  We show that there exist bipartite quantum states which contain large hidden
classical correlation that can be unlocked by a disproportionately small amount
of classical communication. In particular, there are $(2n+1)$-qubit states for
which a one bit message doubles the optimal classical mutual information
between measurement results on the subsystems, from $n/2$ bits to $n$ bits.
States exhibiting this behavior need not be entangled. We study the range of
states exhibiting this phenomenon and bound its magnitude.
