Phase-dependent quasiparticle tunneling in Josephson junctions: Measuring the cos-phi term with a superconducting charge qubit

TL;DR

This paper explores phase-dependent quasiparticle tunneling in a superconducting charge qubit, providing a new experimental approach to measure the cos-phi term, a long-debated feature of Josephson junctions.

Contribution

It introduces a novel experimental scheme using a superconducting charge qubit to directly measure the cos-phi term in Josephson junctions.

Findings

Demonstrated control of phase-dependent tunneling rates

Proposed a method to observe the cos-phi term independently

Provided insights into quasiparticle dynamics in superconducting circuits

Abstract

We investigate quasiparticle tunneling in a Cooper-pair box which is embedded in a superconducting ring to allow control of the total phase difference across the island. The phase affects the transition rate between different electron number parity states of the island, which can be observed in experiment by established means. The phase dependence also leads to what is known as the cos-phi term in the tunneling characteristics of classical Josephson junctions. This effect has remained controversial for decades; the proposed scheme opens an independent way to probe it.