Clocks Beyond Classical Space-Time

Ronakraj Gosalia, Ryan Aguinaldo, Jonathan Tyler Green +3 more

The next generation of space-based networks for communications, sensing, and navigation will contain optical clocks embedded within satellites. To fully realize the capabilities of such clocks, high-precision clock synchronization across the networks will be necessary. Current experiments have shown the potential for classical frequency combs to synchronize remote optical clocks over free space. However, these classical combs are restricted in precision to the standard quantum limit. Quantum frequency combs, however, which exhibit quantum properties such as squeezing and entanglement, provide pathways for going beyond the standard quantum limit. Here, we present our perspective on the prospects for practical clock synchronization in space using both classical and quantum frequency combs. We detail the current outcomes achievable with a classical frequency comb approach to synchronization, before quantifying the potential outcomes offered by quantum frequency combs. Challenges to be overcome in deploying frequency combs in space are presented, and the implications of almost-perfect synchronization for future space-based applications and experiments are discussed.

David Finkelstein

K. L. H. Bryan, A. J. M. Medved

James E. Troupe, Stav Haldar, Iván Agulló +1 more

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.

Maxim Khodas, Tuvia Gefen, Liam Paul McGuinness +2 more

Quantum spectroscopy with single qubits has improved considerably our ability to detect weak signals arising from classical and quantum sources. Recently, the use of additional memory qubits in quantum spectroscopy has allowed a resolution beyond the sensor coherence time to be reached. Alternatively, combining a classical clock allows for spectroscopy of classical fields with a resolution given by the clock coherence time. We present a novel correlation spectroscopy technique with resolution that is limited by the coherence time of the classical clock. This method is capable of screening the classical signal while still being able to detect the quantum one.

Maximilian P. E. Lock, Ivette Fuentes