  We use numerically exact quantum Monte Carlo (QMC) to compute the properties
of three-dimensional bipolarons for interaction strengths where perturbation
theory fails. For intermediate electron-phonon coupling and Hubbard U, we find
that bipolarons can be both small and light, a prerequisite for bipolaron
superconductivity. We use the QMC results to make estimates of transition
temperatures, which peak at between 90-120 K and are demonstrated to be
insensitive to Coulomb repulsion and impurities.
