Study Of Thermal And Time Entanglement On2-Qubit And2-Qutrit Heisenberg Model System

Quantum information is the new development of information science in21st century. It is a new subject which includes classical information science and research of quantum mechanics. It enlarges the application range of quantum mechanics, while providing new principles and methods. Quantum information makes full use of basic conceptions and theories of quantum mechanics to deal with information processing. It proposes the concept of quantum entanglement, and makes quantum entanglement as one of the most significant resource.In quantum information field, the computation and analysis of local quantum entanglement of coupled Heisenberg model system is a very important issue. This thesis studies the quantum entanglement feature of system in coupled quantum dots. In Chapter2, we derive the entanglement formula of Concurrence in impure Heisenberg XX Chain and Heisenberg XXX Chain according to two cases. Calculate and analyze the thermal entanglement and time entanglement, and find obvious kinds of entanglement at different intervals, one of that has a typical transition, with the increase of impurity parameter J. At normal intervals, the thermal entanglement shows analogous evolution, but the initial entanglement and the critical temperature Tc is different, and the time entanglement shows analogous cyclical evolution. At transitional intervals, the thermal entanglement and time entanglement has significant changes, and that means the complexity of system. In Chapter3, we derive the entanglement formula of Negativity in spin-1Heisenberg XX Chain according to two cases. Calculate and analyze the thermal entanglement and time entanglement, and find it is similar to the spin-1/2Heisenberg model system on the thermal entanglement and time entanglement. No matter how the time-varying magnetic field acting on the system, the effect of parameter J is relatively large than parameter B0.