This paper proposes and experimentally demonstrates a weakly-interacting many-body system of Rydberg polaritons using an electromagnetically induced transparency (EIT) medium with high optical depth (OD) and Rydberg atoms with a low principal quantum number. Significant phase shift and attenuation, attributed to dipole-dipole interactions (DDI), were observed, representing elastic and inelastic collisions. A cooling effect was also demonstrated through a reduction in the width of the transverse momentum distribution. The long interaction time and large collision cross-section suggest the feasibility of polariton Bose-Einstein condensation.

Bongjune Kim, Ko-Tang Chen, Shih-Si Hsiao, Sheng-Yang Wang, Kai-Bo Li, Julius Ruseckas, Gediminas Juzeliūnas, Teodora Kirova, Marcis Auzinsh, Ying-Cheng Chen, Yong-Fan Chen, Ite A. Yu