Time Dependence of Few-Body Förster Interactions among Ultracold Rydberg Atoms.

Rubidium Rydberg atoms in either |m_{j}| sublevel of the 36p_{3/2} state can exchange energy via Stark-tuned Förster resonances, including two-, three-, and four-body dipole-dipole interactions. Three-body interactions of this type were first reported and categorized by Faoro et al. [Nat. Commun. 6, 8173 (2015)NCAOBW2041-172310.1038/ncomms9173] and their Borromean nature was confirmed by Tretyakov et al. [Phys. Rev. Lett. 119, 173402 (2017)PRLTAO0031-900710.1103/PhysRevLett.119.173402]. We report the time dependence of the N-body Förster resonance N×36p_{3/2,|m_{j}|=1/2}→36s_{1/2}+37s_{1/2}+(N-2)×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.