Incompatibility of quantum channels

Abstract

Two quantum channels are called compatible if they can be obtained as\nmarginals from a single broadcasting channel; otherwise they are incompatible.\nWe derive a characterization of the compatibility relation in terms of\nconcatenation and conjugation, and we show that all pairs of sufficiently noisy\nquantum channels are compatible. The complement relation of incompatibility can\nbe seen as a unifying aspect for many quantum features. We demonstrate that\nseveral phenomena, such as impossibility of universal broadcasting and\nunavoidable measurement disturbance, appear naturally in this framework.\n