Fluxonium Steps up to the Plate

Abstract

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.

Excitation dynamics in inductively coupled fluxonium circuits

“…The effect of charge noise is reduced in transmons due to capacitative shunting, but transmons are far from perfect two-level systems due to their small anharmonicity. An alternative qubit that is still protected from the low-frequency charge noise but has no sacrifice in anharmonicity is the fluxonium qubit [19][20][21][22]. In addition to its long coherence, the fluxonium can be designed to have multiple strong connections with its neighbors via galvanic coupling [23].…”