Fig. 6: Integrated LN photonic circuits for entanglement-based dual comb source generation.

Two classical comb sources with slightly different comb line spacings are generated by pumping a CW laser into coupled microresonators at normal group velocity dispersion regimes. The comb on the bottom side is split into two beam paths: one beam serves as the local comb oscillator while the other beam is sent to a PPLN waveguide for second harmonic generation, after which the SHG beam is used to generate entangled sidebands around each local comb line using a second dispersion engineered PPLN waveguide. The entangled sideband beam is then combined with the classical signal comb, together serving as the quantum signal comb output. The darker green pulse corresponds to the frequency comb at the fundamental frequency while the red pulse corresponds to the frequency comb as second harmonic frequency and the lighter green pulse illustrates the sideband engineered state at the fundamental frequency. SHG, second harmonic generation; PPLN WG, periodically poled lithium niobate waveguide; CW continuous wave.