@article{204436,
  author = {Helin Zhang and Chunyang Ding and DK Weiss and Ziwen Huang and Yumei Ma and Charles Guinn and Sara Sussman and Sai Chitta and Danyang Chen and Andrew A. Houck and Jens Koch and David I. Schuster},
  title = {Tunable Inductive Coupler for High-Fidelity Gates between Fluxonium Qubits},
  abstract = {<p>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 𝑋⁢𝑋 coupling strengths (-35 to 75 MHz). The 𝑍⁢𝑍 coupling strength is \&lt;3 kHz across the entire coupler bias range and \&lt;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 √𝑖⁢SWAP gate in 258 ns with fidelity 99.72\%, and by driving at the sum frequency of the two qubits, we achieve a √𝑏⁢SWAP 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 √𝑏⁢SWAP drift (2⁢𝜎) \&lt;0.02\% and √𝑖⁢SWAP drift \&lt;0.08\%.</p>},
  year = {2024},
  journal = {PRX Quantum},
  month = {05/2025},
  url = {https://journals.aps.org/prxquantum/abstract/10.1103/PRXQuantum.5.020326},
  language = {eng},
}