Research On Entanglement Dynamics In Open Quantum Systems

The quantum information has developed very fast and made a series of achievements sinceits birth in the last80’s. It has made great progress in quantum computation, quantumcryptography, quantum teleportation and quantum game theory. Quantum entanglement is thecore resource to realize quantum information, quantum computation as well as quantumcommunications. Owing to its different properties from classical mechanics, the entanglementgives rise to a general debate in the field of physics. The researches of entanglement continuenowadays and the mystery is unveiled by degrees.In the quantum world, the qubit will unavoidably interact with the environment. As theinfluence of the environment, the dynamics of quantum system may be not unitary and theentanglement may be decayed and dissipated. So, the research of entanglement dynamics andproperties in open systems seems necessary and important.According to the effect of interaction between system and environment, the dynamics canbe divided into two kinds: Markovian process and non-Markovian process. This thesis focuseson the entanglement dynamics and distribution in open systems and mainly includes thefollowing two aspects:1. We study the entanglement dynamics and transfer in a system composed of two initiallycorrelated two-level atoms, each coupled with another atom interacting with its own reservoir.There is no interaction between two subsystems. Considering the atomic dipole-dipoleinteraction, we show the entanglement transfer in Markovian and non-Markovian environmentwith different initial states. For two initial Bell-like states, the transfer of entanglement showsobviously different behaviors. We show a parameter region of dipole-dipole interaction that willspoil the entanglement birth of two initially uncorrelated atoms.2. We investigate the entanglement dynamics and distribution in a system composed of twotwo-level atoms interacting with a common reservoir. When there is just one excitation in thesystem, each mode in the reservoir can be considered as a qubit. Using the method of globalentanglement we can calculate the entanglement between atoms and reservoir modes as well asbetween the modes. We compare the difference of entanglement dynamics with and without theatomic dipole-dipole interaction. We show that the initial entanglement between atomscompletely transferring to the entanglement between reservoir modes. The entanglement will bedifferent in strong coupling regime from weak coupling regime and shift between modes withdifferent dipole-dipole interaction strengths.