Quantum theory of the dc Josephson effect: Current-biased eigenstates and excitation spectrum

Abstract

We derive the eigenstates and excitation spectrum of a Josephson junction biased on the zero-voltage, dc current step. It is found that the detailed properties of the junction wave function depend sensitively on the amount of pair current driven through the diode. In particular, near maximum current the ground state consists of only a few definite pair difference states, which differs considerably from intuitive notions based on the tight-binding approximation.