Discriminating two non-orthogonal states against decoherence by feedback control

Abstract

Guo et al. (Phys Rev A 91(2):022321, 2015) introduced the feed-forward control to realize a better effect of discrimination of two non-orthogonal states against noise. However, the better effect of discrimination is achieved in a probabilistic way. To solve the problem, we introduce the feedback control to discriminate two non-orthogonal states against noise. It is shown that it can improve the effect of discrimination for any pair of non-orthogonal states and any strength of amplitude damping noise largely in a deterministic way. In particular, our optimum probability of discrimination can be higher than that of discriminating two initial non-orthogonal pure states for not only equal a priori probabilities but also unequal a priori probabilities. We also examine the approach in the presence of different noise sources and find it works well for all typical types of noise sources ranging from a single type of noise to the combination of different types of noise.