Quantumness and the role of locality on quantum correlations

TL;DR

This paper explores how different decompositions of quantum systems can reveal enhanced quantum correlations and introduces a new way to quantify the maximum quantumness of states, challenging traditional measures.

Contribution

It presents a novel approach to defining and quantifying quantum correlations by considering multiple system decompositions and links this to existing correlation criteria.

Findings

Different decompositions reveal varied quantum resources.

New quantification of maximum quantumness of states.

Distinct behaviors for separable and entangled states.

Abstract

Quantum correlations in a physical system are usually studied with respect to a unique (fixed) decomposition of the system into subsystems, without fully exploiting the rich structure of the state-space. Here, we show several examples in which the consideration of different ways to decompose a physical system enhances the quantum resources and accounts for a more flexible definition of quantumness-measures. Furthermore, we give a new perspective regarding how to reassess the fact that local operations play a key role in general quantumness-measures that go beyond entanglement --as discord-like ones. We propose a way to quantify the maximum quantumness of a given state. Applying our definition to low-dimensional bipartite states, we show that different behaviours are reported for separable and entangled states than those corresponding to the usual measures of quantum correlations. We show that there is a close link between our proposal and the criterion to witness quantum correlations based on the rank of the correlation matrix, proposed by Daki\'c, Vedral and Brukner.