The Merged Element Transmon

Abstract

The superconducting transmon qubit consists of a Josephson junction and a shunt capacitor, which together form a nonlinear resonant circuit. This basic concept allows for a variety of implementations. One such variation is the merged element transmon (MET), in which the Josephson junction is engineered to act as its own parallel shunt capacitor.[1,2] The MET offers a potentially smaller footprint and a very different electric field profile than conventional transmons. We have produced devices based on micrometer scale Al/AlOx/Al junctions which show surprisingly good T1 times given the relatively large junction size, with T1> 100 microseconds in some cases. Because the MET concentrates the energy in the junction, it may be possible to achieve even better coherence times and reduce the effect of two level systems by making more perfect dielectric barriers in the junction, for example by epitaxial means. For conventional small junction transmons, our results, combined with scaling arguments, suggest that the junction is not normally the dominant source of energy loss. [1]. R. Zhao, S. Park, T. Zhao, M. Bal, C.R.H. McRae, J. Long, and D.P. Pappas, Phys. Rev. Applied 14, 064006 (2020). [2] H.J. Mamin, E. Huang, S. Carnevale, C.T. Rettner, N. Arellano, M.H. Sherwood, C. Kurter, B. Trimm, M. Sandberg, R.M. Shelby, M.A. Mueed, B.A. Madon, A. Pushp, M. Steffen, and D. Rugar, Phys. Rev. Applied 16, 024023 (2021)