Low-temperature behaviour of Josephson junctions for the MQC (Macroscopic Quantum Coherence) experiment

The behaviour of Nb/AlO/sub x//Nb Josephson junctions has been investigated, between 4.2 and 0.3 K, in view of their use in a Macroscopic Quantum Coherence (MQC) experiment. Particular emphasis has been devoted to dissipation and thermalization, since the possibility of performing a MQC experiment relies on high-quality Josephson junctions, which must be in the quantum regime at temperatures of the order of 10 mK and must have low dissipation, in order not to wash out the coherence effect to be detected.