Adiabatic Raman passage via two-photon resonant transitions in a five-level Λ system

We investigate a five-level Λ system for achieving the efficient population transfer between two ground-state levels without essentially populating other three intermediate excited-state levels. This five-level Λ system is found to have an approximate dark state characterized by very small (but not exactly zero) absolute eigen-values when we work in the parameter regime where all single-photon pump and Stokes transitions are well suppressed. Dynamically manipulating the approximate dark state in a proper way, we can either attain the complete population transfer from one ground-state level to another ground-state level or create the maximal coherence between the two ground-state levels. The dynamic process of a stimulated Raman adiabatic passage is implemented in fact by manipulating a two-photon resonant pump transition and a two-photon resonant Stokes transition, which is especially important when the two ground-state levels differ by Δm = ± 4 in the magnetic quantum number.