Entropy as a measure of quantum optical correlation

Abstract

Previous work on quantum correlations has focused attention on the influence of the correlation on observables. In this paper we introduce an observable-independent index of correlation based on the information content, or entropy, of that correlation. We analyze a pair of spins and verify that they are maximally correlated when the index of correlation is maximized. The index of correlation suggests that two optical-field modes are most strongly correlated when prepared in a two-mode squeezed state.