Time dependence of few-body Förster interactions among ultracold Rydberg atoms

Abstract: Rubidium Rydberg atoms in either $|m_j|$-sublevel of the $36p_{3/2}$ state can exchange energy via Stark-tuned F\"{o}rster resonances, including two-, three-, and four-body dipole-dipole interactions. Three-body interactions of this type were first reported and categorized by Faoro, \textit{et al.}~[Nat.\ Commun.\ \textbf{6}, 8173 (2015)] and their Borromean nature was confirmed by Tretyakov, \textit{et al.}~[Phys.\ Rev.\ Lett. \textbf{119}, 173402 (2017)]. We report the time dependence of the $N$-body F\"{o}rster resonance $N\times 36p_{3/2,|m_j|=1/2}\rightarrow 36s_{1/2}+37s_{1/2}+(N-2)\times 36p_{3/2,|m_j|=3/2}$, for $N=2,3$, and 4, by measuring the fraction of initially excited atoms that end up in the $37s_{1/2}$ state as a function of time. The essential features of these interactions are captured in an analytical model that includes only the many-body matrix elements and neighboring atom distribution. A more sophisticated simulation reveals the importance of beyond-nearest-neighbor interactions and of always-resonant interactions.