No abstract

Using laser light tuned to a repulsive molecular potential, we have been able to suppress inelastic ground-state hyperfine-changing collisions between ultracold R b atoms. Adiabatic excitation to the repulsive curve alters the atomic trajectories and prevents the atoms from approaching close enough for the hyperfine change to occur. Experimental results show suppressions up to -50% and are in reasonable agreement with a simple Landau-Zener model. Our ability to control collisional trap loss processes may have important implications for the achievement of high densities in laser cooled samples.

Inelastic atomic collisions constitote loss mechanihms for neutral atom traps. and the study of trap-loss rates may provide detailed information on the long-range interaction behueen atoms and on the dynamics of very slow collisions. Gallagher and Pritchard have given a simple two-state model for such collisions which includes a radiative transition or a single curve crossing at short range representing, for example. fine-structurechanging collisions. In order to better describe the more complicated case found in alkali metals, we have extended this model to include several excited hypefine structure levels with curve crossings at long range.We find that collisions in a laser field that are capable of expelling atoms from the trap can be suppressed in some laser frequency regions and enhanced in others, in comparison with the predictions of the simple two-state model. Using this model to represent radiative escape via the 2, potential of alkali dimer molecules we are able to geatly improve agreement between theory and experiment, including new measuremeals an sSRb reported here.