Crystalline superconductor-semiconductor Josephson junctions for compact superconducting qubits

TL;DR

This paper demonstrates the use of crystalline superconductor-semiconductor Josephson junctions, specifically WSe2, to create compact, stable superconducting qubits with tunable properties and strong coupling to microwave resonators.

Contribution

It introduces a new platform using van der Waals heterostructures for superconducting qubits, showing robust Josephson coupling and successful fabrication of a prototype transmon qubit.

Findings

Robust Josephson coupling observed across 2-12 nm of WSe2

Crossover from proximity- to tunneling-type behavior with increasing thickness

Prototype transmon qubit with matching design parameters and microwave coupling

Abstract

The narrow bandgap of semiconductors allows for thick, uniform Josephson junction barriers, potentially enabling reproducible, stable, and compact superconducting qubits. We study vertically stacked van der Waals Josephson junctions with semiconducting weak links, whose crystalline structures and clean interfaces offer a promising platform for quantum devices. We observe robust Josephson coupling across 2--12 nm (3--18 atomic layers) of semiconducting WSe$_2$ and, notably, a crossover from proximity- to tunneling-type behavior with increasing weak link thickness. Building on these results, we fabricate a prototype all-crystalline merged-element transmon qubit with transmon frequency and anharmonicity closely matching design parameters. We demonstrate dispersive coupling between this transmon and a microwave resonator, highlighting the potential of crystalline superconductor-semiconductor structures for compact, tailored superconducting quantum devices.