  A Monte Carlo sampling of diagrammatic corrections to the non-crossing
approximation is shown to provide numerically exact estimates of the long-time
dynamics and steady state properties of nonequilibrium quantum impurity models.
This `bold' expansion converges uniformly in time and significantly ameliorates
the sign problem that has heretofore limited the power of real-time Monte Carlo
approaches to strongly interacting real-time quantum problems. The new approach
enables the study of previously intractable problems ranging from generic long
time nonequilibrium transport characteristics in systems with large onsite
repulsion to the direct description of spectral functions on the real frequency
axis in Dynamical Mean Field Theory.
