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Dynamics of correlations due to a phase noisy laser

Bruno Bellomo, Rosario Lo Franco, Erika Andersson, James D. Cresser

Published Aug 14, 2016• 25 citations
OpenAlex

Abstract

We analyze the dynamics of various kinds of correlations present between two initially entangled independent qubits, each one subject to a local phase-noisy laser. We give explicit expressions for the relevant quantifiers of correlations for the general case of single-qubit unital evolution, which includes the case of a phase-noisy laser. Although the light field is treated as classical, we find that this model can describe revivals of quantum correlations. Two different dynamical regimes of decay of correlations occur, a Markovian one (exponential decay) and a non-Markovian one (oscillatory decay with revivals) depending on the values of system parameters. In particular, in the non-Markovian regime, quantum correlations quantified by quantum discord show an oscillatory decay faster than that of classical correlations. Moreover, there are time regions where nonzero discord is present while entanglement is zero.

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We analyze the dynamics of various kinds of correlations present between two initially entangled independent qubits, each one subject to a local phase-noisy laser. We give explicit expressions for the relevant quantifiers of correlations for the general case of single-qubit unital evolution, which includes the case of a phase-noisy laser. Although the light field is treated as classical, we find that this model can describe revivals of quantum correlations. Two different dynamical regimes of decay of correlations occur, a Markovian one (exponential decay) and a non-Markovian one (oscillatory decay with revivals) depending on the values of system parameters. In particular, in the non-Markovian regime, quantum correlations quantified by quantum discord show an oscillatory decay faster than that of classical correlations. Moreover, there are time regions where nonzero discord is present while entanglement is zero.
We analyze the dynamics of various kinds of correlations present between two initially entangled independent qubits, each one subject to a local phase-noisy laser. We give explicit expressions for the relevant quantifiers of correlations for the general case of single-qubit unital evolution, which includes the case of a phase-noisy laser. Although the light field is treated as classical, we find that this model can describe revivals of quantum correlations. Two different dynamical regimes of decay of correlations occur, a Markovian one (exponential decay) and a non-Markovian one (oscillatory decay with revivals) depending on the values of system parameters. In particular, in the non-Markovian regime, quantum correlations quantified by quantum discord show an oscillatory decay faster than that of classical correlations. Moreover, there are time regions where nonzero discord is present while entanglement is zero.
In this paper, we investigate the time evolution of quantum correlations in a two-qubit system influenced by an optical channel. The system?s dynamics are analyzed in terms of concurrence (CN), Bell non-locality (BN), and trace distance discord (TDD), which quantify entanglement, non-local correlations, and quantum discord, respectively. Our model explores the impact of key parameters such as the beam-splitter angle, ?, channel parameter, ?, and angular frequency, ?, on these quantum correlations. The results show that CN and BN exhibit oscillatory behavior with periodic revivals, but tend to decay more rapidly under noisy conditions. Conversely, TDD demonstrates greater robustness, persisting even when CN and BN collapse, indicating the survival of quantum correlations in separable states. Higher noise strength and angular frequencies induce faster oscillations and revivals across all measures, with systems prepared with stronger initial quantum correlations showing increased resilience. This study highlights the robustness of quantum discord in noisy environments and its potential role in quantum information processing, even in the absence of entanglement.
We address the effect of classical noise on the dynamics of quantum correlations, entanglement and quantum discord (QD), of two non-interacting qubits initially prepared in a Bell state. The effect of noise is modeled by randomizing the single-qubit transition amplitudes. We address both static and dynamic environmental noise corresponding to interaction with separate and common baths in either Markovian and non-Markovian regimes. In the Markov regime, a monotone decay of the quantum correlations is found, whereas for non-Markovian noise sudden death and revival phenomena may occur, depending on the characteristics of the noise. Entanglement and QD show the same qualitative behavior for all kind of noises considered. On the other hand, we find that separate and common environments may play opposite roles in preserving quantum correlations, depending on the noise regime considered.
Revivals of quantum correlations have often been explained in terms of back-action on quantum systems by their quantum environment(s). Here we consider a system of two independently evolving qubits, each locally interacting with a classical random external field. The environments of the qubits are also independent, and there is no back-action on the qubits. Nevertheless, entanglement, quantum discord, and classical correlations between the two qubits may revive in this model. We explain the revivals in terms of correlations in a classical-quantum state of the environments and the qubits. Although classical states cannot store entanglement on their own, they can play a role in storing and reviving entanglement. It is important to know how the absence of back-action, or modeling an environment as classical, affects the kind of system time evolutions one is able to describe. We find a class of global time evolutions where back-action is absent and for which there is no loss of generality in modeling the environment as classical. Finally, we show that the revivals can be connected with the increase of a parameter used to quantify non-Markovianity of the single-qubit dynamics.
The non-Markovian decoherence of quantum and classical correlations is analytically obtained when two qubits are asymmetrically subjected to the bit flip channel and phase flip channel. For one class of initial mixed states, quantum correlations quantified by quantum discord decay synchronously with classical correlations. The discovery that the decaying rates of quantum and classical correlations suddenly change at the characteristic time is physically interpreted by the distance from quantum state to the closest classical states. In a large time interval, quantum correlations are greater than classical correlations. The quantum and classical correlations can be preserved over a longer period of time via the kernel characterizing the environment memory effects.
In this paper, the dynamics of quantum correlation quantified by local quantum uncertainty (LQU) and local quantum Fisher information (LQFI) for two uncoupled qubits driven by classical phase noisy laser have been investigated. The results show that, both LQU and LQFI exhibit similar behaviours, either display exponential decay or oscillatory decay with revivals depending on the ratios of classical phase noisy laser rate and system-environment coupling strength. Beside, our results also confirm the amount of quantum correlation measured by LQU is strictly bounded by LQFI in an open system. Finally, we propose a scheme to protect quantum correlation against classical phase noisy laser with the technique of weak measurement and reversal.