  Recently some authors have pointed out that there exist nonclassical
correlations which are more general, and possibly more fundamental, than
entanglement. For these general quantum correlations and their classical
counterparts, under the action of decoherence, we identify three general types
of dynamics that include a peculiar sudden change in their decay rates. We show
that, under suitable conditions, the classical correlation is unaffected by
decoherence. Such dynamic behavior suggests an operational measure of both
classical and quantum correlations that can be computed without any
extremization procedure.
