Quantum instability in a dc SQUID with strongly asymmetric dynamical parameters

A classical system cannot escape out of a metastable state at zero temperature. However, a composite system made from both classical and quantum degrees of freedom may drag itself out of the metastable state by a sequential process. The sequence starts with the tunneling of the quantum component which then triggers a distortion of the trapping potential holding the classical part. Provided this distortion is large enough to turn the metastable state into an unstable one, the classical component can escape. We show that such a composite system can be conveniently studied and implemented in a dc superconducting quantum interference device (SQUID) featuring asymmetric dynamical parameters. We determine the dynamical phase diagram of this system for various choices of junction parameters and system preparations.