Autonomous Picosecond-Precision Synchronization in Measurement-Device-Independent Quantum Key Distribution

TL;DR

This paper introduces an autonomous, high-precision synchronization method for fiber-based MDI-QKD networks that achieves better than 10 ps accuracy over 100 km without auxiliary channels, enhancing network scalability and robustness.

Contribution

A novel synchronization algorithm for MDI-QKD that operates without auxiliary channels or shared clocks, using round-trip pulse propagation and statistical detection.

Findings

Synchronization accuracy better than 10 ps for 100 km channels

Method does not require auxiliary optical channels or shared clocks

Enhances scalability and robustness of quantum networks

Abstract

Measurement-device-independent quantum key distribution (MDI-QKD) eliminates detector side-channel attacks by relocating all measurements to an untrusted intermediate node. However, its practical implementation critically relies on picosecond-level temporal synchronization between spatially separated users. In this work, we present a physically motivated autonomous synchronization algorithm for fiber-based MDI-QKD networks that does not require auxiliary optical channels or shared clock references. The method exploits round-trip optical pulse propagation and statistical signal detection in the presence of Gaussian noise. We derive analytical expressions for false-alarm probabilities, quantify detection reliability, and demonstrate through numerical modeling that synchronization accuracy better than 10~ps is achievable for channel lengths up to 100~km with realistic optical power levels. The proposed approach improves the scalability and robustness of MDI-QKD architectures and is directly applicable to metropolitan and backbone quantum networks.