Spontaneous Parametric Down-Conversion in Nonlinear Metasurfaces

Resonant nonlinear metasurfaces gained a lot of interest in the past decade because of their unique features such as subwavelength thickness and ability to control spatial and temporal properties of light. They have proved to be efficient for classical processes such as second-harmonic generation (SHG), but their potential in quantum nanophotonics - for example for biphoton generation via spontaneous parametric down-conversion (SPDC) - remained mostly unexplored. Recently, SPDC at the nanoscale was established in nonlinear thin films [1] and implied in single nanoresonators [2], albeit with very low efficiency.