The Universality of the Efimov Three-body Parameter

In this paper we discuss the recent discovery of the universality of the three-body parameter (3BP) from Efimov physics. This new result was identified by recent experimental observations in ultracold quantum gases where the value of the s-wave scattering length, a = a _?, at which the first Efimov resonance is created was found to be nearly the same for a range of atomic species — if scaled as a _?/r _vdW, where r _vdW is the van der Waals length. Here, we discuss some of the physical principles related to these observations that emerge from solving the three-body problem with van der Waals interactions in the hyperspherical formalism. We also demonstrate the strong three-body multichannel nature of the problem and the importance of properly accounting for nonadiabatic effects.