Universal van der Waals Physics for Three Ultracold Atoms

Experimental studies with ultracold atoms have enabled major breakthroughs in understanding three-body physics, historically a fundamental yet challenging problem. This is because the interactions among ultracold atoms can be precisely varied using magnetically tunable scattering resonances known as Feshbach resonances. The collisions of ultracold atoms have been discovered to have many universal aspects near the unitarity limit. Away from this limit, many quantum states are expected to be active during a three-body collision, making the collisional observables practically unpredictable. Here we report a major development in predicting three-body ultracold scattering rates by properly building in the pairwise van der Waals interactions plus the multi-spin properties of a tunable Feshbach resonance state characterized by two known dimensionless two-body parameters. Numerical solution of the Schr{\"o}dinger equation then predicts the three-atom collisional rates without adjustable fitting parameters needed to fit data. Our calculations show quantitative agreement in magnitude and feature position and shape across the full range of tuning of measured rate coefficients for three-body recombination and atom-dimer collisions involving ultracold Cs atoms.