Yasunari Suzuki

QuBE/Qubex: an integrated hardware-software system for superconducting qubit experiments with broadband control

  1. Akinori Machino,
  2. Kazuhisa Ogawa,
  3. Takefumi Miyoshi,
  4. Hidehisa Shiomi,
  5. Shinichi Morisaka,
  6. Ryo Matsuda,
  7. Nilton F. G. Filho,
  8. Koichiro Ban,
  9. Takafumi Miyanaga,
  10. Keisuke Koike,
  11. Ryutaro Ohira,
  12. Toshi Sumida,
  13. Yoshinori Kurimoto,
  14. Yuuya Sugita,
  15. Yosuke Ito,
  16. Yasunari Suzuki,
  17. Peter A. Spring,
  18. Shiyu Wang,
  19. Hiroto Mukai,
  20. Arvind Mamgain,
  21. Shuhei Tamate,
  22. Yutaka Tabuchi,
  23. Yasunobu Nakamura,
  24. and Makoto Negoro
Achieving high-fidelity operation in large-scale superconducting qubit systems requires not only control hardware with broad frequency coverage, low crosstalk, and tight synchronization
but also software that coordinates system configuration, experiment execution, and data analysis. Here we present an integrated qubit-control system that combines broadband microwave hardware with a pulse-level software stack for scalable superconducting qubit experiments. The hardware provides broadband microwave coverage, including an instantaneous span of up to 1.6 GHz from a control output, while the software reduces setup and calibration overhead through automated configuration and built-in experiment workflows. We validate the system on a 64-qubit fixed-frequency transmon chip through full-chip frequency identification and representative demonstrations, including multi-unit far-detuned cross-resonance calibration and benchmarking that yields a measured two-qubit gate fidelity of 98.34%, and multilevel readout beyond the computational subspace. By disclosing the hardware architecture and releasing the software stack as open source, this work provides an inspectable hardware-software foundation for scalable superconducting qubit control experiments.
arxiv pdf

Variational Quantum Gate Optimization

  1. Kentaro Heya,
  2. Yasunari Suzuki,
  3. Yasunobu Nakamura,
  4. and Keisuke Fujii
We propose a gate optimization method, which we call variational quantum gate optimization (VQGO). VQGO is a method to construct a target multi-qubit gate by optimizing a parametrized
quantum circuit which consists of tunable single-qubit gates with high fidelities and fixed multi-qubit gates with limited controlabilities. As an example, we apply the proposed scheme to the models relevant to superconducting qubit systems. We show in numerical simulations that the high-fidelity CNOT gate can be constructed with VQGO using cross-resonance gates with finite crosstalk. We also demonstrate that fast and a high-fidelity four-qubit syndrome extraction can be implemented with simultaneous cross-resonance drives even in the presence of non-commutative crosstalk. VQGO gives a pathway for designing efficient gate operations for quantum computers.
arxiv pdf