Takanori Sugiyama

Fast readout and reset of a superconducting qubit coupled to a resonator with an intrinsic Purcell filter

  1. Yoshiki Sunada,
  2. Shingo Kono,
  3. Jesper Ilves,
  4. Shuhei Tamate,
  5. Takanori Sugiyama,
  6. Yutaka Tabuchi,
  7. and Yasunobu Nakamura
Coupling a resonator to a superconducting qubit enables various operations on the qubit including dispersive readout and unconditional reset. The speed of these operations is limited
by the external decay rate of the resonator. However, increasing the decay rate also increases the rate of qubit decay via the resonator, limiting the qubit lifetime. Here, we demonstrate that the resonator-mediated qubit decay can be suppressed by utilizing the distributed-element, multi-mode nature of the resonator. We show that the suppression exceeds two orders of magnitude over a bandwidth of 600 MHz. We use this „intrinsic Purcell filter“ to demonstrate a 40-ns readout with 99.1% fidelity and a 100-ns reset with residual excitation of less than 1.7%.
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