Rydberg excitons have only recently been discovered. They are highly-excited, bound electron-hole pairs that represent giant atom-like quasiparticles in a semiconductor environment. These new particles defy conventional theories of exciton physics and open fundamentally new regimes for quantum optics with excitons.
Here, I will show how their remarkable properties originate from strong, long-range polarization forces acting between pairs of such states over thousands of crystal cells, suggesting great potential for optical applications. We develop a semi-analytical cluster-expansion theory to describe the enormous optical nonlinearity of the Rydberg interactive many-body system, revealing the effect of a residual thin electron-hole plasma and bringing our theory into quantitative agreement with corresponding experiments.
However, strong phonon coupling and inter-band dynamics can complicate this simple atom-like picture and limit the usability of Rydberg-Rydberg interactions for optical applications. Using experiments with cuprous oxide as an example, I will discuss the origins of phonon coupling and how the formation of an optical dark state can be used to mitigate its undesired effects. Finally, I will describe ongoing efforts to exploit strong Rydberg interactions of excitons in monolayered semiconductors for the creation of nonclassical light. Our results open the stage for physics with strongly interacting polaritons in the solid state, making it possible to induce nonlinear processes at the level of individual photons.
