Pascal Naidon, Shimpei End?, Masahito Ueda
Several experiments  with different kinds of ultra-cold atoms have revealed that the three-body parameter that fixes the Efimov spectrum of few-atom systems near broad Feshbach resonances is universally determined by the atoms' van der Waals length. Using model potential calculations, as well as a simple ansatz wavefunction, we find that the three-body parameter originates from a deformation of the three-atom system due to universal two-body correlations at separations on the order of the van der Waals length scale . This simple physical picture is consistent with the universality of the three-body parameter observed in the experiments , as well as previous numerical calculations . It explains why the low-energy physics of three bosonic atoms near a broad resonance is solely determined by their two-body parameters.
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