  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.
