Alto Osada

All-microwave manipulation of superconducting qubits with a fixed-frequency transmon coupler

  1. Shotaro Shirai,
  2. Yuta Okubo,
  3. Kohei Matsuura,
  4. Alto Osada,
  5. Yasunobu Nakamura,
  6. and Atsushi Noguchi
All-microwave control of fixed-frequency superconducting quantum computing circuits is advantageous for minimizing the noise channels and wiring costs. Here we introduce a swap interaction
between two data transmons assisted by the third-order nonlinearity of a coupler transmon under a microwave drive. We model the interaction analytically and numerically and use it to implement an all-microwave controlled-Z gate. The gate based on the coupler-assisted swap transition maintains high drive efficiency and small residual interaction over a wide range of detuning between the data transmons.
arxiv pdf

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.
arxiv pdf