Engineering Framework for Optimizing Superconducting Qubit Designs

Superconducting quantum technologies require qubit systems whose properties meet several often conflicting requirements, such as long coherence times and high anharmonicity. Here, we provide an engineering framework based on a generalized superconducting qubit model in the flux regime, which abstracts multiple circuit design parameters and thereby supports design optimization across multiple qubit properties. We experimentally investigate a special parameter regime which has both high anharmonicity ($\sim \text{\hspace{0.17em}⁣}1$GHz) and long quantum coherence times ($T_1\text{\hspace{0.17em}⁣}=\text{\hspace{0.17em}⁣}40\text{\hspace{0.17em}⁣}-\text{\hspace{0.17em}⁣}80\mu \mathrm{s}$ and $T_{2\mathrm{E}\mathrm{c}\mathrm{h}\mathrm{o}}\text{\hspace{0.17em}⁣}=\text{\hspace{0.17em}⁣}2T_1$).