Foundry-fabricated sources of broadband entanglement

A photonic integrated circuit (PIC) comprising:

• a microring resonator (MRR) configured to:
• receive first pump having a first polarization mode, the first pump having a pump frequency fP that matches a resonant frequency of the MRR, the MRR configured to guide the first pump in a first direction through the MRR;
• produce, from the first pump, respective first frequency-correlated photon pairs via a nonlinear optical interaction supported by the MRR, subject to energy conservation, each respective first frequency-correlated photon pair having signal mode with a signal frequency fS and idler mode having an idler frequency fI, and guide them in the first direction through the MRR,
• receive second pump having the first polarization, the second pump having the pump frequency fP, the MRR configured to guide the second pump in a second direction through the MRR, the second direction being opposite to the first direction;
• and
• produce, from the second pump, respective second frequency-correlated photon pairs via the nonlinear optical interaction supported by the MRR, subject to energy conservation, each respective second frequency-correlated photon pair having a signal mode with the signal mode frequency fS and idler mode having the idler mode frequency fI, and guide them in the second direction through the MRR;
• a first waveguide disposed upstream from the MRR, the first waveguide being evanescently coupled to the MRR, the first waveguide is configured to transfer the first pump and the second pump to the MRR, wherein the first pump propagates in the second direction within the first waveguide and the second pump propagates in the first direction within the first waveguide;
• a second waveguide disposed downstream from the MRR, the second waveguide being evanescently coupled to the MRR, the second waveguide configured to:
• receive the respective first frequency-correlated photon pairs from the MRR and guide them in the second direction through the second waveguide;
• and
• receive the respective second frequency-correlated photon pairs from the MRR and guide them in the first direction through the second waveguide;
• and
• a polarization splitter rotator (PSR) arranged and configured to
• receive, from the second waveguide, the respective first and second frequency-correlated photon pairs comprising respective signal and idler modes, apply a common polarization rotation to photons of either the respective first or second frequency-correlated photon pairs in a polarization basis comprising mutually orthogonal polarization modes such that the signal and idler within each pair share the same polarization and the polarization mode of the respective first frequency-correlated photon pairs is orthogonal to the respective second frequency-correlated photon pairs, and
• combine, post-rotation, all pairs to output a first polarization-entangled Bell State.