Cascaded quantum time transfer breaking the no-cloning barrier with entanglement relay architecture

TL;DR

This paper introduces a cascaded quantum time transfer method using entanglement relays, overcoming the no-cloning barrier, and demonstrates sub-picosecond stability over 200 km fiber links with experimental validation.

Contribution

It proposes a novel cascaded architecture for quantum time transfer that maintains high stability over long distances, surpassing previous no-cloning limitations.

Findings

Achieved 3.82 ps stability at 10 s and 0.39 ps at 5120 s over 200 km

Experimental results agree with theoretical models of sublinear stability growth

Demonstrated preservation of quantum timing stability across multiple relay stations

Abstract

Quantum two-way time transfer (Q-TWTT) leveraging energy-time entangled biphotons has achieved sub-picosecond stability but faces fundamental distance limitations due to the no-cloning theorem's restriction on quantum amplification. To overcome this challenge, we propose a cascaded Q-TWTT architecture employing relay stations that generate and distribute new energy-time entangled biphotons after each transmission segment. Theoretical modeling reveals sublinear standard deviation growth (merely N increase for N equidistant segments), enabling preservation of sub-picosecond stability over extended distances. We experimentally validate this approach using a three-station cascaded configuration over 200 km fiber segments, demonstrating strong agreement with theory. Utilizing independent Rb clocks at end and relay stations with online frequency skew correction, we achieve time stabilities of 3.82 ps at 10 s and 0.39 ps at 5120 s. The consistency in long-term stability between cascaded and single-segment configurations confirms high-precision preservation across modular quantum networks. This work establishes a framework for long-distance quantum time transfer that surpasses the no-cloning barrier, providing a foundation for future quantum-network timing infrastructure.