Chung-Ting Ke

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

Flux tunable graphene-based superconducting quantum circuits coupled to 3D cavity

  1. Kuei-Lin Chiu,
  2. Youyi Chang,
  3. Avishma J. Lasrado,
  4. Cheng-Han Lo,
  5. Yung-Hsiang Chen,
  6. Tao-Yi Hsu,
  7. Yen-Chih Chen,
  8. Yi-Chen Tsai,
  9. Samina,
  10. Yen-Hsiang Lin,
  11. and Chung-Ting Ke
Correlation between transmon and its composite Josephson junctions (JJ) plays an important role in designing new types of superconducting qubits based on quantum materials. It is desirable
to have a type of device that not only allows exploration for use in quantum information processing but also probing intrinsic properties in the composite JJs. Here, we construct a flux-tunable 3D transmon-type superconducting quantum circuit made of graphene as a proof-of-concept prototype device. This 3D transmon-type device not only enables coupling to 3D cavities for microwave probes but also permits DC transport measurements on the same device, providing useful connections between transmon properties and critical currents associated with JJ’s properties. We have demonstrated how flux-modulation in cavity frequency and DC critical current can be correlated under the influence of Fraunhofer pattern of JJs in an asymmetric SQUID. The correlation analysis was further extended to link the flux-modulated transmon properties, such as flux-tunability in qubit and cavity frequencies, with SQUID symmetry analysis based on DC measurements. Our study paves the way towards integrating novel materials for exploration of new types of quantum devices for future technology while probing underlying physics in the composite materials.
arxiv pdf