# Spectroscopy of the superconducting proximity effect in nanowires using integrated quantum dots

## TL;DR

This study uses integrated quantum dots in InAs nanowires to perform detailed spectroscopy of the superconducting proximity effect, revealing how the proximity gap varies with electron density and enabling future exploration of Majorana states.

## Contribution

It introduces a novel device architecture with spatially separated quantum dots for precise spectroscopy of proximity-induced states in nanowires, advancing the study of topological quantum phenomena.

## Key findings

- Proximity gap is suppressed at low electron densities and fully developed at higher densities.
- The transition from long to short junction regimes is gate-tunable.
- The architecture enables systematic studies of subgap bound states.

## Abstract

The superconducting proximity effect has been the focus of significant research efforts over many years and has recently attracted renewed interest as the basis of topologically non-trivial states in materials with a large spin orbit interaction, with protected boundary states useful for quantum information technologies. However, spectroscopy of these states is challenging because of the limited spatial and energetic control of conventional tunnel barriers. Here, we report electronic spectroscopy measurements of the proximity gap in a semiconducting indium arsenide (InAs) nanowire (NW) segment coupled to a superconductor (SC), using a spatially separated quantum dot (QD) formed deterministically during the crystal growth. We extract the characteristic parameters describing the proximity gap which is suppressed for lower electron densities and fully developed for larger ones. This gate-tunable transition of the proximity effect can be understood as a transition from the long to the short junction regime of subgap bound states in the NW segment. Our device architecture opens up the way to systematic, unambiguous spectroscopy studies of subgap bound states, such as Majorana bound states.