Traversal time in Josephson junctions

Direct measurements of the lifetime of the zero-voltage state in a Josephson junction, operating at a temperature where the quantum contribution is comparable with the thermal escape, have been performed as a function of the bias current [1]. From these measurements the traversal time of the barrier can be deduced according to a semiclassical analysis, analogously to what was previously done by measuring the dependence of the lifetime on the load of the junction [2]. The semiclassical traversal time, which turns out to be on the order of 100 ps, is presumably only the imaginary part of a complex quantity whose real part remains unknown (and is also not accessible to direct measurement). An estimate of this quantity can be done along the lines of a theoretical model which considers tunneling to be a stochastic process, anti the real part of the traversal time turns out to be on the order of a few picoseconds. The connection with the Zeno time is also considered.