EXCITED-STATE SURVIVAL PROBABILITIES FOR COLD COLLISIONS IN A WEAK LASER FIELD

We show that in the cold collisions between laser-cooled and trapped a toms the probability to survive in the excited state during the collis ion can be obtained, in the weak-field limit, from a simple Landau-Zen er approach. This is shown by comparing the method with a fully quantu m and time-dependent wave-packet treatment. We also show that the opti cal Bloch equation method is not the proper semiclassical tool to use at low energies, at least in its present form. The unexpectedly low qu antum survival probability reported by Boesten et al. [Phys. Rev. A 48 , 1428 (1993)] is in fact predicted by the semiclassical Landau-Zener approach. This in turn shows that off-resonant excitation is not impor tant in the low-energy regime.