High-Coherence Fluxonium Qubit

We report superconducting fluxonium qubits with coherence times largely limited by energy relaxation and reproducibly satisfyingT2>100μs(T2>400μsin one device). Moreover, given the state-of-the-art values of the surface loss tangent and the1/fflux-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—over102here—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.