Adiabatic population transfer via multiple intermediate states

This paper discusses a generalization of stimulated Raman adiabatic passage (STIRAP) in which the single intermediate state is replaced by N intermedi ate states. Each of these states is connected to the initial state psi(i) w ith a coupling proportional to the pump pulse and to the final state psi(f) with a coupling proportional to the Stokes pulse, thus forming a parallel multi-Lambda system. It is shown that the dark (trapped) state exists only when the ratio between each pump coupling and the respective Stokes couplin g is the same for all intermediate states. We derive the conditions for exi stence of a more general adiabatic-transfer state that includes transient c ontributions from the intermediate states but still transfers the populatio n from state psi(i) to state psi(f) in the adiabatic limit. We present vari ous numerical examples for success and failure of multi-Lambda STIRAP, whic h illustrate the analytic predictions. Our results suggest that in the gene ral case of arbitrary couplings, it is most appropriate to tune the pump an d Stokes lasers either just below or just above all intermediate states. [S 1050-2947(99)10008-8].