Studies On Realizetion Of Quantum Dense Coding And Quantum Correlation In Two-Qubit Heisenberg Spin Systems

Quantum information is a new interdiscipline combining quantum physics and information science, which applies the basic principle of quantum mechanics to the information theory and computer science. Quantum computation can deal with some problems which are very difficult to resolve for classical computer, hence quantum information has incomparable superiority. As one of the simplest spin chains in condensed matter physics, Heisenberg spin chain becomes an effective carrier to complete the tasks of quantum information because of its good entanglement characteristic, observability and enforceability. In this thesis, we mainly investigate the quantum dense coding through a two-qubit Heisenberg spin model and analyze the quantum correlation properties in a bipartite Heisenberg spin system with Dzyaloshinskii-Moriya (DM) interaction.First of all, by solving the Milburn equation, we study the properties of optimal channel capacity for the quantum dense coding via a two-qubit Heisenberg spin system with Dzyaloshinskii-Moriya (DM) interaction in the presence of intrinsic decoherence. The influences of different DM interactions, different initial states, anisotropic coupling parameters, and intrinsic decoherence on optimal coding capacity are analyzed in detail. It is found that the initial state of the system affects optimal coding capacity greatly, whose dependent parameters are not identical for different types of initial states. When the system is initially in the form of the nonmaximally entangled state|￠(0))= 01)+<d||10), a weak z-component DM interaction can enhance the value of optimal coding capacity as compared with the value without DM interaction, and the phase decoherence effect can suppress the oscillation of optimal coding capacity and make the capacity decrease to a stable value for the long-time evolution. It is also found that under the influence of intrinsic decoherence, the optimal transmission capacity of dense coding can keep an ideal maximal value of 2 by choosing the proper initial maximally entangled state. Moreover, no matter from which direction the DM interaction is introduced, the optimal coding capacity via the two-qubit Heisenberg spin system is always larger than the transmission capacity of any classical communication.Secondly, by employing measurement induced disturbance (MID) and geometric measure of quantum discord (GMQD) as the measurement tools, we examine the properties of quantum correlation in a two-qubit Heisenberg spin system with Dzyaloshinskii-Moriya (DM) interaction taking into account the intrinsic decoherence and discuss the influence of internal and external parameters on the quantum correlations. It is found that there exists nonzero MID for separable states with zero entanglement. The quantum correlations repeatedly undergo a process of decreasing sharply and restoring quickly, however, there don’t exist phenomenon of "sudden death" no matter what kind of measurement tools are used. Moreover, different anisotropic coupling parameters have different effects on the quantum correlations, namely, small value of anisotropic parameters can enhance the correlations, while large anisotropic parameters make the correlations decrease. Furthermore when the system is initially in the form of the maximally entangled state|Ψ/(0))12=2/2(|00)+|11)), the magnetic field has no effects on quantum correlations, but for nonmaxiamally entangled states, it can change the evolution behaviors of quantum correlation remarkably.