Super Quantum Discord with Weak Measurements

TL;DR

This paper introduces the concept of super quantum discord, showing that weak measurements can reveal greater quantum correlations than strong measurements, and explores how measurement strength influences quantum discord.

Contribution

It proves that super quantum discord exceeds normal quantum discord and demonstrates its monotonicity with measurement strength, revealing new aspects of quantum correlations.

Findings

Super quantum discord is always larger than quantum discord from strong measurements.

Super quantum discord can surpass quantum entanglement in pure states.

Super quantum discord depends on measurement strength and can be increased with weaker measurements.

Abstract

Weak measurements cause small change to quantum states, thereby opening up the possibility of new ways of manipulating and controlling quantum systems. We ask, can weak measurements reveal more quantum correlation in a composite quantum state? We prove that the weak measurement induced quantum discord, called as the "super quantum discord", is always larger than the quantum discord captured by the strong measurement. Moreover, we prove the monotonicity of the super quantum discord as a function of the measurement strength. We find that unlike the normal quantum discord, for pure entangled states, the super quantum discord can exceed the quantum entanglement. Our result shows that the notion of quantum correlation is not only observer dependent but also depends on how weakly one perturbs the composite system.