Quantum fluctuations in a microscopic model of a Josephson junction including dissipative effects, parametrized by $\eta =\frac{\hslash }{2\pi e^{2}R}$ with $R$ the resistance, are discussed. It is shown that the parameter space divides sharply into two regions: One in which scaling trajectories lead to a vanishing mean tunneling rate at $T=0\mathrm{}$ and the other in which they do not.

• Received 14 June 1982

DOI:https://doi.org/10.1103/PhysRevLett.49.681