Adiabatic Population Transfer In Atomic System

In many researches on micro systems, like these connected with atomic or molec-ular systems, including the fields such as quantum optics, quantum information and quantum computation, atomic physics, atomic optics, molecular physics, condensed matter physics, high-energy physics, material physics, etc., quantum coherent super-position states are the basic resources, which are the essence of many interesting phe-nomena. How to prepare atomic or molecular systems in our required quantum su-perposition states is significant task either for researches on quantum superposition itself or for its applications, such as electromagnetically induced transparency (EIT), lasing without inversion, the enhancement of the refractive index, adiabatic population transfer, subrecoil laser cooling, and atom interferometry,etc.Quantum superposition states indicate that atomic or molecular systems can be in different single states at the same time with respective probability less than 1. In fact, preparing different quantum superposition is also a process of population trans-fer. Different population transfer methods are listed in chapter 1, from the decoherent optical pumping to widely used stimulated Raman adiabatic passage (STIRAP) tech-nique based on dark states, from diabatic transfer processes to recent adiabatic ones. Recently we can use coherent laser fields instead of decoherent lamp light, and use adiabatic population transfer methods with efficiency almost 100% instead of former low-efficiency diabatic ones. More and more effective methods are adopted.An method for adiabatic population transfer and the preparation of an arbitrary quantum superposition state using the oscillating dark states (ODS) in atomic system is presented in chapter 2. Quantum state of a three-level (?) configuration atomic system finally evolves into the same time-dependent state, and oscillates periodically between two ground levels under evolving adiabatic conditions when two pairs of classical detuning laser fields drive the system into the ODS forcedly, whatever the initial states of the system are. The decoherence of the ODS evolution is greatly suppressed and the oscillation is very stable, therefore adiabatic population transfer and the preparation of an arbitrary quantum superposition state of atomic system can be completed accurately and conveniently.In chapter 3, we propose a method for the creation of arbitrary superposition of N atomic states using generalized stimulated Raman adiabatic passage (STIRAP) techniques with laser fields coupling each one of N lower states to a single upper state in a (N+1)-level atomic system. (N-1) dark states that are composed of N lower states span a dark subspace. In the adiabatic limit, the dark and bright subspaces are decoupled, thus the nonadiabatic interaction within this dark subspace dominates the evolution of the system. Differernt from general methods to create our required coherent superposition state, in a reverse way, we here consider the required state as the starting point of evolution dynamics, and utilize laser fields to drive it into a single lower state step by step. Time reverse pulses of laser fields return the single lower state back to our required coherent superposition state based on time reversal symmetry. In principle, the computationally simple method allows the case with large value of N. Based on the STIRAP techniques, it is robust against small variations of parameters of laser pulses and is immune to spontaneous radiation.