  We present a tradeoff between leakage and pure dephasing errors for the
fluxonium circuit. We show that in the insulating regime, i.e., when the
persistent current flowing across the circuit is suppressed, the pure dephasing
rate decreases exponentially as the impedance of the circuit is increased. In
contrast to this exponential decrease, the qubit remains sufficiently
anharmonic so that gates times can still be short, allowing for significant
reduction in the computational error rates.
