Linear optics and photodetection achieve near-optimal unambiguous coherent state discrimination

TL;DR

This paper develops a practical theory for unambiguous discrimination of coherent states using linear optics and photon detection, showing near-optimal performance with existing optical components.

Contribution

It introduces a realistic receiver model for USD of coherent states employing passive linear optics, displacements, vacuum modes, and on-off detection, bridging theory and practical implementation.

Findings

Current optical components can achieve near-optimal USD performance.

The proposed receiver design is feasible with existing technology.

Regimes where near-optimal discrimination is achievable are identified.

Abstract

Coherent states of the quantum electromagnetic field, the quantum description of ideal laser light, are prime candidates as information carriers for optical communications. A large body of literature exists on their quantum-limited estimation and discrimination. However, very little is known about the practical realizations of receivers for unambiguous state discrimination (USD) of coherent states. Here we fill this gap and outline a theory of USD with receivers that are allowed to employ: passive multimode linear optics, phase-space displacements, auxiliary vacuum modes, and on-off photon detection. Our results indicate that, in some regimes, these currently-available optical components are typically sufficient to achieve near-optimal unambiguous discrimination of multiple, multimode coherent states.