  This paper introduces coherent quantum channel discrimination as a coherent
version of conventional quantum channel discrimination. Coherent channel
discrimination is phrased here as a quantum interactive proof system between a
verifier and a prover, wherein the goal of the prover is to distinguish two
channels called in superposition in order to distill a Bell state at the end.
The key measure considered here is the success probability of distilling a Bell
state, and I prove that this success probability does not increase under the
action of a quantum superchannel, thus establishing this measure as a
fundamental measure of channel distinguishability. Also, I establish some
bounds on this success probability in terms of the success probability of
conventional channel discrimination. Finally, I provide an explicit
semi-definite program that can compute the success probability.
