# Large spatial extension of the zero-energy Yu-Shiba-Rusinov state in magnetic field

## TL;DR

This study reveals that the zero-energy Yu-Shiba-Rusinov state in a semiconductor quantum dot coupled to a superconductor extends over more than 50 nm, with its size significantly increasing under magnetic field, advancing understanding for quantum technology applications.

## Contribution

First experimental and theoretical investigation of the spatial extension of a Shiba state in a semiconductor quantum dot coupled to a superconductor.

## Key findings

- Shiba state extends over more than 50 nm.
- Spatial extension increases substantially with magnetic field.
- Extension is larger than previously observed in STM measurements.

## Abstract

Various promising qubit concepts have been put forward recently based on engineered superconductor (SC) subgap states like Andreev bound states, Majorana zero modes or the Yu-Shiba-Rusinov (Shiba) states. The coupling of these subgap states via a SC strongly depends on their spatial extension and is an essential next step for future quantum technologies. Here we investigate the spatial extension of a Shiba state in a semiconductor quantum dot coupled to a SC for the first time. With detailed transport measurements and numerical renormalization group calculations we find a remarkable more than 50 nm extension of the zero energy Shiba state, much larger than the one observed in very recent scanning tunneling microscopy (STM) measurements. Moreover, we demonstrate that its spatial extension increases substantially in magnetic field.