  We propose an information-theoretic quantifier for the advantage gained from
cooperation that captures the degree of dependency between subsystems of a
global system. The quantifier is distinct from measures of multipartite
correlations despite sharing many properties with them. It is directly
computable for classical as well as quantum systems and reduces to comparing
the respective conditional mutual information between any two subsystems.
Exemplarily we show the benefits of using the new quantifier for symmetric
quantum secret sharing. We also prove an inequality characterizing the lack of
monotonicity of conditional mutual information under local operations and
provide intuitive understanding for it. This underlines the distinction between
the multipartite dependence measure introduced here and multipartite
correlations.

Quantum Physics