Quantum processes which do not use coherence

Benjamin Yadin, Jiajun Ma, Davide Girolami, Mile Gu, Vlatko Vedral

Published 2015-12-07Version 1

One of the main signatures of quantum mechanics beyond classical physics is coherence, the existence of superposition states. The recently developed resource theory of quantum coherence quantifies this rigorously by supposing a fixed preferred basis for a given physical situation. The incoherent states are identified as mixtures of the preferred basis states, while the incoherent operations are defined such that they cannot create coherence. So far there has been little discussion about the physical meaning of these operations. We show that a subset known as strictly incoherent operations are more relevant to the question of whether a given process makes use of coherence: under strictly incoherent operations, the results of measurements in the preferred basis on the output state do not depend on the coherence of the input state. We demonstrate that measurements in a coherent basis are needed to make use of coherence, and that such measurements must be generated by coherent unitary interactions with an environment. Finally, we show that the strictly incoherent operations provide a natural setting in which to study the behaviour of discord-type quantum correlations, in particular how they may be consumed and generated.