Xianke Li

Parametric Phase Modulation in Superconducting Circuits

  1. Zhuang Ma,
  2. Xianke Li,
  3. Hongyi Shi,
  4. Ruonan Guo,
  5. Jianwen Xu,
  6. Xinsheng Tan,
  7. and Yang Yu
Parametric modulation is widely employed in superconducting circuits for quantum simulations and high-fidelity two-qubit gates, valued for its versatility. Conventionally, the qubit
coupling strength is determined by the amplitude of the parametric flux pulse, which affects qubit parameters dramatically. In this article, we propose and implement a phase modulation scheme to tune the interaction strength via adjusting the relative phase between the parametric flux pulses applied to two coupled qubits. We characterize this modulation for sideband couplings, at both sweet and offsweet spots, achieving a broad range of coupling strengths as confirmed by both population dynamics and spectroscopy methods. This approach enables phase-controlled modulation of coupling strength, providing a promising candidate for parametrically driven quantum simulations and gate operations.
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