Nonlinearity symmetry breaking for generating tunable quantum entanglement in semiconductor metasurfaces

Abstract

Tunable biphoton quantum entanglement generated from nonlinear flat optics is highly desirable for cutting-edge quantum technologies, yet its tunability is substantially constrained by the symmetry of material nonlinear tensors. Here, we overcome this constraint by introducing symmetry breaking in nonlinear polarization via resonant metasurfaces. While asymmetric optical responses have enabled breakthroughs in classical applications like nonreciprocal light transmission, we report the experimental demonstration of asymmetric nonlinear responses for biphoton entanglement. Using a structural-asymmetric semiconductor metasurface incorporating [110] InGaP nanoresonators, we realize continuous tu..