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arXiv:2103.09163 · Physical Review Applied

Merged-Element Transmons: Design and Qubit Performance

H. Jonathon Mamin, Elbert Huang, Santino D. Carnevale, Charles T. Rettner, N. Arellano, Mark Sherwood, Cihan Kurter, Bryan Trimm, Martin Sandberg, Robert M. Shelby, M. A. Mueed, Benjamin Madon, Aakash Pushp, Matthias Steffen, D. Rugar

Published Aug 13, 2021• 57 citations
arXivHTMLPDF

Abstract

We demonstrate a superconducting transmon qubit in which a Josephson junction has been engineered to act as its own parallel shunt capacitor. This merged-element transmon potentially offers a smaller footprint than conventional transmons. Because it concentrates the electromagnetic energy inside the junction, it reduces the relative electric field participation from other interfaces. By combining micrometer-scale $\mathrm{Al}$/$\mathrm{Al}\mathrm{O}$${}_{x}$/$\mathrm{Al}$ junctions with long oxidations, we produce functional devices with ${E}_{J}/{E}_{C}$ in the low-transmon regime (${E}_{J}/{E}_{C}\ensuremath{\lesssim}30$). Cryogenic $I$-$V$ measurements show a sharp $dI/dV$ structure with low subgap conduction. Qubit spectroscopy of tunable versions shows a small number of avoided level crossings, suggesting the presence of two-level systems. We observe mean ${T}_{1}$ times typically in the range of $10--90\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{s}$, with some annealed devices exhibiting ${T}_{1}>100\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{s}$ over several hours. The results suggest that energy relaxation in conventional small-junction transmons is not limited by junction loss.

DOI
10.1103/physrevapplied.16.024023

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