Partial protection in superconducting qubits

In recent years, fluxonium has gained notoriety among the superconducting qubit community for exceptionally long coherence times and large anharmonicity -- both highly desirable properties when designing future quantum processors. Among fluxonium's distinguishing properties is the ability to engineer the spectrum and subsequently the protection of the qubit transition by tuning the relevant energy scale parameters. In this talk, I will discuss different fluxonium parameter regimes that offer device-level partial protection from the omnipresent sources of decoherence. First, I will discuss high coherence fluxonium qubits operated at low- (100-500 MHz) and high- (3-5 GHz) frequencies that have comparably the same protection yet an order of magnitude different transition frequency. Furthermore, the higher-frequency fluxonium, called integer fluxonium, has a rich 3-level structure that can be utilized as an erasure qubit. Finally, I will discuss blochnium qubits which consist of a small-area Josephson junction shunted by a maximal per-unit-length inductance with minimal stray capacitance; created by using innovative fabrication techniques that significantly reduce the parasitic capacitance previously associated with such large inductances. Interestingly, blochnium's flux dispersion of the qubit transition is reduced to about 100 MHz while transitions to non-computational states can be tuned in the usual few-GHz range. Such a unique spectrum eliminates flux-noise-induced dephasing while operating away from sweet spots allowing for flux-controlled logical gates.