High-Coherence Fluxonium Qubit

We report superconducting fluxonium qubits with coherence times largely limited by energy relaxation and reproducibly satisfying T 2 > 100 μs (T 2 > 400 μs in one device).Moreover, given the state-of-the-art values of the surface loss tangent and the 1=f flux-noise amplitude, the coherence time can be further improved beyond 1 ms.Our results violate a common viewpoint that the number of Josephson junctions in a superconducting circuit-over 10 2 here-must be minimized for best qubit coherence.We outline how the unique to fluxonium combination of long coherence time and large anharmonicity can benefit both gate-based and adiabatic quantum computing.