The Effects Of Cavity Dissipation On Quantum Nonlocality And Purity Of Quantum State In Atom-Field Coupling System

Quantum nonlocality and purity of quantum states are not only two striking festures of quantum mechanics, but also have an important significance in quantum information science.In this thesis, we studied the effects of the initial field state and thermal environment on quantum nonlocality and purity in atom-field system, in which the field initially in the squeezed vacuum state and in the squeezed coherent state are considered respectively. It is found that if the cavity dissipation is losses and the reservoir is in vacuum, the quantum nonlocality appears periodically. When the cavity dissipation and the average photon number of the reservoir are taken into account, the initial quantum nonlocality will be lost. The rapidity of the loss of the initial quantum nonlocality depends on the amplitude of the initial field, the average photon number N and the cavity damping constant k. The stronger the field, the larger the constant and the average photon number could be, the more rapidly the nonlocality decreases.We also study the time evolution of the linear entropies of the atom, the field and the total system. It is found that in the absence of dissipation and average photon number of the reservoir the linear entropies of the atom and the field varies with time periodically , going to zero at the disentanglement times, and the period is the same as that of Bell function and the linear entropy of the total system is zero at any time. If the cavity dissipation and the average photon number of the reservoir is taken into account, the linear entropies of theatom and the field present local maxima and minima and the difference between them diminishes with time, tending to asymptotic values.