Near-optimal coherent state discrimination via continuously labelled non-Gaussian measurements

Key findings from this study

• The study demonstrates that continuously labelled non-Gaussian measurements can surpass the Gaussian limit and achieve error rates approaching the Helstrom bound for coherent state discrimination.
• The authors report that non-Gaussian unitary operations combined with homodyne detection and orthogonal polynomial protocols both enable near-optimal discrimination without photon detection.
• The researchers find that the proposed schemes maintain performance advantages over the Kennedy receiver across moderate coherent state amplitudes.

Overview

Quantum state discrimination via coherent state analysis remains essential for quantum information and communication systems. Existing measurement approaches include photon detection, which yields discrete outcomes and can approach theoretical optimality, and homodyne detection, which yields continuous outcomes but suffers from higher error rates bounded by the Gaussian limit. This study establishes that continuously labelled non-Gaussian measurements can achieve near-optimal coherent state discrimination despite fundamental operational differences from discrete measurement schemes.

Methods and approach

The researchers designed two discrimination protocols employing continuously labelled non-Gaussian measurements. The first protocol integrates non-Gaussian unitary operations with homodyne detection. The second protocol leverages orthogonal polynomials as a measurement framework. Both approaches operate within the continuous-outcome measurement paradigm while circumventing conventional Gaussian measurement constraints.

Results

Both protocols surpass the Gaussian limit for coherent state discrimination error rates. The non-Gaussian schemes achieve error rates approaching the Helstrom bound across low-energy regimes. At moderate coherent state amplitudes, the proposed continuously labelled protocols maintain performance advantages over the Kennedy receiver, a standard photon detection-based discrimination method. Near-optimal discrimination emerges feasible without discrete photon detection measurements.

Implications

This work challenges the implicit hierarchy suggesting photon detection uniquely enables near-optimal coherent state discrimination. Continuous measurement frameworks, when augmented with non-Gaussian operations or polynomial-based approaches, prove capable of approaching fundamental performance limits. The findings expand the experimental toolkit for quantum state discrimination by validating alternative measurement modalities with comparable efficacy to discrete detection schemes.

Practical implications extend to quantum communication systems where homodyne detection infrastructure dominates over single-photon detection. Implementing non-Gaussian operations or polynomial measurement bases on existing homodyne platforms could enhance discrimination fidelity without requiring substantial apparatus modifications. The moderate-amplitude regime performance advantage suggests applicability in quantum key distribution and related protocols operating within typical coherent state intensity ranges.

Scope and limitations

This summary is based on the study abstract and available metadata. It does not include a full analysis of the complete paper, supplementary materials, or underlying datasets unless explicitly stated. Findings should be interpreted in the context of the original publication.