Adaptive versus nonadaptive strategies for quantum channel discrimination

We provide a simple example that illustrates the advantage of adaptive over nonadaptive strategies for quantum channel discrimination. In particular, we give a pair of entanglement-breaking channels that can be perfectly discriminated by means of an adaptive strategy that requires just two channel evaluations, but for which no nonadaptive strategy can give a perfect discrimination using any finite number of channel evaluations.EPSRC of the United Kingdom (Grant “QIP IRC”)xQIT Keck fellowshipCanada Research ChairCanada Foundation for InnovationOntario Research FundCanadian Institute for Advanced ResearchNatural Sciences and Engineering Research Council of CanadaQuantumWork