On Covert Quantum Sensing and the Benefits of Entanglement

TL;DR

This paper investigates covert quantum sensing, demonstrating how entanglement can enhance undetectable parameter estimation in quantum channels, with practical implications for quantum radar and security.

Contribution

It characterizes the optimal error exponent under covertness constraints and shows how entanglement improves covert sensing when using unitary channels.

Findings

Optimal error exponent characterized for classical-quantum channels

Entanglement significantly improves covertness in unitary channel sensing

Achievability and converse results demonstrate benefits of entangled inputs

Abstract

Motivated by applications to covert quantum radar, we analyze a covert quantum sensing problem, in which a legitimate user aims at estimating an unknown parameter taking finitely many values by probing a quantum channel while remaining undetectable from an adversary receiving the probing signals through another quantum channel. When channels are classical-quantum, we characterize the optimal error exponent under a covertness constraint for sensing strategies in which probing signals do not depend on past observations. When the legitimate user's channel is a unitary depending on the unknown parameter, we provide achievability and converse results that show how one can significantly improve covertness using an entangled input state.