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Conference on Lasers and Electro-Optics Pacific Rim (CLEO-PR)

Protecting quantum discord using weak measurement and quantum measurement reversal

Jiwon Yune, Kang-Hee Hong, Hyang‐Tag Lim, Jong Chan Lee, Osung Kwon, Sang-Wook Han, Sung Moon, Yong‐Su Kim, Yoon-Ho Kim

Published Aug 1, 2015• 0 citations
Publisher

Abstract

We report that quantum discord can be protected from decoherence by making use of weak and reversing quantum measurements, making it possible to distribute quantum correlation between two remote parties in noisy environment.
DOI
10.1109/cleopr.2015.7376508

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Protection of the quantum coherence and discord in realistic quantum systems interacting with the environment of depolarizing noise is an important subject in quantum information processing. Weak measurement and measurement reversal can effectively suppress the amplitude damping-class decoherence. In this paper, we examine the effect of this protocol in the protection of quantum coherence and discord subjected to depolarizing noise environments. Our scheme consists of a prior weak measurement on each qubit before interacting with noisy channels followed by post measurement reversal. It is found that quantum coherence and discord can be enhanced to an optimal value by performing weak measurements and adjusting measurement parameters on each qubit. In addition, the maximal value of the quantum coherence and discord is found to be independent of the initial-state parameters.
Entanglement is known to be an essential resource for many quantum information processes. However, it is now known that some quantum features may be acheived with quantum discord, a generalized measure of quantum correlation. In this paper, we study how quantum discord, or more specifically, the measures of entropic discord and geometric discord are affected by the influence of amplitude damping decoherence. We also show that a protocol deploying weak measurement and quantum measurement reversal can effectively protect quantum discord from amplitude damping decoherence, enabling to distribute quantum correlation between two remote parties in a noisy environment.
The projective measurement usually destroys the quantum correlation between two subsystems of a composite system, thereby making the measured state useless for any efficient quantum information processing and quantum computation task. The weak measurement acts gently on quantum system and do not force the system state to decohere completely, thus revealing the super quantum discord, which can take value more than that of the normal quantum discord. Remarkably, we prove that the super quantum discord in the post measured state is equal to the difference between the super quantum discord and the normal quantum discord in the original state. Thus, the weak measurement has the ability to resurrect the lost quantumness of any composite quantum state. This suggests a conservation law for the extra quantum correlation in any composite state. The amount of extra quantum correlation which is destroyed by the projective measurement in the original state is equal to the amount of extra quantum correlation captured by the weak measurement in the post-measured state.
Protection of entanglement from disturbance of the environment is an essential task in quantum information processing. We examine the validity and limitation of the weak measurement and reversal (WMR) operation in the protection of distributed entanglement from various decoherence sources. Since the entanglement variation can be investigated analytically for an arbitrarily entangled bipartite pure state under three kinds of typical noisy quantum channels, we show explicitly that the WMR operation indeed helps for protecting distributed entanglement from amplitude damping and phase damping, but not for depolarizing. Experimental feasibility for testing our results is discussed using current laboratory techniques.
We extend the definition of quantum discord as a quantifier of nonClassical correlations in a quantum state to the case where weak measurements are performed on subsystem AAA of a bipartite system ABABAB. The properties of weak discord are explored for several families of quantum states. We find that in many cases weak quantum discord is identical to normal discord and in general the values of the two are very close to each other. Weak quantum discord reduces to discord in the appropriate limits as well. We also discuss the implications of these observations on the interpretations of quantum discord.