Andreev Modes from Phase Winding in a Full-shell Nanowire-based Transmon

TL;DR

This paper explores how phase winding in fully-shell nanowire transmons influences Andreev states and qubit coherence, revealing the impact of magnetic flux and shell properties on quantum behavior.

Contribution

It demonstrates the role of phase winding and Andreev states in transmon qubits made from nanowires with a superconducting shell, supported by experimental and numerical analysis.

Findings

Coherent transitions occur in the first reentrant lobe with phase winding.

Qubit coherence diminishes as junction density increases.

Numerical simulations support the role of winding-induced Andreev states.

Abstract

We investigate transmon qubits made from semiconductor nanowires with a fully surrounding superconducting shell. In the regime of reentrant superconductivity associated with the destructive Little-Parks effect, numerous coherent transitions are observed in the first reentrant lobe, where the shell carries 2{\pi} winding of superconducting phase, and are absent in the zeroth lobe. As junction density was increased by gate voltage, qubit coherence was suppressed then lost in the first lobe. These observations and numerical simulations highlight the role of winding-induced Andreev states in the junction.