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Journal of the Optical Society of America B

Exact treatment for the entanglement of the multiphoton two-qubit system with the single-mode thermal field

Faisal A. A. El-Orany

Published Aug 5, 2011• 5 citations
Publisher

Abstract

In this paper, we study the entanglement between two two-level atoms (qubits) when they interact simultaneously with a single-mode thermal field through exchanging k photons. We demonstrate the entanglement of the bipartite by making use of the concurrence. Contrary to previous studies, we deduce an exact form of the wave function of the system for various types of initial atomic states. We show that the asymmetric case (i.e., nonidentical atoms) can generate amounts of entanglement much greater than those of the symmetric one. These amounts are sensitive to the value of the transition parameter k and the type of initial atomic states. We present a novel phenomenon: for a particular type of Bell states, the initial entanglement can be trapped through the evolution of the system. This would be of a great interest in the framework of quantum memory.

DOI
10.1364/josab.28.002087

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In this paper we have investigated the dynamics of entanglement of two natural or artificial two-level atoms interacting through multiphoton transitions with a thermal field of an lossless microwave cavity. On the basis of the exact solution of the model under consideration, the atom-atom entanglement parameter for various initial separable and entangled states of atoms are found. It is shown that the interaction of atoms with the thermal field of the cavity by means of multiphoton transitions can induce entanglement for all states except for the one in which both atoms are excited. It is also established that for the initial separable states of atoms the maximum degree of entanglement increases with the multiplicity of atomic transitions.
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We have investigated the entanglement between two dipole coupled two-level artificial atoms (superconducting qubits, ion, spins etc.). The model, in which only one atom is trapped in an lossless cavity and interacts with single-mode thermal field, and the other one can be spatially moved freely outside the cavity has been carried out. We have considered the effect of the atomic coherence on the entanglement behavior. We have shown that a thermal field might cause high entanglement between the atoms both for coherent and incoherent initial atomic states only for small values of cavity mean photon number. We have also derived that the degree of entanglement is weakly dependent on the strength of dipole-dipole interaction for coherent initial states. In the considered model the atoms would get entangled even when both atoms are initially in the excited state.
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.