Cavity Qed Atom Entanglement Evolution And Control

In 1935, Einstein, Podolsky and Rosen brought forward the famous EPR correlation. Since then the concept of quantum entanglement state was given birth to. Entanglement is one of the most striking features of quantum mechanics, and plays key pole in quantum information science. But in quantum information process, because of the inevitable couple between the quantum system and environment, the quantum system loses its quantum characteristics such as entanglement, coherence and nonlocality if it is open to the environment. It is important to study how the quantum property such as entanglement, coherence, and nonlocality evolve with time and how to prevent decoherence from system state .In this paper, we mainly investigate the decoherence in the interact system of atom and field, this thesis contains two parts:1. We investigate the time evolution of the entanglement between two atoms and the maximal violation of Bell-CHSH inequality. Considering the interaction between two two-level atoms and a single-model field, we find an exact solution of the Milburn equation for the system. The influence of dipole-dipole interaction and detuning between the caving and the atom on the entanglement and Bell violation has been discussed .The effect of dipole-dipole interaction between two atoms on the entanglement and Bell inequality violation is obvious; with the detuning increases, the entanglement between two atoms and Bell inequality violation will become larger and we find that the stationary value of the entanglement between two atom only depends on the difference between the dipole- dipole coupling intensity and the detuning . The Bell inequality violation and the entanglement does not satisfy the monotonous relation, a large Bell inequality violation corresponding to a little amount of entanglement.2. We investigate the time evolution of the entanglement between two atoms which driven by thermal field. Considering the interaction between two two-level atoms and a single-model decay field, we find an exact solution of the master equation for the system. The influence of effect photon number, coupling coefficient between the caving and the atom and atom's initial state on the entanglement has been discussed. Through controlling the effect photon number, coupling coefficient and atom's initial state ,we can get the different evolution regulation .The entanglement between two atoms can be suppressed by arising the effect photon number ,coupling coefficient . The time evolution of the entanglement can change a lot with the atom's initial state.