Photon-pair generation via bound states in the continuum in nonlinear metasurfaces

Generation of photon pairs in nonlinear materials enables the creation of non-classical entangled photon states. With ultra-thin metasurfaces, composed of optical nano-resonators, one can enable the ultimate in miniaturising nonlinear photon sources along with unprecedented configurability. We present a novel design of a nonlinear metasurface incorporating AlGaAs nanodisks with oligomer-holes, which features symmetry protected bound states in the continuum. It enables enhanced photon-pair generation at non-degenerate photon frequencies via spontaneous parametric down-conversion. This opens the potential for quantum-entanglement between photons at ultra-short time-scales across the visible and infrared regions, leading to new opportunities for quantum spectroscopy, sensing, and imaging.