Microwave spectroscopy of Andreev states in InAs nanowire-based hybrid junctions using a flip-chip layout

TL;DR

This paper reports on the fabrication and microwave spectroscopy of InAs nanowire-based Josephson junctions, revealing detailed Andreev state transitions crucial for quantum computing applications.

Contribution

It introduces a flip-chip fabrication method for high-quality superconducting circuits and provides spectroscopic insights into Andreev states in nanowire junctions.

Findings

Observation of single quasiparticle transitions

Detection of quasiparticle pair transitions

Junction operates in the intermediate channel length regime

Abstract

Josephson junctions based on semiconductor nanowires are potential building blocks for electrically tunable qubit structures, e.g. the gatemon or the Andreev qubit. However, an actual realization requires the thorough investigation of the intrinsic excitation spectrum. Here, we demonstrate the fabrication of low-loss superconducting microwave circuits that combine high quality factors with a well-controlled gate architecture by utilizing a flip-chip approach. This platform is then used to perform single-tone and two-tone experiments on Andreev states in in-situ grown InAs/Al core/half-shell nanowires with shadow mask defined Josephson junctions. In gate-controlled and flux-biased spectroscopic measurements we find clear signatures of single quasiparticle as well as quasiparticle pair transitions between discrete Andreev bound states mediated by photon-absorption. Our experimental findings are supported by simulations that show that the junction resides in the intermediate channel length regime.