The Most Coherent Superconducting Qubit?

We report superconducting fluxonium qubits with coherence times limited by energy relaxation and reproducibly satisfying T₂ > 100 μs (T₂ > 400 μs in one device). Moreover, given the state-of-the-art values of the surface loss tangent and 1/f flux noise amplitude, coherence times can be further improved beyond 1 ms. Our results violate a common viewpoint that the number of Josephson junctions in a superconducting circuit - over 10² here - must be minimized for the best qubit coherence. We outline how the combination of long coherence times and large anharmonicity unque to fluxonium can benefit both gate-based and adiabtic quantum computing.