Abstract
The quantum confinement of Rydberg excitons is an important step towards exploiting their large nonlinearities for quantum applications. We observe Rydberg excitons in natural nanoparticles of Cu₂O. We resolve up to the principal quantum number n=12 in a bulk Cu₂O crystal and up to n=6 in nanoparticles extracted from the same crystal. The exciton transitions in nanoparticles are broadened and their oscillator strengths decrease as ∝ n⁻⁴ compared to those in the bulk (decreasing as ∝ n⁻³). We explain our results by including the effect of quantum confinement of exciton states in the nanoparticles. Our results provide an understanding of the physics of Cu₂O Rydberg excitons in confined dimensions.