title: Interference of quantum channels.
abstract: We show how interferometry can be used to characterize certain aspects of general quantum processes and, in particular, the coherence of completely positive maps. We derive a measure of coherent fidelity, the maximum interference visibility, and the closest unitary operator to a given physical process under this measure.
authors.affiliation: Centre for Quantum Computation, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom. D.K.L.Oi@damtp.cam.ac.uk
authors.forename: Daniel K L
authors.initials: DK
authors.lastname: Oi