Observation of the Borromean Three-Body Forster Resonances for Three Interacting Rb Rydberg Atoms

Three-body Forster resonances at long-range interactions of Rydberg atoms were first predicted and observed in Cs Rydberg atoms by Faoro et al. [Nat. Commun. 6, 8173 (2015)]. In these resonances, one of the atoms carries away an energy excess preventing the two-body resonance, leading thus to a Borromean type of Forster energy transfer. But they were in fact observed as the average signal for the large number of atoms N >> 1. In this Letter, we report on the first experimental observation of the three-body Forster resonances 3 x nP(3/2)(|M|) -> nS(1/2) + (n + 1)S-1/2 + nP(3/2)(|M*|) in a few Rb Rydberg atoms with n = 36, 37. We have found here clear evidence that there is no signature of the three-body Forster resonance for exactly two interacting Rydberg atoms, while it is present for N = 3-5 atoms. This demonstrates the assumption that three-body resonances can generalize to any Rydberg atom. As such resonance represents an effective three-body operator, it can be used to directly control the three-body interactions in quantum simulations and quantum information processing with Rydberg atoms.