The Research On Controlled Exchange Of Quantum Entanglement State And Controlled Quantum Dense Coding

Based on the necessity and importance of the quantum information theory, this paper chooses three aspects of quantum communication to study: Von Neumann entropy of quantum entangled state, controlled exchange of quantum entangled state, controlled quantum dense coding.Firstly, there are some researches on the entropy of quantum entangled state. We calculate the evolution of Von Neumann entropy with multi-photon J-C model, and the effect if Kerr-effect on entropy of non-linearity J-C model.About the controlled exchange of quantum entangled state, there are three schemes that are presented by myself. The first is the controlled exchange of quantum entangled state of three two-level particles GHZ state. The second is controlled exchange of quantum entangled state of three two-level particles GHZ state and a W state. The third is controlled exchange atoms and the light field.There are two schemes of controlled dense coding in this paper: the dense coding in symmetric and non-symmetric channels.The five schemes are about how to control the process of quantum communication, so they can enhance the security of quantum communication, and they are very useful for the experiments of quantum communication.The results of controlled exchange of quantum entangled state and controlled dense coding have not been reported in public.