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Physica Scripta

Time-invariant discord and steady-state entanglement in engineered non-equilibrium dephasing environments

Abdul Basit, Hamad Ali, Xiaofei Yang, Guo-Qin Ge

Published Apr 26, 2021• 6 citations
Publisher

Abstract

Abstract We study theoretically the dynamics of quantum and classical correlations in the two-qubit system, locally experiencing a one-sided engineered pure dephasing non-equilibrium environment with an Ohmic class spectrum. The environmental non-equilibrium nature is characterized by random perturbations with non-stationary statistics. Particularly, we investigate the influence of the non-equilibrium feature on the protection of these correlations and, more specifically, its effect on the non-trivial phenomenon of time-invariant discord. Remarkably, we show that in the presence of this engineered non-equilibrium environment, time-invariant discord with a significantly larger magnitude exists for all Ohmic spectral densities, i.e., sub-Ohmic, Ohmic, and super-Ohmic without zero-temperature restriction. Additionally, we also show that our engineered non-equilibrium model provides a promising tool for trapping entanglement in a steady-state with a higher magnitude. Moreover, our proposed model also renders new insights for controlling decoherence through engineering the relative initial phases of the bath modes without performing any artificial operations on the main quantum system.

DOI
10.1088/1402-4896/abfb63

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Abstract We study theoretically the dynamics of quantum and classical correlations in the two-qubit system, locally experiencing a one-sided engineered pure dephasing non-equilibrium environment with an Ohmic class spectrum. The environmental non-equilibrium nature is characterized by random perturbations with non-stationary statistics. Particularly, we investigate the influence of the non-equilibrium feature on the protection of these correlations and, more specifically, its effect on the non-trivial phenomenon of time-invariant discord. Remarkably, we show that in the presence of this engineered non-equilibrium environment, time-invariant discord with a significantly larger magnitude exists for all Ohmic spectral densities, i.e., sub-Ohmic, Ohmic, and super-Ohmic without zero-temperature restriction. Additionally, we also show that our engineered non-equilibrium model provides a promising tool for trapping entanglement in a steady-state with a higher magnitude. Moreover, our proposed model also renders new insights for controlling decoherence through engineering the relative initial phases of the bath modes without performing any artificial operations on the main quantum system.
Dynamical decoupling protocols are one of the most used tools for efficient quantum error corrections and for reservoir engineering. In this paper we study the effect of dynamical decoupling pulses on the preservation of both quantum and classical correlations, and their influence on the intriguing phenomenon of time-invariant discord. We study two qubits experiencing local dephasing with an Ohmic class spectrum and subject to dynamical decoupling protocols. We investigate the connection between the dynamics of both classical and quantum correlations and the behavior of information flow between system and environment. Finally, we establish a set of necessary conditions for which time-invariant discord can be created using dynamically decoupling techniques.
We study non-Markovianity and information flow for qubits experiencing local dephasing with an Ohmic class spectrum. We demonstrate the existence of a temperature-dependent critical value of the Ohmicity parameter s for the onset of non-Markovianity and give a physical interpretation of this phenomenon by linking it to the form of the reservoir spectrum. We demonstrate that this link holds also for more general spectra. We unveil a class of initial states for which discord is forever frozen at a positive value. We connect time invariant discord to non-Markovianity and propose a physical system in which it could be observed.
We study non-Markovianity and information flow for qubits experiencing local dephasing with an Ohmic class spectrum. We demonstrate the existence of a temperature-dependent critical value of the Ohmicity parameter sss for the onset of non-Markovianity and give a physical interpretation of this phenomenon by linking it to the form of the reservoir spectrum. We demonstrate that this link holds also for more general spectra. We unveil a class of initial states for which discord is forever frozen at a positive value. We connect time-invariant discord to non-Markovianity and propose a physical system in which it could be observed.
Abstract We investigate the freezing and sudden transition in the dynamical behavior of quantum and classical correlations in a system composed of two identical non-interacting qubits locally subjected to their own non-equilibrium environments. In contrast to the equilibrium case, one can observe striking results when a bipartite quantum system couples with the non-equilibrium dephasing environment with non-stationary and non-Markovian features. Remarkably, the finite time interval in which the quantum correlation remains impervious to decoherence can be further prolonged as the environment deviates from equilibrium. This reveals that the non-equilibrium parameter provides an alternative tool to efficiently control the appearance of a sudden transition in the decay rates of correlations and their immunity towards the decoherence. Furthermore, for certain initial states, the appearance of another time-interval over which quantum correlation remains constant and the revival of classical correlation not only depends on the non-Markovianity but also on the non-equilibrium parameter.
Abstract Correlations in the open quantum systems exhibit a rich phenomenology in various decoherent environments. We theoretically study the dynamics of quantum and classical correlations in a two-qubit system, where each qubit is locally subjected to the relevant squeezed vacuum bath through the non-demolition interaction. Specifically, we unveil the effects of the squeezing phase of the bath and squeezing strength on the intriguing phenomena of freezing discord and sudden transition between classical and quantum decoherence. Remarkably, we show that by proper tuning the squeezing phase one can significantly delay the sudden transition time t ′ . Interestingly, we found that the maximum delay in t ′ may obtain when the phase difference between the squeezing phase and the phase of the coupling strength is π /2. Consequently, an increase in the t ′ leads to the enhancement of time-interval during which quantum discord does not affect by environmental noise. On the other hand, we show that squeezing strength plays a negative role in enhancing sudden transition time and preserving quantum discord. Furthermore, we also show that squeezed bath allows the existence of the time-invariant discord for a broader range of Ohmicity parameter s and initial condition ε . Strikingly our study renders new insights to control and sustain quantum correlations against the detrimental effects of decoherence beyond the conventional protocols.
Abstract The uncertainty principle sets a fundamental bound on the precision of measurement outcomes of two incompatible observables, which can be reduced in the presence of quantum memory. In this work, we investigate the dynamics of entropic uncertainty bound (EUB) for a bipartite system, where only the quantum memory is exposed to a nonequilibrium dephasing environment with an Ohmic-class spectrum, which is compared with the thermal equilibrium case. The nonequilibrium feature is defined by a nonstationary random function which can be controlled by engineering the relative initial phases of the bath modes. We show that this model renders a promising avenue for significantly suppressing the maximum steady-state value of the EUB for all the Ohmic spectral densities. Furthermore, we unveil the role of the reservoir’s Ohmic spectrum and the interplay between quantum discord and minimal conditional entropy of the measured particle in reducing the EUB. Additionally, we examine the state preparation and measurement choice condition in the engineered nonequilibrium environment case. The condition persists, and the nonequilibrium feature serves as a promising tool to impose a stronger limit on entropic uncertainty, enabling more accurate measurement outcomes under decoherence.