Merged element transmon qubit based on the vdW Josephson junction

Van der Waals (vdW) heterostructures are a promising material platform to create lumped-element superconducting quantum circuits. For example, transmon qubits with conventional Al-AlOx-Al Josephson junctions shunted by a NbSe₂-hBN-NbSe₂ parallel plate capacitor have exhibited coherence times up 25 us and at least a 100X reduction in their footprint compared to conventional Al transmon qubits [1,2]. Here, we explore an “All vdW qubit” by exploiting NbSe₂-thin hBN-NbSe₂ heterostructures that can serve both as a Josephson junction and the shunting capacitor of a transmon qubit. By controlling the thickness of hBN layer, we integrate the Josephson junction and the capacitor into a single heterostructure, referred to as a merged-element transmon qubit. In these devices, the electric field will be contained in low-loss hBN thin film. Additionally, the footprint of the qubit can be significantly reduced in this merged structure. To characterize these junctions, we measure their switching current as a function of hBN layer thickness. We also incorporated the vdW Josephson junction into our qubit design. This approach could open new avenues for enhancing coherence times and scalability in superconducting quantum circuits.

[1] Wang, J.IJ., Yamoah, M.A., Li, Q. et al. Hexagonal boron nitride as a low-loss dielectric for superconducting quantum circuits and qubits. Nat. Mater. 21, 398–403 (2022).

[2] Antony, A. et al. Miniaturizing Transmon Qubits Using van der Waals Materials. Nano Letters 21, 10122-10126 (2021).