Remote quantum clock synchronization without synchronized clocks

TL;DR

This paper demonstrates that entanglement purification can remove unknown phase errors in quantum clock synchronization, enabling synchronization without pre-shared synchronized clocks and outperforming classical methods.

Contribution

It introduces a method to eliminate unknown phase errors in entanglement-based quantum clock synchronization, removing the need for synchronized clocks beforehand.

Findings

The scheme works with noisy Bell pairs and various basis conventions.

It tolerates time offsets and noisy channels.

Performance exceeds classical Einstein synchronization protocols.

Abstract

A major outstanding problem for many quantum clock synchronization protocols is the hidden assumption of the availability of synchronized clocks within the protocol. In general, quantum operations between two parties do not have consistent phase definitions of quantum states, which introduce an unknown systematic phase error. We show that despite prior arguments to the contrary, it is possible to remove this unknown phase via entanglement purification. This closes the loophole for entanglement based quantum clock synchronization protocols, which are most compatible with current photon based long-distance entanglement distribution schemes. Starting with noisy Bell pairs, we show that the scheme produces a singlet state for any combination of (i) differing basis conventions for Alice and Bob; (ii) an overall time offset in the execution of the purification algorithm; and (iii) the presence of a noisy channel. Error estimates reveal that better performance than existing classical Einstein synchronization protocols should be achievable using current technology.