Observation of macroscopic quantum tunnelling in a rf superconducting quantum interference device system

We present the experimental observation of the effects of macroscopic quantum tunnelling 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 a if SQUID are reported, both in the classical and quantum regimes. The low dissipation level and the good insulation of the probe from external noise are encouraging in view of building a macroscopic quantum coherent system.