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Acta Physica Sinica

Entanglement and quantum discord in a double J-C model with intensity-dependent coupling

Yao-Hua Hu, Tan Yong-Gang, Qiang Liu

Published Jan 1, 2013• 6 citations
Publisher

Abstract

Considering a double J-C model with intensity-dependent coupling, we have studied the effects of the intensity-dependent coupling, the mean photon numbers and the atomic motion, on the entanglement and quantum discord between the two two-level atoms when the moving atoms are initially in a maximally entangled state and the fields are in the single-mode thermal fields. The results show that, the entanglement and quantum discord disappear and revive periodically, and can have up to their starting values after revival. A rise in cavity temperature accelerates the death of the entanglement and quantum discord. In addition, the field-mode structural parameter has a strong effect on the entanglement and quantum discord in the system. When the field-mode structural parameter takes a suitable value, the entanglement and quantum discord of the two atoms can be kept from start to finish.

DOI
10.7498/aps.62.074202

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Abstract Considering a double JC model, this paper investigates the quantum discord dynamics of two isolated moving two-level atoms each interacting with a single-mode thermal cavity field, and studies the effect of the atomic motion and the field-mode structure on quantumdiscord. The results show that, on the one hand the quantum discord evolves periodically with time and the periods are affected by the atomic motion and the field-mode structure; on the other hand, the quantum discord still can capture the quantum correlation between the two atoms when the entanglement is zero. It is interesting to note that the quantum discord can be effectively preserved by controlling the field-mode structure parameter
In this paper we discuss two measures for the quantumness of correlations (quantum discord and entanglement) of two isolated moving atoms which are initially in Werner state. We compare and analyze the effect of the atomic motion in quantum discord and entanglement. The results show that the atomic motion related to the field mode structure parameter can make the entanglement and quantum discord evolve periodically. The results also indicate that the entanglement suddenly disappears during the evaluation but quantum discord remains non zero, so quantum discord is considered as indicator of disentanglement.
We study the dynamics of classical correlation and quantum discord of two coupled two-level atoms interacting with a cavity initially in vacuum, coherent and thermal equilibrium states, respectively. The interplay between the atom–atom coupling and mean number of photons is considered. We find that, for a cavity in a vacuum state, classical correlation or quantum discord shows a sudden change in behaviour during the evolution, and evolves periodically for zero and very large qubit–qubit couplings. However, for coherent and thermal equilibrium states, the classical correlation and quantum discord present the phenomenon of collapse–revival when the qubit–qubit coupling is much greater than the mean number of photons. The period of collapse–revival becomes long as the qubit–qubit coupling and mean number of photons increase. The relationship between quantum discord and entanglement in the studied system is considered.
By considering a double Jaynes—Cummings model, we investigate the dynamics of quantum correlations, such as the quantum discord and the entanglement, for two atoms in their respective noisy environments, and study the effect of the purity and the cavity temperature on the quantum correlations. The results show that the entanglement suffers sudden death and revival, however the quantum discord can still reveal the quantum correlations between the two atoms in the region where the entanglement is zero. Moreover, when the temperature of each cavity is high the entanglement dies out in a short time, but the quantum discord still survives for quite a long time. It means that the quantum discord is more resistant to environmental disturbance than the entanglement at higher temperatures.
Considering a double two-photon Jaynes-Cummings (J-C) model, we study the effects of Stark shift and mean photon number on entanglement between two two-level atoms when the atoms are initially in a maximally entangled state and the fields are in the single-mode thermal fields. The results show that the two atoms evolve periodically into a disentangled separable state when Stark shift is not considered. However, in the presence of Stark shift, the two two-level atoms are no longer disentangled and long-lived entanglement can be obtained. For a larger value of the Stark shift parameter and a smaller mean photon number, the two atoms can remain in a stationary entangled state. These properties show that the Stark shift can be used to control entanglement in the double two-photon J-C model under the influence of thermal environment.
The dynamical evolution of a quantum system composed of two coupled cavities, each containing a two-level atom and a single-mode thermal field, is investigated under different conditions. The entanglement between the two atoms is controlled by the hopping strength and the detuning between the atomic transition and the cavities. We find that when the atomic transition is far off-resonant with both the eigenmodes of the coupled-cavity system, the maximally entangled state for the two atoms can be generated with the initial state in which one atom is in the ground state and the other is in the excited state. When both the two atoms are initially in the excited state, the entanglement exhibits periodical sudden birth and death. By choosing appropriate parameter values, the initial maximal entanglement of the two atoms can be frozen. The relation between the concurrence and the cooperative parameter is calculated.