Synchronization of FNAL and ANL for quantum communications

We distribute clock synchronization on a three-node quantum network between Fermi and Argonne National Laboratories, connected via 59km of optical fiber. Quantum photon pairs are generated at the telecommunications C-band whereas the classical optical clock signal is generated in the O- and L-bands and coexists with the quantum photons in the fiber. The photon pairs and clock signals are directed to nodes through a standard telecommunication switch, with the clock signals providing picosecond-scale timing resolution to synchronize the photon pairs. We study the properties of the Raman scattering for the clock signal in the optical fiber used in the network, determining that we have a Raman scattering coefficient of 20.8 ± 0.3 x 10-10 for the L-band and 4.6 ± 0.1 x 10-10 for the O-band. We measure the coincidence-to-accidental ratio (CAR) of the photon pairs with and without the coexisting clock signal to determine the amount of Raman scattering occurring from the clock signal into the quantum frequency channel. We notice a reduction in the CAR from 51 ± 2 to 5.3 ± 0.4 when the quantum light coexists with the O-band clock pulses. Even with this reduction, the CAR is suitable for quantum networks.