_resonant optical lattice for metastable xenon. Atoms are loaded into a traditional four_beam lattice detuned from 25 to 500 GHz. The lattice is allowed to thermalize for a time from 3 to 200 ms, at which point the atoms are released. The collision rate in the lattice is measured during and immediately after the lattice phase by counting the associated ions.

We find that the collision rate differs significantly for a lattice in which equilibrium has been achieved from that prior to equilibration. The collision rate signal shows that as equilibrium is being approached, the collision rate in the lattice is higher than that in a disordered sample, consistent with a model in which untrapped atoms are "guided" by the optical potential towards trapped atoms. For sufficiently long lattice durations, the rate of collisions in the lattice falls below that of the disordered sample, as expected for atoms trapped at discrete sites.