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 WSe2 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.
@article{arxiv.2501.14969,
title = {Crystalline superconductor-semiconductor Josephson junctions for compact superconducting qubits},
author = {Jesse Balgley and Jinho Park and Xuanjing Chu and Ethan G. Arnault and Martin V. Gustafsson and Leonardo Ranzani and Madisen Holbrook and Yangchen He and Kenji Watanabe and Takashi Taniguchi and Daniel Rhodes and Vasili Perebeinos and James Hone and Kin Chung Fong},
journal= {arXiv preprint arXiv:2501.14969},
year = {2025}
}