Nonadiabatic dynamics in the dark subspace of a multilevel stimulated Raman adiabatic passage process - art. no. 063406

In this paper we consider a generalization of the three-level stimulated Ra man adiabatic-pas sage process (STIRAP). In our scheme, there are N-1 groun d levels and one excited level. The ground levels are coupled with laser pu lses through the excited level at multiphoton resonance. The ultimate aim o f this scheme is to create coherent-superposition states on the ground leve ls. In a previous paper [J. Mod. Opt. (to be published), special issue on q uantum interference] we have considered this problem from the optimal-contr ol point of view. Here we apply a different approach: We reconsider the adi abatic approximation, which is commonly utilized to describing the STIRAP p rocess. It is shown that in our case, in the adiabatic limit, the dark and bright subspaces of the Hamiltonian are decoupled; however, the nonadiabati c corrections influence significantly the dynamics in the dark subspace. An analytic solution is presented for the case of a five-level system. Moreov er, we consider some special examples for the pulse sequences that effect p rescribed final superposition states. The robustness of the scheme is studi ed, and the extension of our scheme is also considered.