Crystalline superconductor-semiconductor Josephson junctions for compact superconducting qubits

In the last decade, hybrid superconductor-semiconductor systems have enabled novel quantum devices by leveraging the versatile electronic properties of semiconductors. Van der Waals materials, with their crystalline structure, ordered interfaces, and exceptional electronic properties, present an ideal yet relatively unexplored platform to mitigate loss and shrink circuit footprints. We characterize the DC electronic properties of crystalline vertical Josephson junctions made of van der Waals superconductor NbSe₂ electrodes and semiconductor WSe₂ weak links. These junctions exhibit Josephson coupling across WSe₂ as thick as 12 nm (18 atomic layers), with six orders of magnitude variability in junction switching current density and normal-state-resistance–area product as a function of weak link thickness. Notably, as we increase this thickness, we observe a crossover from proximity-type to tunneling-type junction behavior. Using these trends, we design and achieve dispersive coupling between a prototype all-crystalline merged-element transmon and a microwave resonator, demonstrating the promise of crystalline materials for compact superconducting quantum devices.