Development and test of Josephson devices for an experiment of macroscopic quantum coherence

We report on the development and test of Josephson devices, namely tunnel junctions and r.f.-SQUIDs (Superconducting QUantum Interference Devices), in the framework of an experiment to detect macroscopic quantum coherence (MQC, started in 1994). To meet the stringent requirements imposed by the experiment, one needs high-quality, hysteretic Josephson junctions, with an almost ideal behavior for what concerns dissipation, even at very low temperature (down to the mK range). Such junctions must then be used inside a superconducting loop, to realize the r.f.-SQUID which is the source of the macroscopic state to be tested. We fabricated both types of devices and tested their characteristics, included the response to thermal activation, at 4.2 K and, for the junctions, down to 300 mK