Quantum time synchronization for real clock networks

Both accurate clocks and synchronization between nodes are necessary to realize the vision of an atomic clock network reaching the frontier in metrology, geodesy, and fundamental physics. Despite great advances in precision... [ view full abstract ]

Both accurate clocks and synchronization between nodes are necessary to realize the vision of an atomic clock network reaching the frontier in metrology, geodesy, and fundamental physics. Despite great advances in precision clocks in recent decades, commonly used time synchronization methods such as GPS and two-way satellite time and frequency transfer (TWSTFT) still lag far behind the accuracy of the best atomic clocks. Quantum time synchronization provides an attractive alternative to using classical timing: the quantum timing signal is far less likely to contaminate the channel link, and provides security against tampering that can otherwise compromise protocols such as key distribution.

In this work, we investigate time synchronization protocols harnessing quantum advantages and discuss their suitability for practical clock networks. In the ideal low-loss, resource-costly regime, we discuss an optimal multipass protocol that reaches the Heisenberg limit and show that its capture time is significantly faster than other classical and quantum protocols under similar conditions. For a real-world, optical fiber-based photonic network, we investigate a more suitable entanglement-based protocol. Using realistic entanglement distribution rates and noise levels of the 43-km Lincoln Laboratory-MIT fiber link, we show that the stability of synchronization can exceed that of state-of-the-art atomic clocks.

Distribution Statement A: Approved for public release: distribution unlimited. This material is based upon work supported by the Assistant Secretary of Defense for Research and Engineering under Air Force Contract No. FA8721-05-C-0002 and/or FA8702-15- D-0001. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Assistant Secretary of Defense for Research and Engineering.