Poompong Chaiwongkhot

We report recent advances in the development of certification for quantum key distribution (QKD) systems. We give an example of a commercial QKD system that we have analysed for possible loopholes, improved to close the vulnerabilities identified, and designed a set of tests for that can be used by a certification lab [arXiv:2310.20107]. We explain some of the testbenches in this lab, such as an ultrawide spectral characterisation testbench, automated detector testing, and laser damage testbench that verifies the quality of a power limiter. This work is in line with the requirements of the ISO standard for QKD and paves the way for the creation of certification services.

In the age of measurement-device-independent quantum key distribution (MDI QKD) and twin- field QKD (TF QKD), the source units of these QKD schemes may become a new ``Achilles' heel" of the whole system. An adversary, Eve, can conduct various attacks on the sources by injecting lasers, whose power is limited by the laser-induced damage threshold of the quantum channel. Such an amount of power may modify the characteristics of components in a source. In this work, we study possible components to protect the source from the light-injected attacks, i.e., Trojan-horse attack, the laser-seeding attack, and the laser-damage attack. Experimental testing shows that fiber-optics isolators and circulators are good passive countermeasures because they sacrifice themselves' isolation under a high-power laser to protect other components behind them. Moreover, we find that illuminated by the high-power laser, integrated photonics QKD chips only lose the transmission of the coupler before any other change happens for the other components in the chips.