Picosecond clock synchronization across a 7-node metropolitan scale quantum network

Quantum networking protocols relying on interference and precise time-of-flight measurements require highprecision clock synchronization. This study describes the design, implementation, and characterization of two optical time transfer methods in a metropolitan-scale quantum networking research testbed. The first technique called active electronic stabilization (ELSTAB), was able to achieve sub-picosecond time deviation (TDEV) at integration times between 1 s and 105 s over multiple different fiber lengths of both underground and aerial deployed fiber. The second technique, White Rabbit-Precision Time Protocol (WR-PTP), was able to achieve 10-picosecond TDEV’s over similar fiber lengths at comparable integration times. Environmental fluctuations affected the stability of clock synchronization over deployed fiber. These fluctuations resulted in path delay gradients, chromatic dispersion, polarization drift, and optical power variations. The results from this study will inform future work in the development of compensation methods essential for enabling experimental research in developing practical quantum networking protocols.