Crystalline superconductor-semiconductor Josephson junctions for compact superconducting qubits

Jesse Balgley; Jinho Park; Xuanjing Chu; Ethan G. Arnault; Martin V. Gustafsson; Leonardo Ranzani; Madisen Holbrook; Yangchen He; Kenji Watanabe; Takashi Taniguchi; Daniel Rhodes; Vasili Perebeinos; James Hone; Kin Chung Fong

doi:10.1103/3ssz-jjt6

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Crystalline superconductor-semiconductor Josephson junctions for compact superconducting qubits

Jesse Balgley ^1,*, Jinho Park ^1,*, Xuanjing Chu ^2,*, Ethan G. Arnault³, Martin V. Gustafsson⁴, Leonardo Ranzani ⁴, Madisen Holbrook ⁵, Yangchen He⁶, Kenji Watanabe ⁷ et al.

Takashi Taniguchi ⁸, Daniel Rhodes^6,9, Vasili Perebeinos ¹⁰, James Hone ¹, and Kin Chung Fong ^4,†,‡

¹Department of Mechanical Engineering, Columbia University, New York, New York 10027, USA
²Department of Applied Physics and Mathematics, Columbia University, New York, New York 10027, USA
³Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
⁴RTX BBN Technologies, Quantum Engineering and Computing Group, Cambridge, Massachusetts 02138, USA
⁵Department of Physics, Columbia University, New York, New York 10027, USA
⁶Department of Materials Science and Engineering, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA
⁷Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
⁸Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
⁹Department of Physics, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA
¹⁰Department of Electrical Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260, USA

^*These authors contributed equally to this work.
^†Present address: Northeastern University.
^‡Contact author: k.fong@northeastern.edu

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Phys. Rev. Applied 24, 034016 – Published 5 September, 2025

DOI: https://doi.org/10.1103/3ssz-jjt6

Abstract

The narrow band gaps of semiconductors allow 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.

Physical Review Applied

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Crystalline superconductor-semiconductor Josephson junctions for compact superconducting qubits

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