Saturation of the subgap quasiparticle current in Nb/AlOx/Nb high quality Josephson junctions at very low temperatures

The subgab quasiparticle current Iqp in Josephson junctions may be affected by thermal and quantum fluctuations of the electromagnetic environment. To mimic a realistic setup, the environment is assumed not to be in thermal equilibrium with the junction. At very low temperatures of the junction Iqp is finite instead of being exponentially suppressed, as predicted by the BCS theory. It depends on the impedance of the circuit. We use our simple model to interpret the observed flattening of Iqp in Nb/AlOx/Nb high quality junctions. (author)