Coherent and compact van der Waals transmon qubits

TL;DR

This paper demonstrates the first quantum-coherent superconducting transmon qubits made entirely from van der Waals materials, achieving microsecond lifetimes and highlighting dielectric loss as a key relaxation mechanism, thus establishing vdW materials as a promising platform.

Contribution

It introduces fully vdW superconducting qubits with high coherence and compact design, enabling systematic material exploration for quantum devices.

Findings

Achieved microsecond qubit lifetimes with vdW transmons.

Identified dielectric loss as the main relaxation channel.

Demonstrated operation up to hundreds of millikelvin.

Abstract

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.