Effect of Dissipation on Macroscopic Quantum Tunneling

We report measurements of the escape rate from the zero-voltage state of a current-biased Josephson junction shunted by a normal-metal resistor. The critical current, capacitance, and resistance of the junction were measured in the classical regime. The escape rate was measured in both the high-temperature regime, where thermal activation dominates, and in the low-temperature regime, where macro-scopic quantum tunneling dominates. The measured escape rates are in good agreement with the predicted escape rates with respect to both the effect of dissipation and the existence of quantum corrections to thermal activation.