Fanming Qu

Read out the fermion parity of a potential artificial Kitaev chain utilizing a transmon qubit

  1. Enna Zhuo,
  2. Xiaozhou Yang,
  3. Yuyang Huang,
  4. Zhaozheng Lyu,
  5. Ang Li,
  6. Bing Li,
  7. Yunxiao Zhang,
  8. Xiang Wang,
  9. Duolin Wang,
  10. Yukun Shi,
  11. Anqi Wang,
  12. E. P. A. M. Bakkers,
  13. Xiaodong Han,
  14. Xiaohui Song,
  15. Peiling Li,
  16. Bingbing Tong,
  17. Ziwei Dou,
  18. Guangtong Liu,
  19. Fanming Qu,
  20. Jie Shen,
  21. and Li Lu
Artificial Kitaev chains have emerged as a promising platform for realizing topological quantum computing. Once the chains are formed and the Majorana zero modes are braided/fused,
reading out the parity of the chains is essential for further verifying the non-Abelian property of the Majorana zero modes. Here we demonstrate the feasibility of using a superconducting transmon qubit, which incorporates an end of a four-site quantum dot-superconductor chain based on a Ge/Si nanowire, to directly detect the singlet/doublet state, and thus the parity of the entire chain. We also demonstrate that for multiple-dot chains there are two types of 0-{\pi} transitions between different charging states: the parity-flip 0-{\pi} transition and the parity-preserved 0-{\pi} transition. Furthermore, we show that the inter-dot coupling, hence the strengths of cross Andreev reflection and elastic cotunneling of electrons, can be adjusted by local electrostatic gating in chains fabricated on Ge/Si core-shell nanowires. Our exploration would be helpful for the ultimate realization of topological quantum computing based on artificial Kitaev chains.
arxiv pdf

Homointerface planar Josephson junction based on inverse proximity effect

  1. Juewen Fan,
  2. Bingyan Jiang,
  3. Jiaji Zhao,
  4. Ran Bi,
  5. Jiadong Zhou,
  6. Zheng Liu,
  7. Ning Kang,
  8. Fanming Qu,
  9. Li Lu,
  10. and Xiaosong Wu
The quality of a superconductor-normal metal-superconductor (SNS) Josephson junction (JJ) depends crucially on the transparency of the superconductor-normal metal (S/N) interface. We
demonstrate a technique for fabricating planar JJs with perfect interfaces. The technique utilizes a strong inverse proximity effect (IPE) discovered in Al/V5S8 bilayers, by which Al is driven into the normal state. The highly transparent homointerface enables the flow of Josephson supercurrent across a 2.9 μm long weak link. Moreover, our JJ exhibits a giant critical current and a large product of the critical current and the normal state resistance. The latter exceeds the theoretical bound, which is probably related to the unusual normal metal weak link.
arxiv pdf