A robust quantum receiver for phase shift keyed signals

TL;DR

This paper introduces a robust quantum receiver that uses feedback and photon counting to discriminate phase-shifted signals more effectively than classical methods, approaching the theoretical quantum limit.

Contribution

It presents an optimized quantum receiver design that surpasses the standard quantum limit and remains robust under realistic noise and imperfections.

Findings

Outperforms the standard quantum limit in signal discrimination

Approaches the Helstrom bound for various signal powers

Remains effective under realistic noise conditions

Abstract

The impossibility of perfectly discriminating non orthogonal quantum states imposes far-reaching consequences both on quantum and classical communication schemes. We propose and numerically analyze an optimized quantum receiver for the discrimination of phase encoded signals. Our scheme outperforms the standard quantum limit and approaches the Helstrom bound for any signal power. The discrimination is performed via an optimized, feedback-mediated displacement prior to a photon counting detector. We provide a detailed analysis of the influence of excess noise and technical imperfections on the average error probability. The results demonstrate the receiver's robustness and show that it can outperform any classical receiver over a wide range of realistic parameters.