Quantum coherence in a mesoscopic Josephson junction with dissipation

A mesoscopic Josephson junction in a superconducting ring enclosing a magnetostatic flux with dissipation is considered. The dissipation in this system is described as a consequence of its coupling to a reservoir. By solving the master equation it is shown that the state of the junction can evolve into a quantum superposition of two coherent states even when the dissipation is present. It is also shown that squeezing effects can exist in such a system, and the dynamic behavior of the supercurrent shows collapse and revival phenomena. The quantum decoherence is also discussed.