Evidence for Universal Four-Body States Tied to an Efimov Trimer

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We report on the measurement of four-body recombination rate coefficients in an atomic gas.

• Our results obtained with an ultracold sample of cesium atoms at negative scattering lengths show a resonant enhancement of losses and provide strong evidence for the existence of a pair of four-body states, which is strictly connected to Efimov trimers via universal relations.
• Our findings confirm recent theoretical predictions and demonstrate the enrichment of the Efimov scenario when a fourth particle is added to the generic three-body problem.