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Entropy

Influence of the Coupling between Two Qubits in an Open Coherent Cavity: Nonclassical Information via Quasi-Probability Distributions

Abdel‐Baset A. Mohamed, Hichem Eleuch, A.‐S. F. Obada

Published Nov 21, 2019• 6 citations
Publisher

Abstract

In this paper, we investigate the dynamics of two coupled two-level systems (or qubits) that are resonantly interacting with a microwave cavity. We examine the effects of the intrinsic decoherence rate and the coupling between the two qubits on the non-classicality of different system partitions via quasi-probability functions. New definitions for the partial Q-function and its Wehrl entropy are used to investigate the information and the quantum coherence of the phase space. The amount of the quantum coherence and non-classicality can be appropriately tuned by suitably adopting the rates of the intrinsic-decoherence and the coupling between the two qubits. The intrinsic decoherence has a pronounced effect on the negativity and the positivity of the Wigner function. The coupling between the two qubits can control the negativity and positivity of the quasi-probability functions.

DOI
10.3390/e21121137

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In this paper, we investigate the dynamics of two coupled two-level systems (or qubits) that are resonantly interacting with a microwave cavity. We examine the effects of the intrinsic decoherence rate and the coupling between the two qubits on the non-classicality of different system partitions via quasi-probability functions. New definitions for the partial Q-function and its Wehrl entropy are used to investigate the information and the quantum coherence of the phase space. The amount of the quantum coherence and non-classicality can be appropriately tuned by suitably adopting the rates of the intrinsic-decoherence and the coupling between the two qubits. The intrinsic decoherence has a pronounced effect on the negativity and the positivity of the Wigner function. The coupling between the two qubits can control the negativity and positivity of the quasi-probability functions.
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.
The Wigner quasi-probability distribution function is an important tool for estimating the quantumness of quantum states. The Wigner distribution function (WDF) is related monotonically to the coherent field state density operator and their probability distributions. In this paper, we analyze the time-dependent resonator coherent field states produced by a flux qubit’s interaction with a resonator through a two-photon coupling. The WDF dynamics of the coherent field states is investigated under the effects of the qubit-resonator detuning and the intrinsic decoherence. The WDF non-classicality associated with the mixedness resonator entropy dynamics can be controlled by varying the qubit-resonator interaction, detuning as well as the decoherence. The intrinsic decoherence clearly affects the WDF non-classicality, identified by the negative values of the WDF. Finally, by fixing one or both of the complex phase space components, we are able to explore the dynamics of the Wigner-distribution functions.
We explore two coupled dipole qubits interacting with two-mode cavity fields through non-degenerate two-photon processes and under the influence of intrinsic noise. Our investigation is based on the influence of the coupling constants between different constituents of the system on the quantum coherence and entropy squeezing. We investigate the phase space information, entanglement, and purity via the Husimi function. It is found that the robustness of the positivity and the negativity of the superposition of generalized coherent state is highly sensitive to the coupling constants. The phase space quantum information, the matter-light entanglement, and the stationary mixture state can be controlled by the two-qubit coupling as well as the coupling to the environment. The effect of the intrinsic dissipation and the two-qubit coupling on the generated squeezing via the qubit-system variable squeezing or the entropy squeezing is investigated. They lead to revoke the squeezing phenomenon.
In this paper, we use the su(1,1)-algebraic treatment to explore the effects of the intrinsic decoherence in a two-mode cavity containing a two-level atom. Each field is resonant with the qubit through a four-photon process. The role of the intrinsic decoherence and the superposition of the initial generalized Barut-Girardello coherent state on the quantum effects is investigated via different quantifiers as: atomic inversion, linear entropy and negativity. It is found that the non-linearity of the four-photon process leads to generate non-classical effects with a high oscillatory behavior. The superposition of the Barut-Girardello coherent state controls the dynamics of the purity loss and the entanglement. It is found that the nonclassical effects are very sensitive to the nonlinear interactions between the qubit and the two-mode cavity.
In this paper, we explore distribution dynamics of two-qubit Fisher and skew information correlations of a dissipative microwave cavity field interacting with two charged superconducting qubits. Besides the negativity function, non-classical correlations beyond entanglement are studied using local quantum Fisher information (LQFI) and local quantum uncertainty (LQU). We find that the two-qubit non-classical correlations are sensitive to qubit–qubit distribution angle, two-qubit dissipation parameter, and initial coherent state intensity. The phenomena of frozen quantum correlations, sudden death or birth, as well as revival dynamical maps are feasible in the current two-qubit state when exposed to a microwave cavity. The non-classical correlations and entanglement have been found damped under the two-qubit dissipation appearance in the field. For the increasing strength of coherence intensity of the field, the two-qubit non-classical correlations functions remain to emerge quickly and oscillate with higher frequency, although with the least amplitudes. Interestingly, unlike the non-classical correlations, negativity does not emerge against higher coherence strengths of the cavity and remains completely zero. Finally, for the least dissipation and higher coherence strength, one can readily generate non-classical two-qubit states employing a microwave cavity.
In our work, we have explored the phase space nonlinear coherent-Kerr-cavity nonclassicality and purity loss induced by off-resonant intensity-dependent cavity-qubit interactions under atomic spontaneous-emission dissipation effect. The generation of the cavity purity loss (mixedness) dynamics, by using von Neumann entropy, is linked to the nonclassicality's Wigner distribution dynamics, which is investigated at spastic times chosen based on the von Neumann entropy's cavity dynamics. The temporal evolution of the largest negativity of the Wigner distribution is investigated under the physical system effects of the qubit spontaneous-emission dissipation, the detuning as well as the coherent-Kerr-cavity nonlinearity. The growths and the stability of the purity loss and the Wigner distribution negativity loss have the same behaviors. They depend on the Kerr-like nonlinearity and the dissipation couplings. These losses and their stability can be enhanced by increasing the dissipation coupling. It is found that the nonclassicality's phase space Wigner quasi-probability distribution and the mixedness of the generated coherent-Kerr-cavity states are highly sensitive to the physical system effects.