Rydberg excitons in Cu ₂ O: exaggerated quantum optical properties and emerging quantum phenomena [Invited]

Over the past decade, Rydberg excitons in bulk Cu 2 O have emerged as a solid-state analog to atomic Rydberg systems, exhibiting exaggerated quantum optical properties including large dipole moments, strong dipole–dipole interactions, and enhanced nonlinear susceptibilities. High-resolution absorption spectroscopy has revealed elegant scaling laws with principal quantum number across temperatures from tens of mK to above 100 K. While many features follow a hydrogen-like model, non-hydrogenic effects arise from complex bandstructures and many-body interactions. This review summarizes experimental advances in accessing high- n Rydberg states and quantum phenomena arising from diverse exciton interaction mechanisms. It also discusses prospective quantum and nonlinear optical applications.