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arXiv:0806.3884

Decoherence of two qubits coupled with one-mode cavity without rotating-wave approximation

Wang Fa-Qiang, Weici Liu, Ruisheng Liang

Published Jun 24, 2008• 0 citations
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Abstract

The decoherence of two qubits, coupled with one-mode cavity separately, has been investigated exactly. The results show that, for the resonant case, the decoherence behavior of system is similar to Markovian case when the coupling strength is weak, while the concurrence vanishes in finite time and might recover fractional initial entanglement before it permanently vanishes when the coupling strength is strong. And for detuning case, the entanglement could periodically recover after a period of time from its disappearance. These results are quite different from that of system subjected to Jaynes-Cummings model.

DOI
10.48550/arxiv.0806.3884

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The decoherence of two qubits, coupled with one-mode cavity separately, has been investigated exactly. The results show that, for the resonant case, the decoherence behavior of system is similar to Markovian case when the coupling strength is weak, while the concurrence vanishes in finite time and might recover fractional initial entanglement before it permanently vanishes when the coupling strength is strong. And for detuning case, the entanglement could periodically recover after a period of time from its disappearance. These results are quite different from that of system subjected to Jaynes-Cummings model.
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The decoherence of two initially entangled qubits coupled with a squeezed vacuum cavity separately is investigated exactly. The results show that, first, in principle, the disentanglement time decreases with the increase of squeeze parameter r, due to the augmenting of average photon number of every mode in the squeezed vacuum cavity. Second, there appear entanglement revivals after the complete disentanglement for the case of even parity initial Bell state, while there occur the entanglement decrease and the entanglement revival before the complete disentanglement for the case of odd parity initial Bell state. The results are quite different from those for the case of qubits in a vacuum cavity.
In this paper, we study the dynamics of a system consisting of two identical qubits interacting non-resonantly with a single-mode field of an ideal resonator in the presence of direct dipole-dipole and Ising interactions between the qubits. In the representation of "dressed" states, we find an exact solution of the quantum time Liouville equation for the full density matrix of the system under consideration for the initial separable and entangled states of the qubits and the thermal initial state of the resonator field. Based on the exact solution, the criterion for qubit entanglement, negativity, is calculated. The results of numerical modeling of negativity show that the inclusion of dipole-dipole and Ising coupling in the case of separable initial states of qubits can lead to a significant increase in the maximum degree of their entanglement, and in the case of entangled initial states of qubits, to stabilization of the initial entanglement. For the model with resonant interaction of qubits and the resonator field, direct interaction of qubits can also lead to the disappearance of the sudden death of entanglement effect.
The decoherence of two initially entangled qubits in a squeezed vacuum cavity has been investigated exactly. The results show that, first, in principle, the disentanglement time decreases with the increasing of squeeze parameter r, due to the augmenting of average photon number of every mode in squeezed vacuum cavity. Second, there are entanglement revivals after complete disentanglement for the case of even parity initial Bell state, while there are entanglement decrease and revival before complete disentanglement for the case of odd parity initial Bell state. The results are quite different from that of the case for qubits in a vacuum cavity.
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