Right-sizing fluxonium against charge noise

We analyze the charge-noise induced coherence time T2 of the fluxonium qubit as a function of the number of array junctions in the device, N. The pure dephasing rate decreases with N, but we find that the relaxation rate increases, so T2 achieves an optimum as a function of N. This optimum can be much smaller than the number typically chosen in experiments, yielding a route to improved fluxonium coherence and simplified device fabrication at the same time.