Energy levels quantization in underdamped Josephson junctions

we have measured the switching current distributions out of the zero-voltage state of Josephson junctions in nonstationary conditions, obtained by means of fast sweeping of the current bias resulting in a dI/dt up to 25 A/sec. In this way we have analysed the effects of the levels quantization on the escape rate out of the zero voltage state in conditions where the occupancy probability of the energy levels is far from being in equilibrium.