Quantum hacking: Experimental demonstration of time-shift attack against practical quantum-key-distribution systems

TLDR

Quantum‑key‑distribution systems can transmit quantum signals over more than 100 km of standard optical fiber and are widely believed to be secure. The study experimentally demonstrates a technologically feasible time‑shift attack against a commercial QKD system. The attack exploits the detection‑efficiency loophole by shifting photon arrival times to manipulate detector responses. The experiment shows that Eve can break the system’s security with a ~4 % success probability, confirming that the detection‑efficiency loophole is a critical vulnerability in both fundamental physics tests and practical QKD applications.

Abstract

Quantum-key-distribution (QKD) systems can send quantum signals over more than $100\phantom{\rule{0.3em}{0ex}}\mathrm{km}$ standard optical fiber and are widely believed to be secure. Here, we show experimentally a technologically feasible attack---namely, the time-shift attack---against a commercial QKD system. Our result shows that, contrary to popular belief, an eavesdropper, Eve, has a non-negligible probability $(\ensuremath{\sim}4%)$ to break the security of the system. Eve's success is due to the well-known detection efficiency loophole in the experimental testing of Bell's inequalities. Therefore, the detection efficiency loophole plays a key role not only in fundamental physics, but also in technological applications such as QKD systems.