Rydberg blockade in an ultracold strontium gas revealed by two-photon excitation dynamics

Abstract

We demonstrate the interaction-induced blockade effect in an ultracold $^{88}\mathrm{Sr}$ gas via studying the time dynamics of a two-photon excitation to the triplet Rydberg series $5sns{\phantom{\rule{0.16em}{0ex}}}^{3}{S}_{1}$ for five different principal quantum numbers $n$ ranging from 19 to 37. By using a multipulse excitation sequence to increase the detection sensitivity, we could identify Rydberg-excitation-induced atom losses as low as $<1%$. Based on an optical Bloch equation formalism, treating the Rydberg-Rydberg interaction on a mean-field level, the van der Waals coefficients are extracted from the observed dynamics, which agree fairly well with ab initio calculations.