Fig. 1. (Color online) Integrated silicon photonic QKD transmitters. (a) Polarization-encoding PM-QKD transmitter, consisting of ring modulators, VOAs, and polarization modulators^[12]. (b) Three implementations of high-speed QKD^[11]. (c) HOM interference between WCPs generated by III–V on silicon waveguide integrated lasers^[22]. (d) Polarization-encoding MDI-QKD with integrated silicon photonics^[24].

Fig. 2. (Color online) Integrated InP photonic QKD transmitters. (a) A chip-to-chip QKD system between a 2 × 6 mm² InP transmitter and a 2 × 32 mm² SiO_xN_y receiver^[16]. (b) An implementation of MDI-QKD using two 6 × 2 mm² InP transmitter chips in which two weak coherent states are on-chip generated independently^[25].

Fig. 3. (Color online) On-chip entangled photon sources. (a) Generation of entangled photons from a single quantum dot embedding in photonic nanostructures^[34]. (b) Generation of entangled photons in a thin-film waveguide using the SPDC process^[35]. (c) Generation of entangled photons in a silicon photonic microring resonator using SFWM process^[46].

Fig. 4. (Color online) Chip-based entanglement distribution and quantum teleportation. (a) Silicon photonic circuit diagram for a chip-to-chip entanglement distribution experiment^[49], and (b) for a chip-to-chip quantum teleportation experiment^[52], (c) scheme of a visible-telecom entanglement experiment in the silicon nitride system^[53].

Fig. 5. (Color online) Integrated quantum memories in the ERIC system. (a) An optical microscope image of five quantum memories in laser-written optical waveguides^[75]. (b) A scanning electron microscope image of a quantum memory integrated in a photonic crystal nanocavity^[78].