Characterizing Nonclassical Correlations via Local Quantum Uncertainty

TL;DR

This paper introduces a measure of nonclassical correlations based on local quantum uncertainty, demonstrating its role in guaranteeing minimum precision in quantum metrology, especially in phase estimation tasks.

Contribution

It defines a unique measure of nonclassical correlations for 2 x d systems using local quantum uncertainty and explores its implications for quantum metrology.

Findings

A unique measure of nonclassical correlations is derived for 2 x d systems.

The measure is evaluated in closed form for specific bipartite systems.

Quantum discord in bipartite states guarantees a minimum precision in phase estimation.

Abstract

Quantum mechanics predicts that measurements of incompatible observables carry a minimum uncertainty which is independent of technical deficiencies of the measurement apparatus or incomplete knowledge of the state of the system. Nothing yet seems to prevent a single physical quantity, such as one spin component, from being measured with arbitrary precision. Here we show that an intrinsic quantum uncertainty on a single observable is ineludible in a number of physical situations. When revealed on local observables of a bipartite system, such uncertainty defines an entire class of bona fide measures of nonclassical correlations. For the case of 2 x d systems, we find that a unique measure is defined, which we evaluate in closed form. We then discuss the role that these correlations, which are of the 'discord' type, can play in the context of quantum metrology. We show in particular that the amount of discord present in a bipartite mixed probe state guarantees a minimum precision, as quantified by the quantum Fisher information, in the optimal phase estimation protocol.