Stable CNOT-gate on inductively-coupled fluxonium qubits with over 99.9% fidelity
Fluxonium qubit is a promising elementary building block for quantum information processing due to its long coherence time combined with a strong anharmonicity. In this work, we realize a 60 ns direct CNOT-gate on two inductively-coupled fluxoniums, which behave almost exactly as a pair of transversely-coupled spin-1/2 systems. In particular, the generally unwanted static ZZ-term resulting from the non-computational transitions is nearly absent, even with a strong qubit-qubit hybridization. The CNOT-gate fidelity, estimated using randomized benchmarking, was as high as 99.94%. Furthermore, the fidelity remains above 99.9% for 24 days without any recalibration between measurements. Compared with the 99.96% fidelity of a 60 ns identity gate, our data brings the investigation of the non-decoherence-related errors during logical operations down to 2×10-4. The present result adds a simple and robust two-qubit gate into the still relatively small family of the “beyond three nines” gates on superconducting qubits.
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