  Increasing the degree of control over physical qubits is a crucial component
of quantum computing research. We report a superconducting qubit of fluxonium
type with the Ramsey coherence time reaching $T_2^*= 1.48 \pm 0.13
\mathrm{~ms}$, which exceeds the state of the art value by an order of
magnitude. As a result, the average single-qubit gate fidelity grew above
$0.9999$, surpassing, to our knowledge, any other solid-state quantum system.
Furthermore, by measuring energy relaxation of the parity-forbidden transition
to second excited state, we exclude the effect of out-of-equilibrium
quasiparticles on coherence in our circuit. Combined with recent demonstrations
of two-qubit gates on fluxoniums, our result paves the way for the next
generation of quantum processors.
