| The technique of stimulated Raman adiabatic passage (STIRAP) is a method of using partially overlapping pulses (from pump and Stokes lasers) to produce complete population transfer or to create coherent atomic superposition states in an atom or molecule. This method has been successfully extended to multilevel system. In this paper, we mainly discuss two problems.First, to reduce the transient population of the intermediate states in the adiabatic process to realize complete population transfer, a modified STIRAP method in multi-level chain system(five-level, seven-level and nine-level) of Lambda-type is discussed. During the STIRAP process, the intermediate levels will have notable population which is detrimental if these levels could decay to other levels through spontaneous emission. Here, we propose a novel method which could reduce the intermediate level population during the STIRAP process. A complete population transfer could be achieved in this modified STIRAP even if the intermediate level could decay to other levels.Secondly, we propose a scheme for creating coherent atomic superposition states via the technique of stimulated Raman adiabatic passage in a Lambda-type system where final states are composed of manifold of levels and the intermediate levels could be more than one level. If the pump pulses and Stokes pulses are kept in the same order of ordinary STIRAP, through the control of Stokes pulse intensities or Stokes and pump pulse intensities we could create arbitrary superposition states in the manifold. The experimental implementation of this method in Neon atom is given.Theoretical solutions are given and the process of population transfer and creation of superposition state are analyzed. Numerical simulation is also given and theoretical analysis is justified. The scheme proposed by us is feasible and robust. In order to achieve the above processes, two-photon resonance and adiabatic condition have to be satisfied.
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