Andreev Spectroscopy for Superconductive Phase Qubit

Abstract

New method to probe quantum dynamics of the order parameter phase of a small superconductive island is proposed. The idea is to measure Andreev subgap conductance between the island and a dirty normal-metal wire connected with the island by very high-resistance tunnel barrier. The phase on the island is supposed to stay primarly in one of the two nearly degenerate classical minima i.e. the island is an active element of the Superconductive Phase Qubit. Voltage-dependence of the differential subgap conductance measured at low temperatures are predicted to demonstrate crucially different behavior depending on the type of the internal dynamics of phase (coherent tunnelling of phase, non-coherent tunnelling, or no tunneling). Thus the measurements of nonliner Andreev conductance is a tool to probe the type of quantum behavior of the artificial two-level system.