LAUSR

Quantum feedback control (QFBC) and quantum feedforward control (QFFC) are two major techniques for protecting quantum states against decoherence. Based on this, Guo et al. proposed a scheme by combining the QFFC and the minimum-error discrimination (MED) to realize a better effect of discriminating two non-orthogonal states after passing a noisy channel (Phys Rev A 91:022321, 2015) than the scheme without the QFFC. Recently, Cao et al. proposed a novel composite control scheme for protecting such states (Phys Rev A 95:032313, 2017), where QFBC and QFFC are combined. They showed that the performance of the composite control scheme is better than that of the previous control schemes in terms of the success probability and the fidelity. In this paper, we examine the discrimination scheme by combining the composite control and the MED and observe an interesting phenomenon, i.e., better quantum control does not imply better discrimination effect. Finally, we explain this phenomenon.