  The operation of long-distance quantum networks requires photons to be
synchronized and must account for length variations of quantum channels. We
demonstrate a 200 MHz clock-rate fiber optic-based quantum network using
off-the-shelf components combined with custom-made electronics and
telecommunication C-band photons. The network is backed by a scalable and fully
automated synchronization system with ps-scale timing resolution.
Synchronization of the photons is achieved by distributing O-band-wavelength
laser pulses between network nodes. Specifically, we distribute photon pairs
between three nodes, and measure a reduction of coincidence-to-accidental ratio
from 77 to only 42 when the synchronization system is enabled, which permits
high-fidelity qubit transmission. Our demonstration sheds light on the role of
noise in quantum communication and represents a key step in realizing deployed
co-existing classical-quantum networks.
