A quantum-assisted master clock in the sky: global synchronization from satellites at sub-nanosecond precision

This article develops a protocol to synchronize clocks on board a network of satellites equipped with quantum resources. We show that, in such a constellation, satellites reinforce each other's sync capabilities, forming a common clock that is more stable and precise than its constituents. We envision the resulting network as a master clock able to distribute time across the globe, providing the basis for a future quantum global navigation satellite system or a space-based quantum network. As an example of its capabilities, we show that a constellation of 50 satellites equipped with modest quantum resources, and distributed amongst 5 orbits at an altitude of 500 km, allows the synchronization of clocks spread across the globe at sub-nanosecond precision.