Recombination of Three Atoms in the Ultracold Limit

Abstract

We identify two qualitatively different mechanisms that control three-body recombination in a spin-polarized gas near zero temperature. A universal curve describes the recombination rate versus the two-body scattering length $a$. It grows as ${a}^{4}$ for large $|a|,$ with different mechanisms for $a<0$ and $a>0$. Our calculations document a previously established mechanism that causes ${K}_{3}$ to grow rapidly as the two-body scattering length $a$ increases toward $+\ensuremath{\infty}$, and a new tunneling mechanism that produces an even stronger enhancement of ${K}_{3}$ as $a\ensuremath{\rightarrow}\ensuremath{-}\ensuremath{\infty}$. The expectations based on these two mechanisms can be modified by quantum mechanical interference or resonance effects.