Quantum Information as a Measure of Multipartite Correlation

TL;DR

This paper explores using mutual information to measure correlation strength in multipartite quantum systems, revealing that GHZ states uniquely optimize pairwise correlations.

Contribution

It extends the mutual information measure to multipartite systems and identifies GHZ states as optimal for pairwise correlations among qubits.

Findings

Difference between classical and quantum correlation regimes is at most 1 bit.

GHZ states uniquely optimize pairwise correlations in qubit systems.

Correlation content can be expanded into pairwise correlations.

Abstract

The mutual information has been successfully used as a measure of correlation strength between quantum systems, especially for bipartite systems. Here we examine the use of this measure for multipartite quantum systems. For system of qubits we find that the difference between `classical' and `quantum' regimes of correlation strength amounts to just 1 bit of information, at most. We show that the information content of a correlation can be expanded into correlations between pairwise components and demonstrate that in terms of this information-based measure of correlation the GHZ states are the only states that simultaneously optimize these pairwise correlations for systems of qubits.