Novel two-qubit gates for the light fluxonium qubit*

The fluxonium qubit, taken in the light regime where phase-slip rate/energy is of the order of the inductive energy, presents a low-energy spectrum with reduced flux dispersion. With flux noise amplitude being weaker than that of charge noise, the light fluxonium qubit should benefit from a high coherence time without having to pay the price of a lower anharmonicity as it is the case of the transmon. Here, we introduce a two-qubit gate for the light fluxonium in a parameter regime where the coherence times are predicted to be long and that is within the reach of current circuit-QED technology. Our proposal exploits an analogy between flux- and charge-noise insensitive circuit modes [Pechenezhskiy et al., Nature 585, 368–371 (2020)] alongside lessons learned from the transmon qubit.