  We report on the occurrence of multiple hopping and retrapping of a Brownian
particle in a tilted washboard potential. The escape dynamic has been studied
experimentally by measuring the switching current distributions as a function
of temperature in a moderately damped NbN/MgO/NbN Josephson junction. At low
temperatures the second moment of the distribution increases in agreement with
calculations based on Kramers thermal activation regime. After a turn-over
temperature T*, the shape of the distributions starts changing and width
decreases with temperature. We analyze the data through fit of the switching
probability and Monte Carlo simulations and we find a good agreement with a
model based on a multiple retrapping process.
