State-of-the-art superconducting qubits rely on a limited set of thin-film materials. Expanding their materials palette can improve performance, extend operating regimes, and introduce new functionalities, but conventional thin-film fabrication hinders systematic exploration of new material combinations. Van der Waals (vdW) materials offer a highly modular crystalline platform that facilitates such exploration while enabling gate-tunability, higher-temperature operation, and compact qubit geometries. Yet it remains unknown whether a fully vdW superconducting qubit can support quantum coherence and what mechanisms dominate loss at both low and elevated temperatures in such a device. Here we demonstrate quantum-coherent merged-element transmons made entirely from vdW Josephson junctions. These first-generation, fully crystalline qubits achieve microsecond lifetimes in an ultra-compact footprint without external shunt capacitors. Energy relaxation measurements, together with microwave characterization of vdW capacitors, point to dielectric loss as the dominant relaxation channel up to hundreds of millikelvin. These results establish vdW materials as a viable platform for compact superconducting quantum devices.
@article{arxiv.2512.08059,
title = {Coherent and compact van der Waals transmon qubits},
author = {Jesse Balgley and Jinho Park and Xuanjing Chu and Jiru Liu and Madisen Holbrook and Kenji Watanabe and Takashi Taniguchi and Archana Kamal and Leonardo Ranzani and Martin V. Gustafsson and James Hone and Kin Chung Fong},
journal= {arXiv preprint arXiv:2512.08059},
year = {2025}
}