Research On Property And Application Of Entanglement

Because of Shor's factoring algorithm and Grover's searching algorithm in the middle of 1990s,quantum computation and quantum information become one of the important research area.Quantum entanglement is a unique character of quantum system and it can be used not only for testing the basic problem of quantum mechanics but also for acting as an important resource of quantum computation and quantum information.Researchers investigate quantum entanglement carefully,for example,the essential,measurement,evolution and application of entanglement,the classification,preparation,transformation and storage of entanglement.In the thesis,I investigate dynamics of entanglement, application of entanglement in quantum information processing and proposals of realizing quantum information processing in experiment.The aim of the thesis is to understand and discuss entanglement theoretically.The content of the paper is:1.I study the dynamics of entanglement for different cases.Firstly,I investigate the evolution of entanglement when atoms interact with the cavity and show the effect of initial states on evolution of entanglement.(1)When atoms are initially prepared in GHZ class pure states,photons in the cavity can induce entanglement.(2)When atoms are initially prepared in W class pure states,the phenomenon of entanglement sudden death occurs.(3)When atoms are initially prepared in mixed states,the portion of excited-ground-ground state can induce entanglement and shorten the time of zero entanglement,while the excited state can induce the phenomenon of entanglement sudden death.(4)Furthermore,the model give an example to support two theorems between concurrence and negativity. Secondly,by using of MABK inequality,I investigate the evolution of nonlocality in antiferromagnetic environment.The phenomenon of Bell-nonlocality violation sudden death occurs and the class of decoherence-free states have been found.In the end,I investigate the effect of intrinsic decoherence of Milburn's model on entanglement of two-qutrit states.I could choose the appropriate nonlinear coupling constant to get the maximal entanglement.Study of entanglement dynamics can stave,prevent,or even control the effect of decoherence.2.I study the application of entangled states in quantum information processing. Firstly,we investigate the Dzyaloshinskill-Moriya anisotropic antisymmetric interaction and intrinsic decoherence on entanglement transfer.For some initial states m|00>+m|11> of the channel,DM interaction and intrinsic decoherence have no effect on the entanglement of the channel and output state.In other words,the channel is immunized from DM interaction and intrinsic decoherence. While for the other initial state 1/2^1/2(|01>+|10>) of the channel,DM interaction and intrinsic decoherence have obvious influence on the channel,the entanglement of the output state.Secondly,I study optimal dense coding with thermal entangled states.For two-qubit Heisenberg model,the dense coding capacity is a function of temperature and external magnetic field.Only in the case of external magnetic field being less than the coupling constant,the optimal dense coding can be realized with thermal entangled states.For two-qutrit system,I consider the dense coding capacity taking into account of nonlinear coupling constant and an external magnetic field.I find that the nonlinear coupling constant must be less than 0 for dense coding.I try to implement quantum information processing by using non-maximally entangled states.3.I show the proposal for remote implementation of partially unknown quantum operations of two qubits in cavity QED.By constructing the recovery operations of the protocol of remote implementation of partially unknown quantum operation of two qubits[An Min Wang:Phys.Rev.A 74(2006) 032317] with two-qubit Cnot gate and single qubit logic gates,all the quantum gates can be realized in cavity QED.Based on these,I present a scheme to implement remeote implementation of partially unknown quantum operations of two qubits in cavity QED.The thesis consists of four parts.In chapter 1,I introduce the relative theory of entanglement in quantum computation and quantum information.In chapter 2,the dynamics of entanglement in environment is investigated.In chapter 3,I investigate the application of entanglement in quantum information processing. In the last chapter,the scheme for remote implementation of partially unknown quantum operation of two qubits in cavity QED is shown.