Parametric down-conversion photon pair source on a nanophotonic chip
  Quantum photonic chips, which integrate quantum light sources alongside active and passive optical elements, as well as single photon detectors, show great potential for photonic quantum information processing and quantum technology. Mature semiconductor nanofabrication processes allow for scaling such photonic integrated circuits to on-chip networks of increasing complexity. Second order nonlinear materials are the method of choice for generating photonic quantum states in the overwhelming part of linear optic experiments using bulk components but integration with waveguide circuitry on a nanophotonic chip proved to be challenging. Here we demonstrate such an on-chip parametric down-conversion source of photon pairs based on second order nonlinearity in an Aluminum nitride microring resonator. We show the potential of our source for quantum information processing by measuring high-visibility antibunching of heralded single photons with nearly ideal state purity. Our down conversion source operates with high brightness and low noise, yielding pairs of correlated photons at MHz-rates with high coincidence-to-accidental ratio. The generated photon pairs are spectrally far separated from the pump field, providing good potential for realizing sufficient on-chip filtering and monolithic integration of quantum light sources, waveguide circuits and single photon detectors. 
Xiang Guo, Chang-ling Zou, Carsten Schuck, Hojoong Jung, Risheng   Cheng, Hong X. Tang
quant-ph physics.optics