  When a quantum system is divided into two local subsystems, measurements on
the two subsystems can exhibit correlations beyond those possible in a
classical joint probability distribution; these are partially explained by
entanglement, and more generally by a wider class of measures such as the
quantum discord. In this work, I introduce a simple thought experiment defining
a new measure of quantum correlations, which I call the accord, and write the
result as a minimax optimization over unitary matrices. I find the exact result
for pure states as a simple function of the Schmidt coefficients and provide a
complete proof, and I likewise provide and prove the result for several classes
of mixed states, notably including all states of two qubits and the
experimentally relevant case of a pure state mixed with colorless noise. I
demonstrate that for two qubit states the accord provides a tight lower bound
on the discord; for Bell diagonal states it is also an upper bound on
entanglement.
