Research On The Effects Of Decoherence On Quantum Discord And Dense Coding In One-Axis Twisting Model

With the development of science and technology, quantum information had a good development in each branch, they are established on the basis of the quantum information.Perhaps the most prominent research is quantum entanglement. Entanglement is a uniquely quantum mechanical resource that plays a key role in many of the most interesting applications of quantum information. Such as the study of quantum dense coding and quantum teleportation not only has made a great progress in the field of physics, but has obtained better use in the medical and military realm. Therefore, people are keen on the study of quantum entanglement in recent years. For a long time, quantum entanglement has traditionally been thought of as equivalent to the quantum correlation. It is considered to be the cause of the quantum computing is superior to the classical computing. However, with the emergence of quantum discord(QD), let people realized that there is a better correlation that can reflect the nature of quantum. Since then, the research of quantum discord become a hot topic. In the process of the researchers for quantum information processing. Tending to set the quantum system in the closed state, ignored the interaction between the environment and the system, the effects of the decoherence.Based on the above reasons, in this thesis, we study the effects of decoherence on quantum discord and dense coding in one-axis twisting model. In Chapter I, the general situation of quantum information have been summarized, the major research subjects and the organization of the dissertation are given at the end of this chapter. In Chapter 2, the importance of quantum correlation and the different correlation measures (C and QD) are introduced. In the end, the relevant theories of quantum dense coding are introduced. In Chapter 3, quantum discord behaviors in one-axis twisting model with intrinsic decoherence are investigated. It is found that the magnitude of quantum discord is strongly dependent on the initial states, the squeezing interaction μ, the magnetic field Ω and the purity r of initial states. With t→∞ one can obtain the steady quantum discord (SQD) value, the environmental decoherence cannot entirely destroy the quantum correlation. Varying the parameters μ,Ω and r not only can weaken the effects of decoherence but also can improve the magnitude of QD and SQD. The values of QD and SQD are improved with increasing r . Properly tuning the parameters μ, Ω and r , one can obtain a desired value of QD or SQD. In Chapter 4, quantum dense coding in one-axis twisting model under intrinsic decoherence with different initial states (Werner state and Bell state) is investigated.It shows that dense coding capacity X oscillates with time and finally reaches different stable values. X can be enhanced by decreasing the magnetic field Ω and the intrinsic decoherence y or increasing the squeezing interaction μ, moreover, one can obtain a valid dense coding capacity by modulating these parameters. The stable value of X reveals that the decoherence cannot entirely destroy the dense coding capacity. In addition, decreasing Ωor increasing μ not only can enhance the stable value of χ , but also can impair the effects of decoherence. For the initial state is Bell state, the large spin squeezing interaction compared with the magnetic field guarantees the optimal dense coding. One cannot always achieve a valid dense coding capacity for the Werner state, while for the Bell state, the dense coding capacity χ remains stuck at the range of greater than 1 ( a valid dense coding).