Macroscopic quantum tunneling in a dc SQUID: Instanton splitting
Abstract
The theory of macroscopic quantum tunneling is applied to a currentbiased dc SQUID which constitutes a system of two interacting quantum degrees of freedom coupled to the environment. The decay probability is obtained in the exponential approximation for the overdamped case. Close to the critical driving force of the system, the decay of the metastable state is determined by a unique instanton solution describing the symmetric decay of the phases in each of the two Josephson juctions. Upon reducing the external driving force a new regime is reached where the instanton splits. The doubling of the decay channels reduces the decreasing of the decay rate in the quantum regime. A currenttemperature phase diagram is constructed based on the Landau theory of phase transitions. Depending on the external parameters the system develops either a first or a secondorder transition to the splitinstanton regime.
 Publication:

Physical Review B
 Pub Date:
 February 1994
 DOI:
 10.1103/PhysRevB.49.4033
 Bibcode:
 1994PhRvB..49.4033M
 Keywords:

 85.25.Dq;
 74.50.+r;
 Superconducting quantum interference devices;
 Tunneling phenomena;
 point contacts weak links Josephson effects