We present a real field quantum key distribution link based on energy-time entanglement. Three nodes are connected over the city of Nice by means of optical fibers with a total distance of 50 km. We have implemented a high-quality source of energy-time entangled photon pairs and actively stabilized analysers to project the quantum states, associated with an innovative remote synchronization method of the end stations' clocks which does not require any dedicated channel. The system is compatible with the ITU 100 GHz standard telecomgrid, through which a raw key rate of 40 kbps per pair of channels is obtained. A post-treatment software performs all the necessary post-processing procedures enabling to establish secret keys in real time. All of those embedded systems and achieved performance make this network the first fully operational entanglement based metropolitan quantum network to be implemented in real field.

We report a raw quantum interference visibility of 90 ± 1% between telecom photons emitted by a weak coherent state source (WCSS) and an entangled photon pair source (EPPS).

We achieve a frequency conversion interface to coherently transmit light from a weak coherent source at 925 nm toward telecommunication C-band. We demonstrate coherence preservation and an internal conversion of 62 % efficiency.