Fluxonium Qubit in a 3D Cavity: Design and Implementation

We describe the implementation of a fluxonium artificial atom [1] with improved coherence times. Our qubit is inductively coupled to a Josephson junction resonator on a sapphire substrate, placed inside a 3D copper cavity. The keystone of the fluxonium qubit is its superinductance, which consists of an array of 90 Josephson junctions. We describe superinductance design improvements [2] which effectively eliminate spurious phase-slips and raise the self-resonant modes of the superinductance well above the frequency of the qubit. Networks of Josephson junctions will be useful for designing custom symmetries in cQED Hamiltonians.\\[4pt] [1] Manucharyan et al., Science, 326 (2009)\\[0pt] [2] Masluk et al., Phys. Rev. Lett. 109 (2012)