A Control Line Multiplexing Framework for Scalable Quantum Computing

  1. Dayu Li,
  2. Naibin Zhou,
  3. Zhiyuan Chen,
  4. Zihua Chen,
  5. Yu Xu,
  6. Yuan Li,
  7. Daojin Fan,
  8. Wenhao Chu,
  9. Xiawei Chen,
  10. Hui Deng,
  11. Jiacheng Gui,
  12. Linyin Hong,
  13. Bo Fan,
  14. Weiping Lin,
  15. Haonan Zou,
  16. Haoxin Lou,
  17. Xintao Zhao,
  18. Sirui Cao,
  19. Ying Chong,
  20. Qingling Zhu,
  21. Chen Wang,
  22. Yisen Hu,
  23. Kaili Zhang,
  24. Feifan Su,
  25. Haibin Zhang,
  26. Jianghan Yin,
  27. Yajie Du,
  28. Yinan Jiang,
  29. Haoping Luo,
  30. Weifeng Yang,
  31. Jiafei Wang,
  32. Jin Lin,
  33. Futian Liang,
  34. Hao Rong,
  35. Kai Yan,
  36. Ming Gong,
  37. Jinjin Li,
  38. Maliang Liu,
  39. Cheng-Zhi Peng,
  40. Shaowei Li,
  41. Xiaobo Zhu,
  42. and Jian-Wei Pan
Universal fault-tolerant superconducting quantum computers are expected to require millions of physical qubits; yet extending the prevailing dedicated-control-line paradigm to this
scale would exceed the wiring density and cooling-power budget of dilution refrigerators. Microwave frequency-division multiplexing (FDM) revolutionized classical communications by enabling many independent channels to share common transmission infrastructure. Translating this principle to superconducting quantum control, however, requires an all-microwave architecture and experimental validation of frequency-multiplexed gate control. Recent work in quantum error correction has demonstrated microwave-based readout, single-qubit gates and leakage suppression, whereas two-qubit gates remain predominantly driven by unipolar pulses and thus constitute the missing element of an all-microwave architecture. Here, we propose a periodically extensible hybrid multiplexing framework in which all gate operations are frequency-division multiplexed using polychromatic microwave pulses and band-pass filters, thereby reducing the required control-line count by one to two orders of magnitude. In a 1:4 demonstration, we achieve average errors of (6.4±0.2)×10−3 for parallel FDM CZ gates and (10.6±0.2)×10−4 for parallel FDM XY(π/2) gates, without statistically significant multiplexing-induced degradation. Together with on-chip DC sources, this FDM-based gate-control scheme completes the last missing module in a scalable multiplexed-control architecture toward universal fault-tolerant quantum computing.

Tuning superinductors by quantum coherence effects for enhancing quantum computing

  1. Bo Fan,
  2. Abhisek Samanta,
  3. and Antonio M. García-García
Research on spatially inhomogeneous weakly-coupled superconductors has recently received a boost of interest because of the experimental observation of a dramatic enhancement of the
kinetic inductance with relatively low losses. Here, we study the kinetic inductance and the quality factor of a strongly-disordered weakly-coupled superconducting thin film. We employ a gauge-invariant random-phase approximation capable of describing collective excitations and other fluctuations. In line with the experimental findings, in the range of frequencies of interest, we have found that an exponential increase of the kinetic inductance with disorder coexists with a still large quality factor ∼105. More interestingly, on the metallic side of the superconductor-insulator transition, we have identified a range of frequencies and temperatures, well below the critical one, where quantum coherence effects induce a broad statistical distribution of the quality factor with an average value that increases with disorder. We expect these findings to further stimulate experimental research on the design and optimization of superinductors for a better performance and miniaturization of quantum devices such as qubits circuits and microwave detectors.