Spin-orbit splitting of Andreev states revealed by microwave spectroscopy

TL;DR

This study uses microwave spectroscopy to reveal spin-split Andreev states in InAs-Al nanowire Josephson junctions, demonstrating the addressability of spin states for quantum control.

Contribution

It provides the first experimental observation of spin-split Andreev states in nanowire Josephson junctions and introduces a simple model including Rashba spin-orbit interaction.

Findings

Observation of four-line crossing features at phase differences 0 and π.

Identification of zero-field spin-split Andreev states.

Model explaining the evolution of spectra with magnetic field.

Abstract

We have performed microwave spectroscopy of Andreev states in superconducting weak links tailored in an InAs-Al (core-full shell) epitaxially-grown nanowire. The spectra present distinctive features, with bundles of four lines crossing when the superconducting phase difference across the weak link is 0 or $\pi.$ We interpret these as arising from zero-field spin-split Andreev states. A simple analytical model, which takes into account the Rashba spin-orbit interaction in a nanowire containing several transverse subbands, explains these features and their evolution with magnetic field. Our results show that the spin degree of freedom is addressable in Josephson junctions, and constitute a first step towards its manipulation.