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The behavior of a Josephson system under pulsed operation is of utmost importance for developing reliable digital devices working at very high clock frequencies. Information about effect of thermal noise over pulsed operation is also useful to design errors free devices. Recent experiments in a system of two stacked junctions show that pulses applied to the first junction (injector) of the stack drive the Josephson biased second junction (detector) in the resistive state. The experiment was interpreted as pulsed-assisted escape toward resistive state as a consequence of an excitation of large non-linear oscillations in the detector junction that, with the contribution of thermal noise, drives out the junction from the zero voltage state. Moreover, an unstability of the resistive state toward the zero voltage state under the same pulsed operation was also noted. By means of a systematic numerical approach to the problem, we present a study of the pulsed-assisted escape using the framework of the thermal escape theory for the direct transition from zero voltage state to resistive state. We study the single junction case and a stacked configuration as examples of different systems showing pulsed-assisted escape. (C) 2002 Elsevier Science B.V. All rights reserved.

We have fabricated and characterised superconducting tunnel junctions with annular geometry for radiat ion detection. The advantage of the annular geometry is that, once the trapping has occurred the magnetic field can be switched off and there is no need to further sustain any parallel magnetic field during the detector working time. In agreement with our previous theoretical prediction we have observed the suppression of the Josephson critical current and the presence of one single resonance step in the I-V characteristic when magnetic fluxons were trapped in the: central hole of the junction. (C) 2000 Elsevier Science B.V. All rights reserved.

An experimental study of quasi-particle trapping in proximised Nb/Al layers with different Al thicknesses is presented using symmetrical 3-terminal stacked double tunnel junctions. The experimental tunnelling efficiency of such devices is measured at temperatures down to 1.2 K for different injection current rates. The role of Al layers in the intermediate electrode is discussed in terms of effective non equilibrium processes. The agreement with existing theories on nonequilibrium in such proximity structures makes these results important toward a better understanding of the underlying physics in high resolution particle spectrometers.