  Unambiguous discrimination and exact cloning reduce the square-overlap
between quantum states, exemplifying the more general type of procedure we term
state separation. We obtain the maximum probability with which two equiprobable
quantum states can be separated by an arbitrary degree, and find that the
established bounds on the success probabilities for discrimination and cloning
are special cases of this general bound. The latter also gives the maximum
probability of successfully producing N exact copies of a quantum system whose
state is chosen secretly from a known pair, given M initial realisations of the
state, where N>M. We also discuss the relationship between this bound and that
on unambiguous state discrimination.
