A weakly-interacting many-body system of Rydberg polaritons based on electromagnetically induced transparency

The combination of Rydberg atoms and electromagnetically induced transparency (EIT) has been extensively studied in the strong-interaction regime. Here we proposed utilizing an EIT medium with a high optical depth (OD) and a Rydberg state of low principal quantum number to create a many-body system of Rydberg polaritons in the weak-interaction regime. The phase shift and attenuation induced by the dipole–dipole interaction (DDI) were still significant, and can be viewed as the consequences of elastic and inelastic collisions among Rydberg polaritons. We further observed that the width of the transverse momentum distribution of Rydberg polaritons at the exit of the system became notably smaller as compared with that at the entrance. The observation demonstrates the cooling effect in this system. The μs-long interaction time due to the high-OD EIT medium plus the μm 2 -size collision cross section due to the DDI suggests a feasible platform of polariton Bose–Einstein condensation. Rydberg-state atoms are characterized by significant dipole–dipole interaction making them useful for quantum information applications. The authors present experimental results on a high-optical-depth electromagnetically-induced-transparency medium of weakly interacting Rydberg atoms as a way of realizing Bose–Einstein condensates of polaritons.