Yanqing Lu

Quantum network facilitates the secure transmission of information between different users. Establishing communication links among multiple users in a scalable and efficient way is important for realizing large-scale quantum network. Here we develop a time-energy entanglement-based dense wavelength division multiplexed network based on an integrated silicon nitride micro-ring resonator, which offers a wide frequency span (>100 nm) and narrow bandwidth modes (~ 5 pm). Six pairs of photons are selected to form a fully and simultaneously connected four-user quantum network. The observed quantum interference visibilities are well above the classical limits among all users. Our result paves the way for realizing large-scale quantum networks with integrated photonic architecture.

Integrated photonics provides a route both to miniaturize quantum key distribution (QKD) devices and to enhance their performance. A key element for discrete-variable QKD is single-photon detector. It is necessary to integrate such device onto a photonic chip to enable the realization of practical and scalable quantum networks. Here, we report a successful interfacing of Complementary Metal-Oxide-Semiconductor (CMOS)-compatible silicon nanophotonics with optical waveguide-integrated superconducting nanowire single-photon detector (SNSPD). We perform the first optimal Bell-state measurement (BSM) of time-bin encoded qubits generated from two independent lasers benefited from the reduced dead time of SNSPD ∼3.4 ns. The optimal BSM enables an increased key rate of measurement-device-independent QKD, which is immune to all attacks against the detection system and hence provides the basis for a QKD network with untrusted relays. Together with the time-multiplexed technique, we have enhanced the sifted key rate by almost one order of magnitude. Combined with integrated QKD transmitters, a scalable, chip-based and cost-effective QKD network should become realizable in the near future.