Along with coworkers from the Schuster lab at UChicago, we introduce a coupling scheme for low frequency fluxonium qubits that allows for high-fidelity entangling gates. 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.

The paper may be found here.