Design of a granular aluminum fluxonium qubit in a coplanar waveguide architecture

Fluxonium qubits are often embedded in rectangular waveguides which dilute the electric field and favor high coherence [1,2]. However, this configuration complicates in-situ flux gates and multi-qubit experiments. Here, we present a fluxonium qubit placed in a coplanar waveguide architecture with an integrated fast-flux coil, surrounded by a normal metal ground plane. The superinductor is made out of granular aluminum (grAl) [3] and the use of a comparably large silver ground plane potentially decreases the number of quasiparticles in the system via phonon trapping [4].

[1] Pop et al., Nature 508, 369–372 (2014)

[2] Somoroff et al., arXiv:2103.08578 (2021)

[3] Grünhaupt and Spiecker et al., Nat. Mater. 18, 816–819 (2019)

[4] Henriques and Valenti et al., Appl. Phys. Lett. 115, 212601 (2019)