Chii-Dong Chen

Scaffold-Assisted Window Junctions for Superconducting Qubit Fabrication

  1. Chung-Ting Ke,
  2. Jun-Yi Tsai,
  3. Yen-Chun Chen,
  4. Zhen-Wei Xu,
  5. Elam Blackwell,
  6. Matthew A. Snyder,
  7. Spencer Weeden,
  8. Peng-Sheng Chen,
  9. Chih-Ming Lai,
  10. Shyh-Shyuan Sheu,
  11. Zihao Yang,
  12. Cen-Shawn Wu,
  13. Alan Ho,
  14. R. McDermott,
  15. John Martinis,
  16. and Chii-Dong Chen
The superconducting qubit is one of the promising directions in realizing fault-tolerant quantum computing (FTQC), which requires many high-quality qubits. To achieve this, it is desirable
to leverage modern semiconductor industry technology to ensure quality, uniformity, and reproducibility. However, conventional Josephson junction fabrication relies mainly on resist-assistant double-angle evaporation, posing integration challenges. Here, we demonstrate a lift-off-free qubit fabrication that integrates seamlessly with existing industrial technologies. This method employs a silicon oxide (SiO2) scaffold to define an etched window with a well-controlled size to form a Josephson junction. The SiO2, which has a large dielectric loss, is etched away in the final step using vapor HF leaving little residue. This Window junction (WJ) process mitigates the degradation of qubit quality during fabrication and allows clean removal of the scaffold. The WJ process is validated by inspection and Josephson junction measurement. The scaffold removal process is verified by measuring the quality factor of the resonators. Furthermore, compared to scaffolds fabricated by plasma-enhanced chemical vapor deposition (PECVD), qubits made by WJ through physical vapor deposition (PVD) achieve relaxation time up to 57μs. Our results pave the way for a lift-off-free qubit fabrication process, designed to be compatible with modern foundry tools and capable of minimizing damage to the substrate and material surfaces.
arxiv pdf

Slow and Stored Light via Electromagnetically Induced Transparency Using A Λ-type Superconducting Artificial Atom

  1. Kai-I Chu,
  2. Xiao-Cheng Lu,
  3. Kuan-Hsun Chiang,
  4. Yen-Hsiang Lin,
  5. Chii-Dong Chen,
  6. Ite A. Yu,
  7. Wen-Te Liao,
  8. and Yung-Fu Chen
Recent progresses in Josephson-junction-based superconducting circuits have propelled quantum information processing forward. However, the lack of a metastable state in most superconducting
artificial atoms hinders the development of photonic quantum memory in this platform. Here, we use a single superconducting qubit-resonator system to realize a desired Λ-type artificial atom, and to demonstrate slow light with a group velocity of 3.6 km/s and the microwave storage with a memory time extending to several hundred nanoseconds via electromagnetically induced transparency. Our results highlight the potential of achieving microwave quantum memory, promising substantial advancements in quantum information processing within superconducting circuits.
arxiv pdf

Characterizing Low-Quality-Factor Dissipative Superconducting Resonators

  1. Yu-Cheng Chang,
  2. Bayan Karimi,
  3. Jorden Senior,
  4. Alberto Ronzani,
  5. Joonas T. Peltonen,
  6. Hsi-Sheng Goan,
  7. Chii-Dong Chen,
  8. and Jukka P. Pekola
Characterizing superconducting microwave resonators with highly dissipative elements is a technical challenge, but a requirement for implementing and understanding the operation of
hybrid quantum devices involving dissipative elements, e.g. for thermal engineering and detection. We present experiments on λ/4 superconducting niobium coplanar waveguide (CPW) resonators, shunted at the antinode by a dissipative copper microstrip via aluminium leads, yielding a quality factor unresolvable from the typical microwave environment. By measuring the transmission both above and below this transition, we are able to isolate the resonance. We then experimentally verify this method with copper microstrips of increasing thicknesses, from 50 nm to 150 nm, and measure quality factors in the range of 10∼67 in a consistent way.
arxiv pdf