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].