Detecting quantum correlations in separable systems

TL;DR

This paper develops conditions and methods for detecting quantum correlations, specifically quantum discord, in separable systems using witness operators, facilitating experimental detection beyond entanglement.

Contribution

It introduces necessary and sufficient conditions for hermitian witness operators for quantum discord and proposes a practical linear witness for experimental detection.

Findings

Derived conditions for hermitian witnesses detecting quantum discord

Proposed a linear witness applicable to large classes of separable systems

Showed decomposition of witnesses into measurable local operators

Abstract

Quantum correlations in composite and separable quantum systems are characterized by non-vanishing quantum discord. We demonstrate the necessary and sufficient conditions for existence of hermitian witness operators for quantum discord, bypassing the problem of non-convexity of the set of all classical states. We propose an example of a linear witness which can detect quantum correlations in large classes of separable bipartite systems. Decomposition of the witness in terms of a small number of locally measurable operators as shown here, paves the way for experimental detection of quantum correlations beyond entanglement.