  We investigate, by experiments and numerical simulations, thermal activation
processes of Josephson tunnel junctions in the presence of microwave radiation.
When the applied signal resonates with the Josephson plasma frequency
oscillations, the switching current may become multi-valued temperature ranges
both below and above the the classical to quantum crossover temperature.
Switching current distributions are obtained both experimentally and
numerically at temperatures both near and far above the quantum crossover
temperature. Plots of the switching currents traced as a function of the
applied signal frequency show very good agreement with a simple anharmonic
theory for Josephson resonance frequency as a function of bias current.
Throughout, experimental results and direct numerical simulations of the
corresponding thermally driven classical Josephson junction model show very
good agreement.
