Jingjing Niu

Suppressing Coherent Two-Qubit Errors via Dynamical Decoupling

  1. Jiawei Qiu,
  2. Yuxuan Zhou,
  3. Chang-Kang Hu,
  4. Jiahao Yuan,
  5. Libo Zhang,
  6. Ji Chu,
  7. Wenhui Huang,
  8. Weiyang Liu,
  9. Kai Luo,
  10. Zhongchu Ni,
  11. Xianchuang Pan,
  12. Zhixuan Yang,
  13. Yimeng Zhang,
  14. Yuanzhen Chen,
  15. Xiu-Hao Deng,
  16. Ling Hu,
  17. Jian Li,
  18. Jingjing Niu,
  19. Yuan Xu,
  20. Tongxing Yan,
  21. Youpeng Zhong,
  22. Song Liu,
  23. Fei Yan,
  24. and Dapeng Yu
Scalable quantum information processing requires the ability to tune multi-qubit interactions. This makes the precise manipulation of quantum states particularly difficult for multi-qubit
interactions because tunability unavoidably introduces sensitivity to fluctuations in the tuned parameters, leading to erroneous multi-qubit gate operations. The performance of quantum algorithms may be severely compromised by coherent multi-qubit errors. It is therefore imperative to understand how these fluctuations affect multi-qubit interactions and, more importantly, to mitigate their influence. In this study, we demonstrate how to implement dynamical-decoupling techniques to suppress the two-qubit analogue of the dephasing on a superconducting quantum device featuring a compact tunable coupler, a trending technology that enables the fast manipulation of qubit–qubit interactions. The pure-dephasing time shows an up to ~14 times enhancement on average when using robust sequences. The results are in good agreement with the noise generated from room-temperature circuits. Our study further reveals the decohering processes associated with tunable couplers and establishes a framework to develop gates and sequences robust against two-qubit errors.
arxiv pdf

Simulation of Higher-Order Topological Phases and Related Topological Phase Transitions in a Superconducting Qubit

  1. Jingjing Niu,
  2. Tongxing Yan,
  3. Yuxuan Zhou,
  4. Ziyu Tao,
  5. Xiaole Li,
  6. Weiyang Liu,
  7. Libo Zhang,
  8. Song Liu,
  9. Zhongbo Yan,
  10. Yuanzhen Chen,
  11. and Dapeng Yu
Higher-order topological insulators (TIs) and superconductors (TSCs) give rise to new bulk and boundary physics, as well as new classes of topological phase transitions. While higher-order
TIs have been actively studied on many platforms, the experimental study of higher-order TSCs has thus far been greatly hindered due to the scarcity of material realizations. To advance the study of higher-order TSCs, in this work we carry out the simulation of a two-dimensional spinless second-order TSC belonging to the symmetry class D in a superconducting qubit. Owing to the great flexibility and controllability of the quantum simulator, we observe the realization of higher-order topology directly through the measurement of the pseudo-spin texture in momentum space of the bulk for the first time, in sharp contrast to previous experiments based on the detection of gapless boundary modes in real space. Also through the measurement of the evolution of pseudo-spin texture with parameters, we further observe novel topological phase transitions from the second-order TSC to the trivial superconductor, as well as to the first-order TSC with nonzero Chern number. Our work sheds new light on the study of higher-order topological phases and topological phase transitions.
arxiv pdf