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Journal of Physics A Mathematical and Theoretical

Enhanced quantum nonlocality induced by the memory of a thermal-squeezed environment

Po‐Wen Chen, Md. Manirul Ali, Shiaw-Huei Chen

Published Sep 2, 2016• 3 citations
Publisher

Abstract

Abstract We investigate the transient non-Markovian dynamics of quantum nonlocality for a pair of two-level atoms coupled to a common thermal-squeezed environment. We use Bell-CHSH inequality, steering inequality, and entanglement as theoretical tools to investigate the nonlocality dynamics. We see significant differences between the non-Markovian nonlocality dynamics and its Markovian counterpart. We mainly focus on quantum steering nonlocality which has gained much interest recently. An enhanced quantum nonlocality is shown through the violation of steering inequality and entanglement in the non-Markovian regime of the structured environment. A close correspondence is shown between steering nonlocality and entanglement dynamics.

DOI
10.1088/1751-8113/49/39/395302

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Abstract We investigate the transient non-Markovian dynamics of quantum nonlocality for a pair of two-level atoms coupled to a common thermal-squeezed environment. We use Bell-CHSH inequality, steering inequality, and entanglement as theoretical tools to investigate the nonlocality dynamics. We see significant differences between the non-Markovian nonlocality dynamics and its Markovian counterpart. We mainly focus on quantum steering nonlocality which has gained much interest recently. An enhanced quantum nonlocality is shown through the violation of steering inequality and entanglement in the non-Markovian regime of the structured environment. A close correspondence is shown between steering nonlocality and entanglement dynamics.
Quantum systems are inherently open and fragile, leading to the loss of information and quantum properties to the environment. This study investigates the behavior of quantum entanglement (QE), quantum nonlocality (QN), and measurement uncertainty in a two-atom system interacting with a common dissipative thermal reservoir under the Markovian approximation. QE is measured using concurrence, QN through the CHSH-Bell inequality, and uncertainty through the quantum memory-assisted entropic uncertainty relation (QMA-EUR). The findings show that both QE and QN decay as the scaled time and excitation numbers increase, with QE being more resilient. In contrast, QMA-EUR shows an anticorrelation with concurrence and CHSH-Bell violation, increasing as these properties diminish. Adjusting the system initial-state parameters improves QE and CHSH degree of violation, while reducing uncertainty. Over long durations, concurrence and CHSH-Bell violations disappear, while QMA-EUR stabilizes at its maximum value. These results highlight the importance of precise parameter control to enhance quantum features and predict outcomes, especially for bipartite systems initialized in a Werner-like state.
In this paper, we explore the dynamics of nonlocal correlations in a two-qubit system, that is, first prepared in a Gisin state and then interacts with a bosonic non-Markovian environment. We employ uncertainty-induced nonlocality (UIN) and the Horodecki measure (Bell function) to characterize the degree of nonclassical correlations and quantum nonlocality in the system, taking into account the influence of the non-Markovian reservoir. The dynamics of the UIN and the Bell nonlocality are next examined using the various parameters that define the non-Markovian reservoir and the initial Gisin state. Our results show that the amount of nonlocal correlations and the degree of violation of Bell’s inequality can be modulated by varying the physical parameters characterizing the non-Markovian reservoir and the initial Gisin state. We also show that in some specific cases, the system exhibits nonclassical correlations while the evolved Gisin state does not violate Bell’s inequality. Our results also confirm that UIN is robust than Bell’s nonlocality in the presence of decoherence induced by the interaction with the non-Markovian reservoir.
We investigate nonlocal quantum correlations arising between multiple two-level impurity atoms coupled to an ultracold bosonic gas. We find that the environment-induced dynamics of the impurity subsystem can generate nonlocal states that are robust against noise and violate a multipartite Bell inequality when projective spin measurements are made. Genuine multipartite nonlocality is also observed in a system of three impurities. We show that non-Markovian effects, and the persistence of coherences in the impurity subsystem, are crucial for preventing complete loss of nonlocality and allow for nonlocal correlations to be generated and maintained for extended periods of time.
Abstract We investigate the dynamics of steerable weight and quantum nonlocality in a driven system consisting of two independent two-state system, within the framework of non-Markovian dissipative processes. The influences of memory effects, classical driving, and detunings on both steerable weight and nonlocality are examined by obtaining an exact solution of the system dynamics under the rotating-wave approximation. By comparison with the results obtained in the presence of Markovian dissipation, we reveal that classical driving can significantly enhance both steerable weight and nonlocality in the non-Markovian regime. Moreover, even in the presence of non-Markovian dissipation, the values of steerable weight and nonlocality can be maintained for a prolonged duration with the assistance of classical driving. Remarkably, our results demonstrate that the enhancement and preservation of steerable weight and nonlocality strongly depend on the combined effects of classical driving and non-Markovian effects.
We theoretically study the non-Markovian dynamics of qubit systems coupled to nonequilibrium environments with nonstationary and non-Markovian statistical properties. The reduced density matrix of the single qubit system satisfies a closed third-order differential equation with all the higher-order environmental correlations taken into account and the reduced density matrix of the two qubit system can be expressed as the Kraus representation in terms of the tensor products of the single qubit Kraus operators. We derive the relation between the entanglement and nonlocality of the two qubit system which are both closely associated with the decoherence function. We identify the threshold values of the decoherence function to ensure the existences of the concurrence and nonlocal quantum correlations for a given evolution time when the two qubit system is initially prepared in the composite Bell states and the extended Werner states, respectively. It is shown that the environmental nonstationary feature can suppress the decoherence and disentanglement dynamics and can reduce the coherence and entanglement revivals in non-Markovian dynamics regime. In addition, it is shown that the environmental non-Markovian feature can enhance the coherence revivals in the single decoherence dynamics and the entanglement revivals in the two qubit disentanglement dynamics, respectively. Furthermore, the environmental nonstationary and non-Markovian features can enhance the nonlocality of the two qubit system.
Knowledge of the dynamical behavior of correlations with no classical counterpart, like entanglement, nonlocal correlations and quantum discord, in open quantum systems is of primary interest because of the possibility to exploit these correlations for quantum information tasks. Here we review some of the most recent results on the dynamics of correlations in bipartite systems embedded in non-Markovian environments that, with their memory effects, influence in a relevant way the system dynamics and appear to be more fundamental than the Markovian ones for practical purposes. Firstly, we review the phenomenon of entanglement revivals in a two-qubit system for both independent environments and a common environment. We then consider the dynamics of quantum discord in non-Markovian dephasing channel and briefly discuss the occurrence of revivals of quantum correlations in classical environments.