Multi-state discrimination below the quantum noise limit at the single-photon level

TL;DR

This paper demonstrates a method to discriminate multiple coherent light states at the single-photon level with sensitivities surpassing the quantum noise limit, using adaptive measurements with practical detection techniques.

Contribution

It introduces a theoretically and experimentally validated strategy for multi-state discrimination that exceeds the quantum noise limit under realistic conditions.

Findings

Achieved discrimination sensitivities below the quantum noise limit at the single-photon level.

Demonstrated robustness of the method with photon number resolving detection.

Applicable across a range of input powers, surpassing the QNL under realistic conditions.

Abstract

Measurements approaching the ultimate quantum limits of sensitivity are central in quantum information processing, quantum metrology, and communication. Quantum measurements to discriminate multiple states at the single-photon level are essential for optimizing information transfer in low-power optical communications and quantum communications, and can enhance the capabilities of many quantum information protocols. Here, we theoretically investigate and experimentally demonstrate the discrimination of multiple coherent states of light with sensitivities surpassing the quantum noise limit (QNL) at the single-photon level under realistic conditions of loss and noise based on strategies implementing globally-optimized adaptive measurements with single photon counting and displacement operations. These discrimination strategies can provide realistic advantages to enhance information transfer at low powers, and are compatible with photon number resolving detection, which provides robustness at high powers, thus allowing for surpassing the QNL at arbitrary input power levels under realistic conditions.