Novel charging effects in the fluxonium qubit

The fluxonium circuit has recently emerged as an attractive qubit modality for building a fault-tolerant quantum computer. Because of the presence of an inductive shunt, the fluxonium qubit is insensitive to the dc value of the offset-charge bias, n_g. However, the impact of nonzero-frequency fluctuations of n_g is not fully charted in the literature. In this talk, we derive a convenient form of the fluxonium Hamiltonian that makes it easier to characterize the effects of a time-dependent offset-charge bias. Our fluxonium model reveals a new noise channel for fluxonium related to quasiparticles, and has implications for high-fidelity qubit control.