  The ability to measure, hold and distribute time with high precision and
accuracy is a foundational capability for scientific exploration. Beyond
fundamental science, time synchronization is an indispensable feature of public
and private communication, navigation and ranging, and distributed sensing,
amongst others technological applications. We propose the implementation of a
quantum network of satellite- and ground-based clocks with the ability to
implement Quantum Clock Synchronization to picosecond accuracy. Implementation
of the proposed QCS network offers a double advantage: (1) a more accurate,
robust, and secure time synchronization network for classical applications than
currently possible, and (2) a resource to fulfill the much more stringent
synchronization requirements of future quantum communication networks.
