Two-Fluxonium Cross-Resonance Gate
Ebru Dogan, Dario Rosenstock, Loïck Le Guevel, Haonan Xiong, Raymond Mencia, Aaron Somoroff, Konstantin Nesterov, Maxim Vavilov, Vladimir Manucharyan, Chen Wang
Abstract
The superconducting fluxonium qubit has a great potential for high-fidelity quantum gates with its long coherence times and strong anharmonicity at the half-flux-quantum sweet spot. However, current implementations of two-qubit gates compromise fluxonium's coherence properties by requiring either a temporary population of the noncomputational states or tuning the magnetic flux off the sweet spot. Here we realize a fast all-microwave cross-resonance gate between two capacitively coupled fluxoniums with the qubit dynamics well confined to the computational space. We demonstrate a direct controlled not (cnot) gate in 70 ns with fidelity up to $\mathcal{F}=0.9949(6)$ despite the limitations of a suboptimal measurement setup and device coherence. Our results project a possible pathway towards reducing the two-qubit error rate near to or below ${10}^{\ensuremath{-}4}$ with present-day technologies.