Nonlocality and purity in atom-field coupling system

The effects of initial field state and thermal environment on quantum nonlocality and linear entropy in an atom-field coupling system are investigated. We found that if the cavity is lossless and the reservoir is in vacuum, the atom-field state can exhibit quantum nonlocality periodically and the linear entropies of the atom and the field also oscillate periodically with a period the same as that of quantum nonlocality. And if the cavity dissipation is very weak and the average photon number of the reservoir is very small, the quantum nonlocality will be lost and the linear entropies of the atom and the field oscillate with a decreasing amplitude. The rapidity of the loss of the quantum nonlocality depends on the amplitude of the initial squeezed coherent state, the cavity damping constant kappa. and the average photon number N of the thermal reservoir. The stronger the field and the larger the constant kappa and the average photon number N could be, the more rapidly the nonlocality decreases.