# Symmetrical clock synchronization with time-correlated photon pairs

## TL;DR

This paper presents a novel point-to-point clock synchronization protocol using time-correlated photon pairs from SPDC, achieving high precision, security, and suitability for mobile parties, complementing GNSS methods.

## Contribution

The authors introduce a distance-independent, secure clock synchronization protocol based on quantum photon correlations, with potential for authentication and mobile applications.

## Key findings

- Achieved 51 ps synchronization precision in 100 seconds
- Demonstrated security against symmetric delay attacks
- Protocol is compatible with mobile parties and can include authentication

## Abstract

We demonstrate a point-to-point clock synchronization protocol based on bidirectionally exchanging photons produced in spontaneous parametric down conversion (SPDC). The technique exploits tight timing correlations between photon pairs to achieve a precision of 51ps in 100s with count rates of order 200s$^{-1}$. The protocol is distance independent, secure against symmetric delay attacks and provides a natural complement to techniques based on Global Navigation Satellite Systems (GNSS). The protocol works with mobile parties and can be augmented to provide authentication of the timing signal via a Bell inequality check.