Quantum information as a measure of multipartite correlation

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 optimise these pairwise correlations for systems of qubits.