Quantum modeling of a current-driven Josephson oscillator

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Abstract
Using field-theoretic techniques we develop a quantum model of a current-biased Josephson junction that explicitly takes into account the external drive wires. In addition to generating the current, we find that the external wires also affect the degree of phase order across the junction oxide. As a specific application of our approach, we examine the steady-state dynamics of a Josephson oscillator that is current biased on a Shapiro step and exposed to a random-noise current which flows in a direction normal to the tunneling current. For certain values of the system parameters, we find that the dc pair current exhibits a markedly different dependence on the rf power than occurs in the usual Shapiro current. It is also shown that the nature of the phase coherence for this situation is considerably different from the usual Josephson state.