  Lifetimes of complexes formed during ultracold collisions are of current
experimental interest as a possible cause of trap loss in ultracold gases of
alkali-dimers. Microsecond lifetimes for complexes formed during ultracold
elastic collisions of K2 with Rb are reported, from numerically-exact
quantum-scattering calculations. The reported lifetimes are compared with those
calculated using a simple density-of-states approach, which are shown to be
reasonable. Long-lived complexes correspond to narrow scattering resonances
which we examine for the statistical signatures of quantum chaos, finding that
the positions and widths of the resonances follow the Wigner-Dyson and
Porter-Thomas distributions respectively.
