Entanglement Dynamics Of Bipartite Open Quantum System

Quantum entanglement is one of most important physics resource in the quan-tum information process. Ideally, the people hopes that in the quantum informa-tion processes, the quantum entanglement can keep a higher degree of entangle-ment and preserve the entanglement in a long time. But in practice, every quantum system is an open quantum system which can not avoid to interact with its en-vironment. Under the condition of open quantum system, the quantum system interacts with the environment which causes decoherence, and leads to the en-tanglement decay and death. It is an important topic of quantum information processes for the study of the influence regulation of environment dissipation on the entanglement dynamics, and the avoidance of entanglement decay and death efficiently in the open quantum system. In this thesis, the entanglement dynam-ics of two partites open quantum system is investigated by using open quantum system theory and quantum entanglement theory, which has important academic meaning and application reference value. The main works and innovation points are as follows:In the first chapter, A brief introduction of the basic theory related with this thesis content is given, including the basic theory of open quantum system and quantum entanglement.In the second chapter, the population dynamics of a two-level atom un-der electromagnetic environment is investigated. Under the Markovian and non-Markovian condition, by using the time-convolutionless master equation and ex-pansing the Lamb shift and decay rate parameter by the perturbation theory, the reduce density matrix of the atom and the atomic population have been obtained. The result shows that, under the strong coupling condition, the information loses to the environment will flow back to the system partly due to the memory effect of the environment, which inhibits the decay and arises the revival phenomenon of atom population. The atomic population is protected efficiently.In the three chapter, two two-level atom system entanglement dynamics in a photonic band gap environment with double Lorentzian spectrum structures is investigated. Employing the special structure of double Lorentzian spectrum, the influence of the width of photonic band gap on the entanglement trapping is examined. The result shows that, through choosing some proper parameters, the effective suppression of the atom spontaneous decay, the preserve and trap of the entanglement in system in a long time can be realized in the double Lorentzian spectrum band gap.In the fourth chapter, the distillability entanglement dynamics of the two V-type atoms system under thermal reservoir is investigate. The realignment cri-terion is taken as a measurement of entanglement of the nine-dimensional density matrix. Through the definition of physical quantity? which is related to the re-alignment density matrix to measure the changes of the distillability entanglement. The result shows that, will decay to zero in a finite time, the free entanglement state prepared in initial time transforms to the bound entanglement, state in a finite time in the thermal reservoir, and arised the phenomenon of distillability entanglement sudden death. The preserving time of free-entangled state in system depends on the choosing of the initial parameters.In the fifth chapter, an effective methods of avoiding entanglement death, preparing ideal entanglement states, and distinguishing entanglement death sus ceptible region for two identical two-level atoms interacting with environment have been presented. Specifically, the dynamics of entanglement of two atoms initially prepared in Bell superposition states is investigated. The effect of initial excited states, initial entanglement angle and purity on the formation of entanglement are examined. A clear boundary between entanglement, sudden death region and entanglement sudden death-free region is determined. In the sixth chapter, the summary of the thesis and the outlook of this topie are given.