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Physical Review A

Effects of reservoir squeezing on the amplification of quantum correlation and the quantum speed limit

Zhaorui Peng, Lucas C. Céleri, Abdul Basit, Gao Xianlong

Published Nov 25, 2024• 5 citations
Publisher

Abstract

We examine the behavior of quantum discord in a scenario where two identical noninteracting qubits interact with a shared squeezed environment at zero temperature. Our focus lies on how the squeezing of the reservoir impacts the evolution of quantum discord when both qubits are initially in $X$-type states. We observe that there exists a critical time ${t}_{c}$ at which quantum discord undergoes a sudden change, a phenomenon crucial for quantum discord amplification. Furthermore, through numerical analysis, we determine the range of parameters where ${t}_{c}$ is finite or infinite. In cases where ${t}_{c}$ is finite, we demonstrate that increasing the squeezing phase of the bath can extend ${t}_{c}$, while increasing the squeezing strength has the opposite effect. Even in situations where ${t}_{c}$ is infinite and there is no sudden changes in the correlations, reservoir squeezing still influences quantum discord amplification, allowing adjustment of squeezing parameters to alter the time taken to reach steady-state quantum discord. Furthermore, in the short-time regime, reservoir squeezing significantly impacts the degree of quantum discord amplification. Notably, we explore the quantum speed limit time for a two-qubit system under a squeezed reservoir, finding that it can be decreased by adjusting both squeezing and the initial parameters. Our investigation offers a promising avenue for controlling quantum correlation amplification and the quantum speed limit.

DOI
10.1103/physreva.110.052433

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We examine the behavior of quantum discord in a scenario where two identical noninteracting qubits interact with a shared squeezed environment at zero temperature. Our focus lies on how the squeezing of the reservoir impacts the evolution of quantum discord when both qubits are initially in XXX-type states. We observe that there exists a critical time tc{t}_{c}tc​ at which quantum discord undergoes a sudden change, a phenomenon crucial for quantum discord amplification. Furthermore, through numerical analysis, we determine the range of parameters where tc{t}_{c}tc​ is finite or infinite. In cases where tc{t}_{c}tc​ is finite, we demonstrate that increasing the squeezing phase of the bath can extend tc{t}_{c}tc​, while increasing the squeezing strength has the opposite effect. Even in situations where tc{t}_{c}tc​ is infinite and there is no sudden changes in the correlations, reservoir squeezing still influences quantum discord amplification, allowing adjustment of squeezing parameters to alter the time taken to reach steady-state quantum discord. Furthermore, in the short-time regime, reservoir squeezing significantly impacts the degree of quantum discord amplification. Notably, we explore the quantum speed limit time for a two-qubit system under a squeezed reservoir, finding that it can be decreased by adjusting both squeezing and the initial parameters. Our investigation offers a promising avenue for controlling quantum correlation amplification and the quantum speed limit.
The dynamics of quantum discord is studied in a system of two identical noninteracting qubits coupled to a common squeezed vacuum bath through non-demolition interactions. We concern on how reservoir squeezing influences the dynamical behaviors of quantum discord when both qubits are initially prepared in XXX-type states. We find that the critical time exhibits the sudden change of quantum discord, which is of great significance for the quantum discord amplification. Furthermore, depending on the initial parameters of the system, we numerically calculate the interval when the critical time is finite or infinite. For the finite critical time, we show that the squeezing phase of the bath can prolong the critical time while the squeezing strength exhibits the opposite effect. For infinite critical time, even if there is no sudden transition point, reservoir squeezing still has an effect on the amplification of quantum discord, and the time to reach steady-state quantum discord can be changed by adjusting the squeezing parameters. Fianlly, we investigate the quantum speed limit time for a two-qubit system under squeezed reservoir, and find that the quantum speed limit time can be reduced via the adjustment of the squeezing parameters and the initial parameters. Remarkably, in the short time limit, reservoir squeezing has an obvious influence on the degree of amplification of quantum discord. Our study presents a promising approach to controlling the amplification of quantum correlation.
We investigate theoretically the dynamics of 1-norm geometric quantum correlations and their classical counterparts in a two-qubit system. Both qubits are initially prepared in Bell-diagonal states and locally coupled to separated thermal squeezed baths or a common squeezed thermal bath via energy-preserving interactions. We then unveil the effects of reservoir squeezing on the abrupt changes in the evolution of geometric correlations. It is found that adequately tuning the squeezing phase can efficiently suppress the dephasing rate and delay the appearance of sudden transitions in geometric correlations. Further, we show that the squeezing phase of the bath renders a different avenue to enhance the finite time interval for frozen quantum correlation. On the other hand, in this context, we show that the squeezing strength of the reservoir exhibits a negative role. In addition, in the common bath case, we observe the steady-state correlations and decoherence-free subspace, which can be governed via squeezing parameters. Moreover, the abrupt change from a decaying regime to a constant nonzero value in classical correlation signals the emergence of a pointer-state basis. We show that the emergence of a pointer-state basis can be delayed by suitably adjusting the bath squeezing parameters. Remarkably, we find the optimal value of the squeezing phase, which introduces maximum retardation in the appearance of a pointer-state basis.
In this paper, we investigate the quantum correlation of coupled qubits which are initially in maximally entangled mixed states in a squeezed vacuum reservoir. We compare and analyze the effects of squeezed parameters on quantum discord and quantum concurrence. The results show that in a squeezed vacuum reservoir, the quantum discord and quantum concurrence perform with completely opposite behaviors with the change of squeezed parameters. Quantum discord survives longer with the increase of squeezed amplitude parameter, but entanglement death is faster on the contrary. The results also indicate that the classical correlation of the system is smaller than quantum discord in a vacuum reservoir, while it is bigger than quantum discord in a squeezed vacuum reservoir. The quantum discord and classical correlation are more robust than quantum concurrence in the two reservoir environments, which indicates that the entanglement actually is easily affected by decoherence and quantum discord has a stronger ability to avoid decoherence in a squeezed vacuum reservoir.
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.
We investigate the dynamical evolution of quantum discord, entanglement and purity in an open quantum system of two coupled asymmetric harmonic oscillators interacting with a thermal environment. Using the Kossakowski-Lindblad master equation we analyze the time evolution starting with a squeezed vacuum state. In contrast to our previous study on entanglement evolution in asymmetric oscillators, the present work introduces XY-type position-position coupling together with a systematic joint analysis of quantum discord and purity alongside entanglement. We examine the combined effects of the squeezing parameter, asymmetry parameter, coupling constant, dissipation rate and temperature. We find that quantum discord and entanglement exhibit, in general, a non-monotonic decrease over time. Increasing temperature consistently accelerates the degradation of both quantum correlations and purity, whereas increasing dissipation accelerates the degradation of quantum correlations but leads to higher steady-state purity. Increasing the squeezing parameter provides a protective effect by enhancing initial correlations and prolonging entanglement survival time, while increasing the coupling constant leads to higher quantum correlations. The asymmetry parameter exhibits only a weak influence on the correlation evolution. Our analysis reveals that quantum discord demonstrates stronger resilience than entanglement, which can present more complex behaviour including entanglement sudden death and possible temporary revivals and re-suppressions. These findings provide valuable insights for developing robust quantum information protocols and strategies for preserving quantum correlations in realistic open quantum systems, with potential extensions to non-Markovian regimes and multi-mode architectures.
We study analytically the dynamic behaviours of quantum correlation measured by a quantum discord between two uncoupled qubits, which are immersed in a common Ohmic environment. We show that the quantum discord of the two non-interacting qubits can be greatly amplified or protected for certain initially prepared X -type states in the time evolution. In particular, it is found that stable amplification of the quantum discord exists for the case of two identical qubits, and the quantum discord can be protected for the case of two different qubits with a large detuning. It is also indicated that in general a sudden change of the quantum discord occurs in the time evolution at a critical time point t c , and the discord amplification and protection may occur only in the time interval for certain X -type states. This sheds new light on the creation and protection of quantum correlation.