Towards global time distribution via satellite-based sources of entangled photons br

We propose a satellite-based scheme to perform clock synchronization between ground stations spread acrossthe globe using quantum resources. We refer to this as a quantum clock synchronization (QCS) network. Throughdetailed numerical simulations, we assess the feasibility and capabilities of a near-term implementation of thisscheme. We consider a small constellation of satellites equipped only with modest resources. These include quan-tum devices such as spontaneous parametric down conversion sources, avalanche photodetectors, and moderatelystable on-board clocks such as chip-scale atomic clocks. In our simulations, the various performance parametersdescribing the hardware have been chosen such that they are either already commercially available or requireonly moderate advances. We conclude that with such a scheme, establishing a global network of ground-basedclocks synchronized to subnanosecond level (up to a few picoseconds) of precision would be feasible. SuchQCS satellite constellations would form the infrastructure for a future quantum network, able to serve as aglobally accessible entanglement resource. At the same time, our clock synchronization protocol provides thesubnanosecond level synchronization required for many quantum networking protocols, and thus can be seen asadding an extra layer of utility to quantum technologies in the space domain designed for other purposes