Fast parametric two-gubit gates with suppressed residual interaction using a parity-violated superconducting qubit

  1. Atsushi Noguchi,
  2. Alto Osada,
  3. Shumpei Masuda,
  4. Shingo Kono,
  5. Kentaro Heya,
  6. Samuel Piotr Wolski,
  7. Hiroki Takahashi,
  8. Takanori Sugiyama,
  9. Dany Lachance-Quirion,
  10. and Yasunobu Nakamura
We demonstrate fast two-qubit gates using a parity-violated superconducting qubit consisting of a capacitively-shunted asymmetric Josephson-junction loop under a finite magnetic flux bias. The second-order nonlinearity manifesting in the qubit enables the interaction with a neighboring single-junction transmon qubit via first-order inter-qubit sideband transitions with Rabi frequencies up to 30~MHz. Simultaneously, the unwanted static longitudinal~(ZZ) interaction is eliminated with ac Stark shifts induced by a continuous microwave drive near-resonant to the sideband transitions. The average fidelities of the two-qubit gates are evaluated with randomized benchmarking as 0.967, 0.951, 0.956 for CZ, iSWAP and SWAP gates, respectively.
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