FORCE-ASSISTED VELOCITY-SELECTIVE COHERENT POPULATION TRAPPING

We present a fully quantum analysis of velocity selective coherent pop ulation trapping (VSCPT) in two schemes for which there is a force whi ch assists in the accumulation of atoms in the trapping state. In the first scheme, the F-g = 2 to F-e = 2 transition was Studied where the existence of a semiclassical polarization gradient force even for a pu re sigma(+)-sigma(-) configuration has been demonstrated which gives c ooling for blue detuning. We also verify that cooling may be obtained for the F = 2 to 1 and F = 3 to 2 transitions; our fully quantum mecha nical calculations yield a result which is consistent with recent expe rimental results of Valentin er al but differ from previous semiclassi cal calculations. Secondly, we discuss a scheme of force assisted VSCP T which combines VSCPT on the F-g = 1 to F-e = 1 transition with the c oupling to another transition for which a strong sub-Doppler cooling f orce is present. This scheme allows velocity selective coherent popula tion trapping and the polarization-gradient force to work under optimu m conditions simultaneously. We find that both of these two schemes le ad to efficient cooling of atoms.