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We will be having CMJC this Friday, May 10th at 4pm, in the TIQM room (B421). Aurelia Brook will present:

Vertical Josephson Junctions in Thin Films and 2D VdW Devices

Transmon qubit architectures have long been the industry standard for implementing superconducting quantum computers. The standard transmon device consists of a Josephson Junction, a nonlinear inductor, and a capacitor to form a nonlinear LC circuit coupled to a readout resonator. As it is desirable to have more working qubits, we begin to encounter the issue of scale. The average transmon device is around 300 - 500 μm. Thus it has been proposed [1] that one could decrease the size of transmon devices by 2 orders of magnitude simply by vertically stacking the material used in Josephson Junctions and increasing the size of the tunnel barrier within the super-semi heterostructures, thereby utilizing the inherent capacitance of the materials instead of adding on large external shunt capacitors. In this work, I’ll go over initial results in implementing these Merged-Element Transmon (mergemon) devices using III-V systems, which showed issues with dielectric loss due to the comparatively larger dependence on having clean interfaces. I will then be presenting my own results [2, 3] in growing and characterizing novel candidate materials for use in these vertical Josephson Junctions, followed by some speculative looks into recent reports on implementing mergemon designs using 2D VdW materials [4, 5]. While the latter have not been formally published, 2D mergemons and epitaxially grown thin film mergemons show a promising new avenue for realizing cryogenic electronics and investigating quantum computation.

[1] Zhao, Ruichen, et al. “Merged-element transmon.” Physical Review Applied 14.6 (2020): 064006.

[2] Strohbeen, Patrick J., et al. “Superconductivity in hyperdoped Ge by molecular beam epitaxy.” AIP Advances 13.8 (2023).

[3] Strohbeen, Patrick J., et al. “Molecular beam epitaxy growth of superconducting tantalum germanide.” Applied Physics Letters 124.9 (2024).

[4] Lyons, John, et al. “Hybrid 2D-3D Heterostructures for Merged Element Transmons.” Bulletin of the American Physical Society (2024).

[5] Balgley, Jesse, et al. “Van der Waals materials based superconducting qubits.” Bulletin of the American Physical Society (2024).