Macroscopic resonant tunneling of magnetic flux

We have developed a quantitative theory of resonant tunneling of magnetic f lux between discrete macroscopically distinct quantum states in superconduc ting quantum interference device systems. The theory is based on the standa rd density-matrix approach. Its elements include the discussion of the two different relaxation mechanisms that exist for the double-well potential, a nd description of the "photon-assisted" tunneling driven by external rf rad iation. It is shown that in the case of coherent flux dynamics, rf radiatio n should lead to splitting of the peaks of resonant flux tunneling, indicat ing that the resonant tunneling is a convenient tool for studying macroscop ic quantum coherence of flux.