Achievability of Covert Quantum Communication

TL;DR

This paper demonstrates that it is possible to covertly transmit a number of qubits proportional to the square root of the number of channel uses over quantum channels, ensuring undetectability from adversaries.

Contribution

It establishes the quantum analog of the classical square root law for covert communication over arbitrary quantum channels, including scenarios with and without classical assistance.

Findings

Achievability of the square root law for quantum covert communication.

Quantification of classical covert bits needed for protocols.

Lower bounds on the number of qubits transmitted covertly.

Abstract

We explore covert communication of qubits over an arbitrary quantum channel. Covert communication conceals the transmissions in the channel noise, ensuring that an adversary is unable to detect their presence. We show the achievability of a $\textit{square root law}$ (SRL) for quantum covert communication similar to that for classical: $M(n)\propto\sqrt{n}$ qubits can be transmitted covertly and reliably over $n$ uses of a general quantum channel. We lower bound $M(n)$ with and without assistance from a two-way covert classical channel. In the former case, we quantify the number of classical covert bits sufficient for our protocol.