Tunable Inductive Coupler for High-Fidelity Gates between Fluxonium Qubits

Helin Zhang, Chunyang Ding, D. K. Weiss, Ziwen Huang, Yuwei Ma, Charles Guinn, Sara Sussman, Sai Pavan Chitta, Danyang Chen, Andrew A. Houck, Jens Koch, David I. Schuster

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


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%.

Original languageEnglish (US)
Article number020326
JournalPRX Quantum
Issue number2
StatePublished - Apr 2024

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • General Computer Science
  • Mathematical Physics
  • General Physics and Astronomy
  • Applied Mathematics
  • Electrical and Electronic Engineering


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