A tunable coupler for suppressing adjacent superconducting qubit coupling

  1. X. Li,
  2. T. Cai,
  3. H. Yan,
  4. Z. Wang,
  5. X. Pan,
  6. Y. Ma,
  7. W. Cai,
  8. J. Han,
  9. Z. Hua,
  10. X. Han,
  11. Y. Wu,
  12. H. Zhang,
  13. H. Wang,
  14. Yipu Song,
  15. Luming Duan,
  16. and Luyan Sun
Controllable interaction between superconducting qubits is desirable for large-scale quantum computation and simulation. Here, based on a theoretical proposal by Yan et al. [Phys. Rev. Appl. 10, 054061 (2018)] we experimentally demonstrate a simply-designed and flux-controlled tunable coupler with continuous tunability by adjusting the coupler frequency, which can completely turn off adjacent superconducting qubit coupling. Utilizing the tunable interaction between two qubits via the coupler, we implement a controlled-phase (CZ) gate by tuning one qubit frequency into and out of the usual operating point while dynamically keeping the qubit-qubit coupling off. This scheme not only efficiently suppresses the leakage out of the computational subspace but also allows for the acquired two-qubit phase being geometric at the operating point only where the coupling is on. We achieve an average CZ gate fidelity of 98.3%, which is dominantly limited by qubit decoherence. The demonstrated tunable coupler provides a desirable tool to suppress adjacent qubit coupling and is suitable for large-scale quantum computation and simulation.
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