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Journal of Physics B Atomic Molecular and Optical Physics

Controlling sudden transitions of bipartite quantum correlations under dephasing via dynamical decoupling

Jian-Song Zhang, Aixi Chen

Published Oct 15, 2014• 10 citations
Publisher

Abstract

Sudden transitions of one-norm geometric quantum discord and quantum discord of quantum systems have been observed in experiments recently. We propose a scheme to control sudden transitions of quantum correlations of two qubits within two spatially separated thermal baths or one common thermal bath via bang-bang pulses with a finite period. For the two-bath case, correlations decrease with time, and the sudden transition behavior can be efficiently adjusted by bang-bang pulses. For one common bath case, the thermal bath may play a constructive or destructive role in the generation of steady-state correlations, depending on the initial state of qubits.

DOI
10.1088/0953-4075/47/21/215502

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Sudden transitions of one-norm geometric quantum discord and quantum discord of quantum systems have been observed in experiments recently. We propose a scheme to control sudden transitions of quantum correlations of two qubits within two spatially separated thermal baths or one common thermal bath via bang-bang pulses with a finite period. For the two-bath case, correlations decrease with time, and the sudden transition behavior can be efficiently adjusted by bang-bang pulses. For one common bath case, the thermal bath may play a constructive or destructive role in the generation of steady-state correlations, depending on the initial state of qubits.
We study the dynamics of two initially correlated qubits coupled to their own separate spin baths modeled by an XYXYXY spin chain and find the explicit expression of the quantum discord for the system. A sudden transition is found to exist between classical and quantum decoherence by choosing certain initial states. We show that the sudden transition happens near the critical point, which provides an alternative way to characterize the quantum phase transition. Furthermore, we propose a scheme to prolong the transition time of the quantum discord by applying the bang-bang pulses.
We investigate the phenomenon of sudden transitions in geometric quantum correlation of two qubits in spin chain environments at finite temperature. It is shown that when only one qubit is coupled to the spin environment, the geometric discord exhibits a double sudden transition behavior, which is closely related to the quantum criticality of the spin chain environment. When two qubits are uniformly coupled to a common spin chain environment, the geometric discord is found to display a sudden transition behavior whereby the system transits from pure classical decoherence to pure quantum decoherence. Moreover, an interesting scaling behavior is revealed for the frozen time, and we also present a scheme to prolong the time during which the discord remains constant by applying bang–bang pulses.
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.
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