Observation of Macroscopic Quantum Tunnelling in a rf SQUID system

We present the experimental observation of the effects of Macroscopic Quantum Tunneling in a SQUID device, consisting of a rf SQUID coupled to a readout system based on a dc SQUID sensor. Data on the decay rate from the metastable flux states of rf SQUID are reported, both in the classical and quantum regimes. The low dissipation level and the good insulation of the probe from the external noise are encouraging in view of building a macroscopic quantum coherent system.