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Journal of the Korean Physical Society

Wehrl information and mixedness of a Cooper-pair box coupled to a cavity in a thermal reservoir

Abdel‐Baset A. Mohamed, Hichem Eleuch

Published Feb 1, 2016• 4 citations
Publisher

Abstract

An analytical description of a Cooper-pair box coupled to a dissipative cavity in a thermal bath is derived. The Wehrl entropy and the Wehrl density are used to investigate the dynamics of the mixedness and the information loss of the phase space for the state of the Cooper-pair box. We show that the Wehrl entropy and density are very sensitive not only to the damping rate and the number of thermal photons but also to the intensity of the coherent state and the qubit distribution angle of the initial state. The information of the phase space and the coherence are quickly lost due to the thermal photons.

DOI
10.3938/jkps.68.513

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An analytical solution for a dissipative cavity field interacting with two qubits (TQs) in presence of Kerr-like medium is obtained. The super-operator method is used to obtaining the field density matrix elements under the dispersive approximation. Linear entropy is calculated to determine the entanglement between the cavity field and the TQs. Moreover, the Wehrl entropy and Wehrl phase distribution are discussed to discover the nonclassicality dynamics of a dissipative cavity field. It is found that the Kerr medium and the dissipation reduce the generated quantum coherence due to the qubit–cavity interactions. It is possible to control the ability of cavity–qubit interactions to generate quantum coherence by the mean photon number of the initial coherent cavity state. Moreover, the nonclassicality of the initial coherent state reduces the dissipative and the Kerr medium effects.
A system of a superconducting charge qubit with gate change ne≠12 interacting with a single-mode microwave cavity field, coupled to its reservoir, is introduced. The system is transformed into the usual Jaynes–Cummings model by canonical transformation. Analytical and numerical results under certain parametric conditions are obtained by means of which we analyze the influence of the damping terms and the detuning on the dynamics of Wehrl entropy and purity loss of the states. The results indicate the sensitivity of these aspects to change either in the decay or in the detuning parameters. An interesting relation between the correlation and decoherence effect is observed.
This study explores the dynamics of atomic mixedness and phase space quasi-probability information of one of two moving atoms trapped in a cavity filled by a coherent field. The atom-photon interactions are considered with the resonance case through nonlinear intensity-dependent coupling. We investigate the impacts of the atom-photon and atomic motion couplings on the dynamics of the atomic Wehrl entropy's mixedness and phase space Husimi distribution information. By helping Wehrl entropy's mixedness dynamics, the dynamics of acceleration and enhancement of the generation of the atomic phase space quasi-probability coherence are examined, and the Husimi distributions of the generated atomic states of one of the two moving atoms are explored. The results are shown that the atomic Husimi distribution and Wehrl entropy's mixedness are susceptible to an increase in the atom-photon and the atomic motion couplings. Therefore, the atomic phase space Husimi distribution coherence can be improved by increasing the atomic motion and nonlinear atom-photon couplings.
We explore the phase space quantum effects, quantum coherence and non-classicality, for two coupled identical qubits with intrinsic decoherence. The two qubits are in a nonlinear interaction with a quantum field via an intensity-dependent coupling. We investigate the non-classicality via the Wigner functions. We also study the phase space information and the quantum coherence via the Q-function, Wehrl density, and Wehrl entropy. It is found that the robustness of the non-classicality for the superposition of coherent states, is highly sensitive to the coupling constants. The phase space quantum information and the matter-light quantum coherence can be controlled by the two-qubit coupling, initial cavity-field and the intrinsic decoherence.
Analytical description for a Su(2)-quantum system interacting with a damped Su(1, 1)-cavity, which is filled with a non-linear Kerr medium, is presented. The dynamics of non-classicality of Su(1, 1)-state is investigated via the negative part of the Wigner function. We show that the negative part depends on the unitary interaction and the Kerr-like medium and it can be disappeared by increasing the dissipation rate and the detuning parameter. The phase space information of the Husimi function and its Wehrl density is very sensitive not only to the coupling to the environment and the unitary interaction but also to the detuning as well as to the Kerr-like medium. The phase space information may be completely erased by increasing the coupling to the environment. The coherence loss of the Su(2)-state is investigated via the Husimi Wehrl entropy. If the effects of the detuning parameter or/and of the Kerr-like medium are combined with the damping effect, the damping effect of the coupling to the environment may be weaken, and the Wehrl entropy is delayed to reach its steady-state value. At the steady-state value, the phase space information and the coherence are quickly lost.