Xuan Zhang

Characterization and Optimization of Tunable Couplers via Adiabatic Control in Superconducting Circuits

  1. Xuan Zhang,
  2. Xu Zhang,
  3. Changling Chen,
  4. Kai Tang,
  5. Kangyuan Yi,
  6. Kai Luo,
  7. Zheshu Xie,
  8. Yuanzhen Chen,
  9. and Tongxing Yan
In the pursuit of scalable superconducting quantum computing, tunable couplers have emerged as a pivotal component, offering the flexibility required for complex quantum operations
of high performance. In most current architectures of superconducting quantum chips, such couplers are not equipped with dedicated readout circuits to reduce complexity in both design and operation. However, this strategy poses challenges in precise characterization, calibration, and control of the couplers. In this work, we develop a hardware-efficient and robust technique based on adiabatic control to address the above issue. The critical ingredient of this technique is adiabatic swap (aSWAP) operation between a tunable coupler and nearby qubits. Using this technique, we have characterized and calibrated tunable couplers in our chips and achieved straightforward and precise control over these couplers. For example, we have demonstrated the calibration and correction of the flux distortion of couplers. In addition, we have also expanded this technique to tune the dispersive shift between a frequency-fixed qubit and its readout resonator over a wide range.
arxiv pdf

Hardware-Efficient Stabilization of Entanglement via Engineered Dissipation in Superconducting Circuits

  1. Changling Chen,
  2. Kai Tang,
  3. Yuxuan Zhou,
  4. KangYuan Yi,
  5. Xuan Zhang,
  6. Xu Zhang,
  7. Haosheng Guo,
  8. Song Liu,
  9. Yuanzhen Chen,
  10. Tongxing Yan,
  11. and Dapeng Yu
Generation and preservation of quantum entanglement are among the primary tasks in quantum information processing. State stabilization via quantum bath engineering offers a resource-efficient
approach to achieve this objective. However, current methods for engineering dissipative channels to stabilize target entangled states often require specialized hardware designs, complicating experimental realization and hindering their compatibility with scalable quantum computation architectures. In this work, we propose and experimentally demonstrate a stabilization protocol readily implementable in the mainstream integrated superconducting quantum circuits. The approach utilizes a Raman process involving a resonant (or nearly resonant) superconducting qubit array and their dedicated readout resonators to effectively emerge nonlocal dissipative channels. Leveraging individual controllability of the qubits and resonators, the protocol stabilizes two-qubit Bell states with a fidelity of 90.7%, marking the highest reported value in solid-state platforms to date. Furthermore, by extending this strategy to include three qubits, an entangled W state is achieved with a fidelity of 86.2%, which has not been experimentally investigated before. Notably, the protocol is of practical interest since it only utilizes existing hardware common to standard operations in the underlying superconducting circuits, thereby facilitating the exploration of many-body quantum entanglement with dissipative resources.
arxiv pdf