Understanding the decoherence of fluxonium from an EJ-tunable device

The fluxonium qubit is known for high coherence when biased around its half flux quantum sweet spot. Here we report the intensive study of decoherence models of a fluxonium qubit with in situ tunability of its Josephson energy by varying the external fluxes. The dissipation of the fluxonium at the sweet spot ranging from 80 MHz to 2 GHz agrees with decoherence models including dielectric loss and 1/f flux noise with a crossover point. And the dephasing of the fluxonium also agrees with the model with a similar 1/f flux noise amplitude. This work further validates the decoherence models of fluxonium and paves the way for the optimization of the coherence time and high-fidelity operations.