Xiuhao Deng

Low-loss interconnects for modular superconducting quantum processors

  1. Jingjing Niu,
  2. Libo Zhang,
  3. Yang Liu,
  4. Jiawei Qiu,
  5. Wenhui Huang,
  6. Jiaxiang Huang,
  7. Hao Jia,
  8. Jiawei Liu,
  9. Ziyu Tao,
  10. Weiwei Wei,
  11. Yuxuan Zhou,
  12. Wanjing Zou,
  13. Yuanzhen Chen,
  14. Xiaowei Deng,
  15. Xiuhao Deng,
  16. Changkang Hu,
  17. Ling Hu,
  18. Jian Li,
  19. Dian Tan,
  20. Yuan Xu,
  21. Fei Yan,
  22. Tongxing Yan,
  23. Song Liu,
  24. Youpeng Zhong,
  25. Andrew N. Cleland,
  26. and Dapeng Yu
Scaling is now a key challenge in superconducting quantum computing. One solution is to build modular systems in which smaller-scale quantum modules are individually constructed and
calibrated, and then assembled into a larger architecture. This, however, requires the development of suitable interconnects. Here, we report low-loss interconnects based on pure aluminium coaxial cables and on-chip impedance transformers featuring quality factors up to 8.1×105, which is comparable to the performance of our transmon qubits fabricated on single-crystal sapphire substrate. We use these interconnects to link five quantum modules with inter-module quantum state transfer and Bell state fidelities up to 99\%. To benchmark the overall performance of the processor, we create maximally-entangled, multi-qubit Greenberger-Horne-Zeilinger (GHZ) states. The generated inter-module four-qubit GHZ state exhibits 92.0\% fidelity. We also entangle up to 12 qubits in a GHZ state with 55.8±1.8% fidelity, which is above the genuine multipartite entanglement threshold of 1/2. These results represent a viable modular approach for large-scale superconducting quantum processors.
arxiv pdf

Scalable method for eliminating residual ZZ interaction between superconducting qubits

  1. Zhongchu Ni,
  2. Sai Li,
  3. Libo Zhang,
  4. Ji Chu,
  5. Jingjing Niu,
  6. Tongxing Yan,
  7. Xiuhao Deng,
  8. Ling Hu,
  9. Jian Li,
  10. Youpeng Zhong,
  11. Song Liu,
  12. Fei Yan,
  13. Yuan Xu,
  14. and Dapeng Yu
Unwanted ZZ interaction is a quantum-mechanical crosstalk phenomenon which correlates qubit dynamics and is ubiquitous in superconducting qubit system. It adversely affects the quality
of quantum operations and can be detrimental in scalable quantum information processing. Here we propose and experimentally demonstrate a practically extensible approach for complete cancellation of residual ZZ interaction between fixed-frequency transmon qubits, which are known for long coherence and simple control. We apply to the intermediate coupler that connects the qubits a weak microwave drive at a properly chosen frequency in order to noninvasively induce ac Stark shift for ZZ cancellation. We verify the cancellation performance by measuring vanishing two-qubit entangling phases and ZZ correlations. In addition, we implement randomized benchmarking experiment to extract the idling gate fidelity which shows good agreement with the coherence limit, demonstrating the effectiveness of ZZ cancellation. Our method allows independent addressability of each qubit-qubit connection, and is applicable to both non-tunable and tunable coupler, promising better compatibility with future large-scale quantum processors.
arxiv pdf

Site-wise manipulations and Mott insulator-superfluid transition of interacting photons using superconducting circuit simulators

  1. Xiuhao Deng,
  2. Chunjing Jia,
  3. and Chih-Chun Chien
The Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in many-body physics, and it exhibits a Mott insulator (MI)-superfluid (SF) transition at integer
filling. Here a quantum simulator of the BHM using a superconducting circuit is proposed. Specifically, a superconducting transmission line resonator supporting microwave photons is coupled to a charge qubit to form one site of the BHM, and adjacent sites are connected by a tunable coupler. To obtain a mapping from the superconducting circuit to the BHM, we focus on the dispersive regime where the excitations remain photon-like. Standard perturbation theory is implemented to locate the parameter range where the MI-SF transition may be simulated. This simulator allows single-site manipulations and we illustrate this feature by considering two scenarios where a single-site manipulation can drive a MI-SF transition. The transition can be analyzed by mean-field analyses, and the exact diagonalization was implemented to provide accurate results. The variance of the photon density and the fidelity metric clearly show signatures of the transition. Experimental realizations and other possible applications of this simulator are also discussed.
arxiv pdf

Parametric four-wave mixing toolbox for superconducting resonators

  1. A. V. Sharypov,
  2. Xiuhao Deng,
  3. and Lin Tian
We study a superconducting circuit that can act as a toolbox to generate various Bogoliubov-linear and nonlinear quantum operations on the microwave photon modes of superconducting
resonators within one single circuit. The quantum operations are generated by exploring dispersive four-wave mixing (FWM) processes involving the resonator modes. Different FWM geometries can be realized by adjusting the circuit parameters and by applying appropriate microwave drivings. We illustrate this scheme using a circuit made of two superconducting qubits that couple with each other. Each qubit couples with one superconducting resonator. We also discuss main quantum errors in this scheme and study the fidelity of the quantum operations by numerical simulation. Our scheme provides a practical approach to realize quantum information protocols on superconducting resonators.
arxiv pdf