Quantum Limits to Classically Spoofing an Electromagnetic Signal

TL;DR

This paper investigates the fundamental quantum limits on classical spoofing of electromagnetic signals, demonstrating that quantum mechanics imposes significant restrictions on the ability to successfully spoof signals even with high photon numbers.

Contribution

The study introduces an idealized quantum spoofing model using non-orthogonal coherent states and shows that quantum-mechanical constraints prevent perfect spoofing, enabling detection and discrimination.

Findings

Quantum spoofing strategies are limited by quantum mechanics.

Imperfect spoofs can be detected or distinguished from true signals.

Quantum limitations persist even at high photon numbers.

Abstract

Spoofing an electromagnetic signal involves measuring its properties and preparing a spoof signal that is a close enough copy to fool a receiver. A classic application of spoofing is in radar where an airborne target attempts to avoid being tracked by a ground-based radar by emitting pulses indicating a false range or velocity. In certain scenarios it has been shown that a sensor can exploit quantum mechanics to detect spoofing at the single-photon level. Here we analyze an idealized spoofing scenario where a transmitter-receiver pair, seeking to detect spoofing, utilizes a signal chosen randomly from a set of non-orthogonal, coherent states. We show that a spoofer optimally employing classical information on the state of the transmitted signal (i.e. the best measure-and-prepare strategy allowed by quantum mechanics) inevitably emits imperfect spoofs that can be exploited by the receiver to reveal the presence of the spoofer, or to discriminate between true reflections and spoofs. Importantly, we show that the quantum limitations on classical spoofing remain significant even in the large mean-photon-number regime.