Securing practical quantum communication systems with optical power limiters

TL;DR

This paper introduces a passive thermo-optical power limiter device that enhances security in quantum communication systems by preventing unauthorized light signals without compromising quantum signals, applicable to various quantum cryptography protocols.

Contribution

The paper presents a novel, adjustable, and robust optical power limiter based on thermo-optical effects, specifically designed for secure quantum communication applications.

Findings

The device effectively limits power without affecting quantum signal properties.

It enhances security against Trojan-horse and bright illumination attacks.

Experimental results confirm minimal impact on quantum communication signals.

Abstract

Controlling the energy of unauthorized light signals in a quantum cryptosystem is an essential criterion for implementation security. Here, we propose a passive optical power limiter device based on thermo-optical defocusing effects providing a reliable power limiting threshold which can be readily adjusted to suit various quantum applications. In addition, the device is robust against a wide variety of signal variations (e.g. wavelength, pulse width), which is important for implementation security. Moreover, we experimentally show that the proposed device does not compromise quantum communication signals, in that it has only a very minimal impact (if not, negligible impact) on the intensity, phase, or polarization degrees of freedom of the photon, thus making it suitable for general communication purposes. To show its practical utility for quantum cryptography, we demonstrate and discuss three potential applications: (1) measurement-device-independent quantum key distribution with enhanced security against a general class of Trojan-horse attacks, (2) using the power limiter as a countermeasure against bright illumination attacks, and (3) the application of power limiters to potentially enhance the implementation security of plug-and-play quantum key distribution.