Full Shapiro spectroscopy of current-phase relationships

TL;DR

This paper introduces a novel, non-invasive method to fully characterize the current-phase relationship of a superconducting junction by analyzing its response to ac driving, validated through simulations and experiments.

Contribution

The paper presents a new driving-based technique to extract the complete harmonic content of the CPR, improving upon traditional methods that are more invasive.

Findings

Method accurately retrieves full CPR harmonic content

Works effectively even with noisy data

Validated through simulations and experimental data

Abstract

Extracting the current-phase relationship (CPR) of a single superconducting junction is challenging in practice and traditionally involves embedding the junction in a larger superconducting circuit containing SQUIDs and/or resonators. Applying ac driving to the junction has proven to be a viable and less invasive way to extract information about the few lowest harmonics of the CPR, by locating the integer and fractional Shapiro steps in the IV-curve of the driven junction. Here, we present an alternative driving-based method that allows to extract the full harmonic content of a CPR in a non-invasive way, by fitting the measured critical currents of the driven junction as a function of driving power. We test our method, both using numerical simulations and in experiments, and we show that it works very accurately, also in the presence of noise.