Tunable Inductive Coupler for High-Fidelity Gates Between Fluxonium Qubits
Helin Zhang, Chunyang Ding, Daniel Weiss, Ziwen Huang, Yuwei Ma, Charles Guinn, Sara Sussman, Sai Pavan Chitta, Danyang Chen, Andrew Houck, Jens Koch, David Schuster · PRX Quantum · 2024
The fluxonium qubit is a promising candidate for quantum computation due to its long coherence times and large anharmonicity. We present a tunable coupler that realizes strong inductive coupling between two heavy-fluxonium qubits, each with approximately 50 -MHz frequencies and approximately 5 -GHz anharmonicities. The coupler enables the qubits to have a large tuning range of XX coupling strengths ( −35 to 75 MHz). The ZZ coupling strength is <3 kHz across the entire coupler bias range and <100 Hz at the coupler off position. These qualities lead to fast high-fidelity single- and two-qubit gates. By driving at the difference frequency of the two qubits, we realize a iSWAP gate in 258 ns with fidelity 99.72%, and by driving at the sum frequency of the two qubits, we achieve a bSWAP gate in 102 ns with fidelity 99.91%. This latter gate is only five qubit Larmor periods in length. We run cross-entropy benchmarking for over 20 consecutive hours and measure stable gate fidelities, with bSWAP drift ( 2σ ) <0.02% and iSWAP drift <0.08% . Published by the American Physical Society 2024