Measurement of the effect of moderate dissipation on macroscopic quantum tunneling

Abstract
The escape rate Γ(T) from the zero voltage state has been measured for a current-biased Josephson tunnel junction shunted with a normal metal resistor. Values of Γ(T) measured at the lowest temperature of the experiment, 18 mK, and extrapolated to T=0 are in excellent agreement with the predictions for macroscopic quantum tunneling that include a reduction by a factor of about 300 for the effect of dissipation. Above the crossover temperature, the enhancement of Γ(T) over the rate for thermal activation is in good agreement with predicted quantum corrections.