Research On The Effects Of Decoherence On Dense Coding In Heisenberg Spin Chian

Quantum information, a new interdisciplinary field which involves quantum mechanics and modern information science, attracts great interest from physicists and information scientist both in theory and experiments internationally, and much work has been done. The ultimate goal of quantum information science is make quantum dense coding, teleportaion and computer possible for information and computation technology by employing quantum coherence and entanglement in essence. However, because of decoherence, quantum coherence and entanglement in quantum system decrease when implementing quantum information and computation, even vanish. Hence quantum decoherence is a main obstacle for implemention of quantum information, especially for quantum computation. How to prevent it has become one of the most important work for us.As a most fascinating freature of quantum mechanics, quanum entanglement attracts physicists attention. Wide work has been done from it`s definitions to applications and experiments. One of the most important works on entanglement is enatanglement dynamics which mainly refers to the time evolution of quantum enanglement. Work on quantum dynamics will be helpful to understad the dynamic behavior of quantum entanglement in quantum information, which provides us with exact application of quantum entanglement on quantum inforamtion. In reality the existence of decoherence leads to entanglement death and causes a change of entanglement.This dissertation is composed of four chapters and organized as follows. The first two chapters introduce the general development of quantum information theory and some fundamental knowledge relevant to quantum entanglement and coherence. Chapter 3 mainly investigates the effects of external magnetic field on quantum dense coding in a two-qubit anisotropic Heisenberg XYZ spin chain. The influences of every related parameters are studied in detail. It is found that the mean spin-spin coupling constant anisotropic parameters and play a constructive role on dense coding, but the external magnetic fieldsb and B turn out to be distrutive for this model. Moreover, the external magnetic field destroys the symmetricity of anisotropy on dense coding. Chapter 4 introduces some fundamental knowledge relevant to quantum decoherence and investigates the joint effects of phase decoherence, Dzyaloshinskii-Moriya(DM) interaction and inhomogeneity of external magnetic fieldb on dence coding capacity. It is found that a valid dence coding is always possible to use by this model when system is initially prepared in the maximum entangled state. Moreover, the optimal dense coding can be implemented for this J+ J? Jz initial state as long as the mean spin-spin coupling constannt of the XY plane is larger thanb and DM interaction despite the intrinsic decoherence. Non-maximal entangled nitial states are found to be undesirable for dence coding with this model.