Efimov States of Strongly Interacting Photons

We introduce a new system to study Efimov physics based on interacting photons in cold gases of Rydberg atoms. We realize an isotropic three dimensional scattering problem by equalizing the longitudinal effective mass of the photons, arising from dispersive effects, with the transverse mass of the photons, arising from diffraction effects. We find the universal three-body parameter in this regime and characterize three-body recombination processes. We find that the Efimov bound states can be directly observed in the photonic transmission through the medium. These effects are realizable in high-density atomic ensembles and can be naturally extended to probe few-body universality beyond three bodies, as well as the role of Efimov physics in the many-body regime.