Long coherence times, large anharmonicity and robust charge-noise insensitivity render fluxonium qubits an interesting alternative to transmons. Recent experiments have demonstrated record coherence times for low-frequency fluxonia. Here, we propose a galvanic-coupling scheme with flux-tunable XX coupling. To implement a high-fidelity entangling iSWAP gate, we modulate the strength of this coupling and devise variable-time identity gates to synchronize required single-qubit operations. Both types of gates are implemented using strong ac flux drives, lasting for only a few drive periods. We employ a theoretical framework capable of capturing qubit dynamics beyond the rotating-wave approximation (RWA) as required for such strong drives. We predict an open-system fidelity of F>0.999 for the iSWAP gate under realistic conditions.
@article{arxiv.2207.03971,
title = {Fast high-fidelity gates for galvanically-coupled fluxonium qubits using strong flux modulation},
author = {D. K. Weiss and Helin Zhang and Chunyang Ding and Yuwei Ma and David I. Schuster and Jens Koch},
journal= {arXiv preprint arXiv:2207.03971},
year = {2023}
}