Idler-Free Multi-Channel Discrimination via Multipartite Probe States

TL;DR

This paper develops and analyzes unassisted, multipartite quantum protocols for multi-channel discrimination, demonstrating quantum advantages in bosonic loss and noise detection without the need for entangled idler modes, thus simplifying practical quantum sensing.

Contribution

It introduces a general framework for idler-free multi-channel discrimination protocols and shows their effectiveness in bosonic channel discrimination tasks.

Findings

Idler-free protocols can outperform classical strategies in bosonic loss discrimination.

Quantum advantage is achievable without entangled idler modes in certain scenarios.

The framework broadens practical quantum sensing applications by reducing resource requirements.

Abstract

The characterisation of Quantum Channel Discrimination (QCD) offers critical insight for future quantum technologies in quantum metrology, sensing and communications. The task of multi-channel discrimination creates a scenario in which the discrimination of multiple quantum channels can be equated to the idea of pattern recognition, highly relevant to the tasks of quantum reading, illumination and more. Whilst the optimal quantum strategy for many scenarios is an entangled idler-assisted protocol, the extension to a multi-hypothesis setting invites the exploration of discrimination strategies based on unassisted, multipartite probe states. In this work, we expand the space of possible quantum enhanced protocols by formulating general classes of unassisted multi-channel discrimination protocols which are not assisted by idler modes. Developing a general framework for idler-free protocols, we perform an explicit investigation in the bosonic setting, studying prominent Gaussian channel discrimination problems for real world applications. Our findings uncover the existence of strongly quantum advantageous, idler-free protocols for the discrimination of bosonic loss and environmental noise. This circumvents the necessity for idler assistance to achieve quantum advantage in some of the most relevant discrimination settings, significantly loosening practical requirements for prominent quantum sensing applications.