Preparation Of Entangled States Of Atomic Ensembles In Cavity QED System

Quantum information, as a comprehensive subject of quantum mechanics and information science, has a broad theoretical research value and application prospect. As the resource of quantum information, quantum entanglement has been studied thoroughly, which is not only significant to understand the features of quantum mechanics, but also of great value to the development of the method new quantum information processing. In this paper, we focus on the preparation of entangled states of atomic ensembles in cavity quantum electrodynamics (QED) system. The main contents are as follows:In the first chapter, we firstly introduce some basic concepts and theory of quantum information and the application of quantum entanglement. Then we introduce an important physical system for preparation of entangled states-cavity QED. Finally, we take the simplest A type of energy system for example to analyze stimulated Raman adiabatic process (STIRAP), which illustrates the unique advantages of the adiabatic process on the quantum control.In the second chapter, we propose a scheme for generation of the W state and the Greenberger-Horn-Zeilinger (GHZ) state of atomic ensembles. The scheme is based on the dynamics of a single control atom and atomic ensembles interacting with a nonresonant cavity mode. The required time for preparing the W state (GHZ state) keeps unchanged (increases linearly) with the increase of the number of atomic ensembles. The effects of dissipation and the detuning between the atomic modes and the control atom on the prepared states are analyzed by numerical simulation.In the third chapter, we propose a potentially practical scheme for creating entanglement between two atomic ensembles in two coupled cavities via adiabatic passage. By choosing appropriate parameters, the effective Hamiltonian describes two atomic ensembles interacting with the same cavity mode and has a dark state. Consequently, the entanglement between the two ensembles is gained via adiabatic passage. Numerical calculations show that the scheme is robust against moderate fluctuations of the experimental parameters. In addition, the effect of decoherence can be suppressed effectively.In the fourth chapter, we propose a way to prepare W state among atomic ensembles collectively controlled by a single atom via adiabatic passage. The atomic ensembles are trapped in spatially separated cavities collectively linked to another cavity trapping a single atom by optical fibers. Our strictly numerical simulations show that, the atomic spontaneous emission, the cavity decay and the fiber loss are efficiently suppressed by the engineering adiabatic passage. The method can be generalized to prepare W state among any number of atomic ensembles.