Macroscopic Quantum Tunneling and Thermal Activation from Metastable States in a dc SQUID

Abstract

We have studied the transition rate from metastable wells in the two-dimensional potential of a dc SQUID as a function of applied flux and temperature. We observe a crossover from thermally activated escape to macroscopic quantum tunneling at a flux-dependent temperature. The thermal rates are significantly suppressed, suggesting that the potential barrier for activation is effectively enhanced by the interaction of the macroscopic degrees of freedom in the device.