Long-lived complexes and chaos in ultracold molecular collisions

Estimates for the lifetime of collision complexes formed during ultracold molecular collisions based on density-of-states arguments are shown to be consistent with similar estimates based on classical trajectory calculations. In the classical version, these collisions are shown to exhibit chaos and their fractal dimension is calculated versus collision energy. From these results, a picture emerges that ultracold collisions are likely classically ergodic, justifying the density-of-states estimates for lifetimes. These results point the way toward using the techniques of classical and quantum chaos to interpret molecular collisions in the ultracold regime.