Displacement receiver for phase-shift-keyed coherent states

TL;DR

This paper proposes a practical quantum receiver design for discriminating phase-shifted coherent states, demonstrating improved error rates over classical limits without requiring complex feedforward for ternary signals.

Contribution

It introduces a feedforward-free quantum receiver for ternary states and analyzes the importance of feedforward in quaternary state discrimination.

Findings

Ternary signals achieve error rate improvement over SQL without feedforward.

Feedforward is essential for quaternary signals to surpass SQL with imperfect devices.

Analytical results on asymptotic performance with increasing feedforward steps.

Abstract

Quantum receiver is an important tool for overcoming the standard quantum limit (SQL) of discrimination errors in optical communication. We theoretically study the quantum receivers for discriminating ternary and quaternary phase shift keyed coherent states in terms of average error rate and mutual information. Our receiver consists of on/off-type photon detectors and displacement operations w/o electrical feedforward operations. We show that for the ternary signals, the receiver shows a reasonable gain from the SQL even without feedforward. This scheme is realizable with the currently available technology. For the quaternary signals feedforward operation is crucial to overcome the SQL with imperfect devices. We also analytically examine the asymptotic limit of the performance of the proposed receiver with respect to the number of feedforward steps.