Simple Quantum Key Distribution with qubit-based synchronization and a self-compensating polarization encoder

TL;DR

This paper introduces a simplified, stable, and low-cost quantum key distribution system that uses existing hardware for synchronization and polarization control, achieving high stability and low error rates over fiber-optic links.

Contribution

The work presents a novel QKD system with integrated synchronization and polarization compensation using a self-compensating Sagnac loop, reducing hardware complexity and enhancing stability.

Findings

Operates at 1550 nm with high temporal stability

Tolerates up to 40 dB channel losses in fiber links

Achieves the lowest reported intrinsic quantum bit error rate

Abstract

Quantum Key Distribution (QKD) relies on quantum communication to allow distant parties to share a secure cryptographic key. Widespread adoption of QKD in current telecommunication networks will require the development of simple, low cost and stable systems. However, current QKD implementations usually include additional hardware that perform auxiliary tasks such as temporal synchronization and polarization basis tracking. Here we present a polarization-based QKD system operating at 1550 nm that performs synchronization and polarization compensation by exploiting only the hardware already needed for the quantum communication task. Polarization encoding is performed by a self-compensating Sagnac loop modulator which exhibits high temporal stability and the lowest intrinsic quantum bit error rate reported so far.The QKD system was tested over a fiber-optic link, demonstrating tolerance up to about 40 dB of channel losses. Thanks to its reduced hardware requirements and the quality of the source, this work represents an important step towards technologically mature QKD systems.