Covariance, correlation and entanglement
R I A Davis, R Delbourgo, P D Jarvis · Journal of Physics A Mathematical and General · 2000
Some new identities for quantum variance and covariance involving commutators are presented, in which the density matrix and the operators are treated symmetrically. A measure of entanglement is proposed for bipartite systems, based upon covariance. This works for two- and three-component systems but produces ambiguities for multicomponent systems of composite dimension. Its relationship to angular momentum dispersion for symmetric spin states is described.