THERMALLY ACTIVATED ESCAPE FROM THE ZERO-VOLTAGE STATE IN LONG JOSEPHSON-JUNCTIONS

We have measured the rate of thermally induced escape from the zero-vo ltage state in long Josephson junctions of both overlap and in-line ge ometry as a function of applied magnetic field. The statistical distri bution of switching currents is used to evaluate the escape rate and d erive an activation energy Delta U for the process. Because long junct ions correspond to the continuum limit of multidimensional systems, De lta U is in principle the difference in energy between stationary stat es in an infinite-dimensional potential. We obtain good agreement betw een calculated and measured activation energies for junctions with len gths a few times the Josephson penetration depth lambda(J).