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Chinese Physics

Nonlocality and purity in atom–field coupling system

Cai Xin, Huang Guang-ming, Gao‐xiang Li

Published Jan 27, 2005• 5 citations
Publisher

Abstract

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 κ and the average photon number N of the thermal reservoir. The stronger the field and the larger the constant κ and the average photon number N could be, the more rapidly the nonlocality decreases.

DOI
10.1088/1009-1963/14/2/001

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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 κ and the average photon number N of the thermal reservoir. The stronger the field and the larger the constant κ and the average photon number N could be, the more rapidly the nonlocality decreases.
The effects of the initial field state and thermal environment on quantum nonlocality in atom-field coupling system are investigated. It is found that if the cavity dissipation is very weak and the average photon number of thermal environment is very small, the atom-field state can exhibit quantum nonlocality periodically. The rapidity of the loss of the quantum nonlocality depends on the amplitude of the initial squeezed vacuum state and the cavity damping constant and the average photon number of thermal environment. The stronger the field is and the larger the damping constant and the average photon number could be, the more rapidly the nonlocality decreases.
The property of quantum nonlocality in the atom-field coupling system via degenerate Raman processes with cavity damping is investigated. It is found that if the cavity dissipation is very weak, the atom-field state can exhibit quantum nonlocality periodically. The rapidity of the loss of the quantum nonlocality depends on the amplitude of the initial coherent state and the cavity damping constant. The stronger the field is and the larger the damping constant could be, the more rapidly the nonlocality decreases.
Based on quantum theory, an investigation is conducted on the evolution characteristics of linear entropies of 1) atoms, 2) two cavities and 3) atom-cavity system in the interaction process of two entangled dissipative cavities and a single two-level atom which runs through one of cavities. The effect of the dissipative constant and the coupling strength of interaction between atom and cavity field on all three linear entropies is discussed for the resonant case.The results show that all three linear entropies strongly depend on the dissipative constant of cavity and the coupling strength between cavity field and atoms. Furthermore, the dissipative constant and the strength of interaction between atoms and cavity field affect not only the amplitude of the oscillation of field quantum entropy evolution but also its periodicity.
The time evolution of linear entropy of atom-field coupling system, atom and field in the system of two two-level atoms inside a single-mode cavity with amplitude-damping under the condition of large detuning were investigated. The effects of the initial preparation of two atoms, the decay rate of cavity field and the mean photon number of field on all kinds of linear entropy were discussed. The results show that if both the two atoms are in their excited states or ground states, all the linear entropies equal to zero. But when the two atoms are in their coherent superposition state of excited state and ground state, the cavity dissipation will lead to the system to evolve into a mixed state, the linear entropy of atom and field exhibits periodic oscillations with damped amplitude.
The density operator was induced via V-type atom interacting with a cavity-field through Raman process system in an amplitude damping cavity, and the properties of linear entropies for atom-field system for atom and for field in the system were investigated. The results show that the linear entropy of the system and atom are larger than zero except the initial time in a dissipative cavity. The values remain a certain degree after some time and increase with the increase of mean photon number. At t_d, the atom is completely decoherent to the cavity. The field comes back to the initial pure state. But the atom is still in a mixed state. The larger the dissipation, the more rapid the linear entropies of the atom and system tend to the certain degree of mixture. And the larger the mean photon number, the more obvious the dissipation influence on the linear entropy.