Xiang Fu

Low-Loss, High-Coherence Airbridge Interconnects Fabricated by Single-Step Lithography

  1. Jibang Fu,
  2. Bo Ren,
  3. Jiandong Ouyang,
  4. Cong Li,
  5. Kechengqi Zhu,
  6. Yonggang Che,
  7. Xiang Fu,
  8. Shichuan Xue,
  9. Zhaohua Yang,
  10. Mingtang Deng,
  11. and Junjie Wu
Airbridges are essential for creating high-performance, low-parasitic interconnects in integrated circuits and quantum devices. Conventional multi-step fabrication methods hinder miniaturization
and introduce process-related defects. We report a simplified process for fabricating nanoscale airbridges using only a single electron-beam lithography step. By optimizing a multilayer resist stack with a triple-exposure-dose scheme and a thermal reflow step, we achieve smooth, suspended metallic bridges with sub-200-nm features that exhibit robust mechanical stability. Fabricated within a gradiometric SQUID design for superconducting transmon qubits, these airbridges introduce no measurable additional loss in the relaxation time T1, while enabling a 2.5-fold enhancement of the dephasing time T∗2. This efficient method offers a practical route toward integrating high-performance three-dimensional interconnects in advanced quantum and nano-electronic devices.
arxiv pdf

Telegraph flux noise induced beating Ramsey fringe in transmon qubits

  1. Zhi-Hao Wu,
  2. Ling-Xiao Lei,
  3. Xin-Fang Zhang,
  4. Shi-Chuan Xue,
  5. Shun Hu,
  6. Cong Li,
  7. Xiang Fu,
  8. Ping-Xing Chen,
  9. Kai Lu,
  10. Ming-Tang Deng,
  11. and Jun-Jie Wu
Ramsey oscillations typically exhibit an exponential decay envelope due to environmental noise. However, recent experiments have observed nonmonotonic Ramsey fringes characterized by
beating patterns, which deviate from the standard behavior. These beating patterns have primarily been attributed to charge-noise fluctuations. In this paper, we investigate the flux-noise origin of these nonmonotonic Ramsey fringes in frequency-tunable transmon qubits. We develop a random telegraph noise (RTN) model to simulate the impact of telegraph-like flux-noise sources on Ramsey oscillations. Our simulations demonstrate that strong flux-RTN sources can induce beating patterns in the Ramsey fringes, showing excellent agreement with experimental observations in transmon qubits influenced by electronic environment-induced flux-noise. Our findings provide valuable insights into the role of flux-noise in qubit decoherence and underscore the importance of considering flux-noise RTN when analyzing nonmonotonic Ramsey fringes.
arxiv pdf