Sainan Huai

Tantalum airbridges for scalable superconducting quantum processors

  1. Kunliang Bu,
  2. Sainan Huai,
  3. Zhenxing Zhang,
  4. Dengfeng Li,
  5. Yuan Li,
  6. Jingjing Hu,
  7. Xiaopei Yang,
  8. Maochun Dai,
  9. Tianqi Cai,
  10. Yi-Cong Zheng,
  11. and Shengyu Zhang
The unique property of tantalum (Ta), particularly its long coherent lifetime in superconducting qubits and its exceptional resistance to both acid and alkali, makes it promising for
superconducting quantum processors. It is a notable advantage to achieve high-performance quantum processors with neat and unified fabrication of all circuit elements, including coplanar waveguides (CPW), qubits, and airbridges, on the tantalum film-based platform. Here, we propose a reliable tantalum airbridges with separate or fully-capped structure fabricated via a novel lift-off method, where a barrier layer with aluminium (Al) film is first introduced to separate two layers of photoresist and then etched away before the deposition of tantalum film, followed by cleaning with piranha solution to remove the residual photoresist on the chip. We characterize such tantalum airbridges as the control line jumpers, the ground plane crossovers and even coupling elements. They exhibit excellent connectivity, minimal capacitive loss, effectively suppress microwave and flux crosstalk and offer high freedom of coupling. Besides, by presenting a surface-13 tunable coupling superconducting quantum processor with median T1 reaching above 100 μs, the overall adaptability of tantalum airbridges is verified. The median single-qubit gate fidelity shows a tiny decrease from about 99.95% for the isolated Randomized Benchmarking to 99.94% for the simultaneous one. This fabrication method, compatible with all known superconducting materials, requires mild conditions of film deposition compared with the commonly used etching and grayscale lithography. Meanwhile, the experimental achievement of non-local coupling with controlled-Z (CZ) gate fidelity exceeding 99.2% may further facilitate qLDPC codes, laying a foundation for scalable quantum computation and quantum error correction with entirely tantalum elements.
arxiv pdf

Rapid and Unconditional Parametric Reset Protocol for Tunable Superconducting Qubits

  1. Yu Zhou,
  2. Zhenxing Zhang,
  3. Zelong Yin,
  4. Sainan Huai,
  5. Xiu Gu,
  6. Xiong Xu,
  7. Jonathan Allcock,
  8. Fuming Liu,
  9. Guanglei Xi,
  10. Qiaonian Yu,
  11. Hualiang Zhang,
  12. Mengyu Zhang,
  13. Hekang Li,
  14. Xiaohui Song,
  15. Zhan Wang,
  16. Dongning Zheng,
  17. Shuoming An,
  18. Yarui Zheng,
  19. and Shengyu Zhang
Qubit initialization is critical for many quantum algorithms and error correction schemes, and extensive efforts have been made to achieve this with high speed and efficiency. Here
we experimentally demonstrate a fast and high fidelity reset scheme for tunable superconducting qubits. A rapid decay channel is constructed by modulating the flux through a transmon qubit and realizing a swap between the qubit and its readout resonator. The residual excited population can be suppressed to 0.08% ± 0.08% within 34 ns, and the scheme requires no additional chip architecture, projective measurements, or feedback loops. In addition, the scheme has negligible effects on neighboring qubits, and is therefore suitable for large-scale multi-qubit systems. Our method also offers a way of entangling the qubit state with an itinerant single photon, particularly useful in quantum communication and quantum network applications.
arxiv pdf