  The strong friction regime at low temperatures is analyzed systematically
starting from the formally exact path integral expression for the reduced
dynamics. This quantum Smoluchowski regime allows for a type of semiclassical
treatment in the inverse friction strength so that higher order quantum
corrections to the original quantum Smoluchowski equation [PRL 87, 086802
(2001), PRL 101, 11903 (2008)] can be derived. Drift and diffusion coefficients
are determined by the equilibrium distribution in position and are directly
related to the corresponding action of extremal paths and fluctuations around
them. It is shown that the inclusion of higher order corrections reproduces the
quantum enhancement above crossover for the decay rate out of a metastable well
exactly.
