A Weakly-Interacting Many-Body System of Rydberg Polaritons Based on Electromagnetically Induced Transparency

TL;DR

This paper demonstrates a weakly-interacting many-body system of Rydberg polaritons using high optical depth EIT, showing elastic collisions lead to thermalization and suggesting a platform for Bose-Einstein condensation.

Contribution

It experimentally verifies the mean field approach for weakly-interacting Rydberg polaritons and observes DDI-induced phase shifts and thermalization effects.

Findings

Observed phase shift and attenuation due to DDI

Noted reduction in momentum distribution width with increased DDI

Elastic collisions drive thermalization in the system

Abstract

We proposed utilizing a medium with a high optical depth (OD) and a Rydberg state of low principal quantum number, $n$, to create a weakly-interacting many-body system of Rydberg polaritons, based on the effect of electromagnetically induced transparency (EIT). We experimentally verified the mean field approach to weakly-interacting Rydberg polaritons, and observed the phase shift and attenuation induced by the dipole-dipole interaction (DDI). The DDI-induced phase shift or attenuation can be viewed as a consequence of the elastic or inelastic collisions among the Rydberg polaritons. Using a weakly-interacting system, we further observed that a larger DDI strength caused a width of the momentum distribution of Rydberg polaritons at the exit of the system to become notably smaller as compared with that at the entrance. In this study, we took $n =32$ and the atomic (or polariton) density of 5$\times10^{10}$ (or 2$\times10^{9}$) cm$^{-3}$. The observations demonstrate that the elastic collisions are sufficient to drive the thermalization process in this weakly-interacting many-body system. The combination of the $\mu$s-long interaction time due to the high-OD EIT medium and the $\mu$m$^2$-size collision cross section due to the DDI suggests a new and feasible platform for the Bose-Einstein condensation of the Rydberg polaritons.