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A Quantum Network of Clocks
The development of precise atomic clocks has led to many scientific and technological advances that play an increasingly important role in modern society. Shared timing information constitutes a key resource for positioning and navigation with a direct correspondence between timing accuracy and precision in applications such as the Global Positioning System (GPS). By combining precision metrology and quantum networks, we proposed a quantum, cooperative protocol for the operation of a network consisting of geographically remote optical atomic clocks. Through use of non-local entangled states, we demonstrated an optimal utilization of the global network resources, and showed that such a network could be operated near the fundamental limit set by quantum theory that yielded an ultra-precise clock signal. Furthermore, the internal structure of the network, combined with basic techniques from quantum communication, guaranteed security both from internal and external threats. Realization of such a global quantum network of clocks may allow construction of a real-time single international time scale (world clock) with unprecedented stability and accuracy.