Experimental secure quantum key distribution in presence of polarization-dependent loss

TL;DR

This paper experimentally investigates polarization-dependent loss in practical QKD devices, demonstrating its impact on security and key rate estimation, and reports a secure decoy-state BB84 QKD implementation over 75 km fiber considering realistic device flaws.

Contribution

It provides the first experimental characterization of polarization-dependent loss in realistic QKD devices and incorporates this into a finite-key security analysis for practical fiber links.

Findings

Significant polarization-dependent loss found in fiber- and silicon-based modulators.

Overestimation of secure key rate occurs if polarization-dependent loss is ignored.

Achieved secure QKD over 75 km fiber considering realistic device imperfections.

Abstract

Quantum key distribution (QKD) is theoretically secure using the principle of quantum mechanics; therefore, QKD is a promising solution for the future of secure communication. Although several experimental demonstrations of QKD have been reported, they have not considered the polarization-dependent loss in state preparation in the key-rate estimation. In this study, we experimentally characterized polarization-dependent loss in realistic state-preparation devices and verified that a considerable PDL exists in fiber- and silicon-based polarization modulators. Hence, the security of such QKD systems is compromised because of the secure key rate overestimation. Furthermore, we report a decoy-state BB84 QKD experiment considering polarization-dependent loss. Finally, we achieved rigorous finite-key security bound over up to 75 km fiber links by applying a recently proposed security proof. This study considers more realistic source flaws than most previous experiments; thus, it is crucial toward a secure QKD with imperfect practical devices.