Quantum Entanglement And Information Process In Cavity QED And Heisenberg Spin System

Quantum entanglement is the essential physical resources of quantum computation and quantum information processes.The preparation,maintenance and manipulation of quantum entanglement play an important role in quantum computer and quantum information.Every system to realize quantum computer and quantum information has its own merit and defect.Currently,on one hand,cavity quantum electrodynamics(cavity QED) system is regarded as one of the most promising systems to realize quantum hardware,and it has been widely used in preparation and controlling of entangled state,teleportation of atomic state,operation of quantum logic gate and so on.On the other hand,Heisenberg spin system has been widely used in quantum simulation for its scalability and flexibility. In this thesis,based on cavity QED system,the realization of quantum logic gate,preparation of atomic cluster state,the entanglement dynamical properties of atoms in cavity with energy decay and the realization of concentration of quantum entangled states are investigated;based on heisenberg spin system, the thermal entanglement with or without intrinsic decoherence in heisenberg spin systems are investigated.Some original results are obtained and the main contents are as follows:In chapter 1,some basic theories of quantum information science are introduced, including the develop history of quantum information science,basic theories of quantum entanglement,quantum qubits and quantum logic gate,several common physical implementation schemes and intrinsic decoherence theory.In chapter 2,some basic theories of cavity QED and heisenberg spin systems are introduced,some common cavity QED models are deduced;compendium of heisenberg spin model,definition and measurement of thermal entanglement and relationship between entanglement and quantum phase transition are given;the main contents of this paper are introduced.In chapter 3,a physical scheme to realize quantum SWAP gate by using a large-detuned cavity QED model is proposed.Multi-atom cluster state is prepared with perfect fidelity and probability.During the interaction between atom and cavity,the cavity is only virtually excited and thus the decoherence time is largely prolonged.In chapter 4,the entanglement dynamical properties of two entangled two-level atoms interacting with a single mode field are investigated using the methods of solving master equation.The scheme to remain or amplify the entanglement of entangled states which is free of the cavity decay is found.In chapter 5,the method of concentrating non-maximally entangled states is proposed using thermal cavity QED model.The concentration of remote entangled atoms is realized by using thermal cavity QED model,and the corresponding scheme is also presented for the case of near entangled atoms.In chapter 6,the thermal entanglement properties of Heisenberg XYZ model with nonuniform magnetic field is investigated.The generation of quantum phase transition is confirmed in the ground state entanglement;When T＞0,the magnetic field can have constructive effect on the critical temperature To,we can obtain thermal entanglement at any finite T by the external magnetic field;The tendency of the thermal entanglement in the parameter spaces of(γ,ε),(γ,η),(γ,J_z) is investigated, which provides reasons to compensate control of the inner parameter with the parameter of the external magnetic field at certain temperature. In chapter 7,the thermal entanglement properties of Heisenberg XY model with intrinsic decoherence is investigated.The results show that,the entanglement can evolve to a stationary value under the intrinsic decoherence,the entanglement oscillation amplitude is squeezed by the intrinsic decoherence,and the larger the intrinsic decoherence rate,the faster the entanglement evolves to a stationary value.The magnetic field,as a most powerful tool to control the entanglement of spin systems,can have constructive effects on the entanglement of the system for certain initial states.The time behavior of the entanglement exhibits a strong dependence on the initial state of two qubits,and it can be manipulated by changing the relative phases and the amplitudes of the polarized qubits.For different initial entanglement(differentθ),the steady entanglement may be either increased or decreased in comparison with its initial concurrence by changing the relative phaseΦ.The Bell-diagonal state turns out to be a"dark"state of the system without the magnetic field.In chapter 8,the summarization and the hope are presented.