Keyless Covert Communication Over Quantum MACs with General Message Sets

2026-07-09

AI Summary

This study addresses the achievability of positive-rate keyless covert communication over quantum multiple-access channels (MACs) for arbitrary message sets. Leveraging quantum information theory, the framework of covert communication analysis, and information-spectrum methods, the work establishes—under deterministic encoding constraints—the first finite-blocklength and asymptotic achievable covert rate regions for classical–quantum MACs, thereby characterizing their covert capacity. The results unify and generalize existing findings, encompassing canonical scenarios such as finite-dimensional, Gaussian, and single-mode bosonic MACs. Notably, this is the first demonstration that positive covert communication rates are attainable in multi-user quantum MACs without requiring shared secret keys.

Abstract

We study covert classical communication over quantum multiple-access channels (MACs) with general message sets. Specifically, we consider a fully quantum MAC with arbitrary message sets and an arbitrary number of transmitters. We demonstrate the feasibility of achieving a positive covert rate over this channel and establish general one-shot and asymptotic achievable rate regions. For classical-quantum MACs with general message sets, we establish the covert capacity, when the transmitters are restricted to deterministic encoding. Our result recovers, as a special case, known results for classical communication over classical MACs with general message sets, covert communication of a classical message over a classical channel with two transmitters, and classical communication over quantum MACs. We provide three examples of MACs to which our results can be applied, either directly or indirectly, to achieve positive covert rates. Specifically, we first study covert communication over a finite-dimensional MAC with a helper. We then analyze a classical Gaussian MAC with a helper and derive its covert capacity. Finally, we extend the analysis to a single-mode bosonic MAC with a helper and show that positive covert rates can also be achieved in this setting. To the best of our knowledge, this is the first work to achieve positive-rate covert communication over both classical and quantum MACs.

Problem

• covert communication
• quantum MACs
• general message sets
• positive covert rate

Innovation

• covert communication
• quantum multiple-access channel
• covert capacity
• general message sets
• deterministic encoding