  Dissipation encodes interaction of a quantum system with the environment and
regulates the activation regimes of a Brownian particle. We have engineered
grain boundary biepitaxial YBaCuO junctions to drive a direct transition from
quantum activated running state to phase diffusion regime. The cross-over to
the quantum regime is tuned by the magnetic field and dissipation is encoded in
a fully consistent set of junction parameters. To unravel phase dynamics in
moderately damped systems is of general interest for advances in the
comprehension of retrapping phenomena and in view of quantum hybrid technology.
