SIMPLE QUANTUM-MECHANICAL PICTURE OF COLD OPTICAL COLLISIONS

We present a quantum-mechanical study of the dynamics of collisions of cold atoms in a (magneto-) optical trap valid in the linear intensity regime. We find further evidence for a discrepancy with results of th e semiclassical optical-Bloch-equation method at lower collision energ ies and detunings, referred to as ''quantum suppression'' in previous work. We find a strong dependence on the detuning: for the lowest ener gies considered the suppression factor ranges from more than three ord ers of magnitude for DELTA = -GAMMA(at) to a factor 2 at DELTA = -10GA MMA(at). The fraction of atoms surviving at small interatomic distance s for a single l value can in good approximation be described by a sim ple formula in the form of a product of a Landau-Zener excitation func tion and a WKB survival factor. Summed over partial waves this formula allows a relatively easy calculation of loss rates in a two-channel l inear-intensity description. The role of such an approach in a future more complete treatment including hyperfine channels is pointed out.