Xudong Liao

Tunable Hybrid-Mode Coupler Enabling Strong Interactions between Transmons at Centimeter-Scale Distance

  1. Jianwen Xu,
  2. Xiang Deng,
  3. Wen Zheng,
  4. Wenchang Yan,
  5. Tao Zhang,
  6. Zhenchuan Zhang,
  7. Wanli Huang,
  8. Xiaoyu Xia,
  9. Xudong Liao,
  10. Yu Zhang,
  11. Jie Zhao,
  12. Shaoxiong Li,
  13. Xinsheng Tan,
  14. Dong Lan,
  15. and Yang Yu
The transmon, a fabrication-friendly superconducting qubit, remains a leading candidate for scalable quantum computing. Recent advances in tunable couplers have accelerated progress
toward high-performance quantum processors. However, extending coherent interactions beyond millimeter scales to enhance quantum connectivity presents a critical challenge. Here, we introduce a hybrid-mode coupler exploiting resonator-transmon hybridization to simultaneously engineer the two lowest-frequency mode, enabling high-contrast coupling between centimeter-scale transmons. For a 1-cm coupler, our framework predicts flux-tunable XX and ZZ coupling strengths reaching 23 MHz and 100 MHz, with modulation contrasts exceeding 102 and 104, respectively, demonstrating quantitative agreement with an effective two-channel model. This work provides an efficient pathway to mitigate the inherent connectivity constraints imposed by short-range interactions, enabling transmon-based architectures compatible with hardware-efficient quantum tasks.
arxiv pdf

Broadband merged-element Josephson parametric amplifier

  1. Yuting Sun,
  2. Xianke Li,
  3. Qingyu Wang,
  4. Tairong Bai,
  5. Xudong Liao,
  6. Dong Lan,
  7. Jie Zhao,
  8. and Yang Yu
Broadband quantum-limited amplifiers are essential for quantum information processing, yet challenges in design and fabrication continue to hinder their widespread applications. Here,
we introduce the broadband merged-element Josephson parametric amplifier in which the discrete parallel capacitor is directly integrated with the Josephson junctions. This merged-element design eliminates the shortcomings of discrete capacitors, simplifying the fabrication process, reducing the need for high-precision lithography tools, and ensuring compatibility with standard superconducting qubit fabrication procedures. Experimental results demonstrate a gain of 15 dB over a 500 MHz bandwidth, a mean saturation power of -116 dBm and near-quantum-limited noise performance. This robust readily implemented parametric amplifier holds significant promise for broader applications in superconducting quantum information and the advancement of quantum computation.
arxiv pdf