Adaptive generalized measurement for unambiguous state discrimination of quaternary phase-shift-keying coherent states

TL;DR

This paper demonstrates an adaptive measurement scheme that unambiguously discriminates quaternary phase-shift-keying coherent states with near-optimal performance, improving success rates over traditional static methods.

Contribution

The authors experimentally implement an adaptive generalized measurement scheme that enhances unambiguous state discrimination of coherent states compared to conventional static approaches.

Findings

Improved probability of conclusive results.

Reduced erroneous decision ratio.

Near-optimal discrimination performance.

Abstract

Generalized quantum measurements identifying non-orthogonal states without ambiguity often play an indispensable role in various quantum applications. For such unambiguous state discrimination scenario, we have a finite probability of obtaining inconclusive results and minimizing the probability of inconclusive results is of particular importance. In this paper, we experimentally demonstrate an adaptive generalized measurement that can unambiguously discriminate the quaternary phase-shift-keying coherent states with a near-optimal performance. Our scheme is composed of displacement operations, single photon detections and adaptive control of the displacements dependent on a history of photon detection outcomes. Our experimental results show a clear improvement of both a probability of conclusive results and a ratio of erroneous decision caused by unavoidable experimental imperfections over conventional static generalized measurements.