Towards an experiment of MQC: determination of the decoherence time from energy level quantization in rf SQUIDs

In view of realizing an experiment of Macroscopic Quantum Coherence with SQUIDs we have measured the effective resistance of a SQUID cooled at a temperature of 35mK. From a fit of the data with a simplified solution of the master equation describing the system dynamics we found an effective resistance R approximate to 4 Mn. This value, in the same system cooled at 4 mK, should lead to a decoherence time of approximately 1.4 mu s allowing to perform MQC measurements with a tunneling frequency of the order of few MHz.