Quantum Entangled States In The Cavity QED Systems And Discussing Their Applications

Quantum inforamtion theory is one of the frontier disciplines in modern physics and informatics,and has a great deal of proud achievements.Entanglement plays a key role in quantum information theory.Entanglement is one of the most striking feature of quantum mechanics.This term "entanglement" is used for states of a composite system that can't be separated into the product of states of subsystems.Entanglement implies the correlation between separated subsystems and indicates the phenomenon of quantum nonlocality. On the other hand,entanglement is also an important resource that performs quantum information processing,such as quantum computation,quantum errorcorrecting codes,quantum dense coding and quantum teleportation.Hence, studies on quantum entanglement problems,for example,how to prepare quantum entangled states,how to measure the degree of entanglement for quantum entangled states,effect of the environment on quantum entanglement,and so on,are of significance.This thesis mainly discusses preparation of entangled states,dynamics of quantum entanglement and the application of entangled states in quantum communication.The thesis consists of seven chapters.In the first chapter,we briefly recall the developing course of quantum entanglement,present status for research of quantum entanglement.In the second chapter,we present an introduction to basic theory on quantum entanglement,including definition,measurement and judgement of quantum entanglement states.We also review some important entangled states in quantum information.In the third chapter,we describe the basic theory on cavity QED,which is the basis of our studies.In the fourth chapter,we investigate how to prepare superposition states of two-mode squeezed coherent sates in atomic ensembles interacting with cavity fields,and study non-classical properties for these superposition states.In the fifth chapter,we investigate effect of envinronment on entanglement, discuss the evolution of the linear entropies of atom-field system,in which two identical two-level atoms simultaneously interact with a single-mode dissipative cavity field under large detuning.The effects of the initial atom states and the dissipative factors of the cavity on all linear entropies are also discussed.In the sixth chapter,we present a scheme for transferring quantum information based on Jaynes-Cummings-type,interaction between two atoms,and atom and cavity field.In the last chapter,we give a simple summary to the above works and prospect applications of quantum entangled states.