Jing-Ning Zhang

Performing SU(d) operations and rudimentary algorithms in a superconducting transmon qudit for d=3 and d=4

  1. Pei Liu,
  2. Ruixia Wang,
  3. Jing-Ning Zhang,
  4. Yingshan Zhang,
  5. Xiaoxia Cai,
  6. Huikai Xu,
  7. Zhiyuan Li,
  8. Jiaxiu Han,
  9. Xuegang Li,
  10. Guangming Xue,
  11. Weiyang Liu,
  12. Li You,
  13. Yirong Jin,
  14. and Haifeng Yu
Quantum computation architecture based on d-level systems, or qudits, has attracted considerable attention recently due to their enlarged Hilbert space. Extensive theoretical and experimental
studies have addressed aspects of algorithms and benchmarking techniques for qudit-based quantum computation and quantum information processing. Here, we report a physical realization of qudit with upto 4 embedded levels in a superconducting transmon, demonstrating high-fidelity initialization, manipulation, and simultaneous multi-level readout. In addition to constructing SU(d) operations and benchmarking protocols for quantum state tomography, quantum process tomography, and randomized benchmarking etc, we experimentally carry out these operations for d=3 and d=4. Moreover, we perform prototypical quantum algorithms and observe outcomes consistent with expectations. Our work will hopefully stimulate further research interest in developing manipulation protocols and efficient applications for quantum processors with qudits.
arxiv pdf

Error per single-qubit gate below 10−4 in a superconducting qubit

  1. Zhiyuan Li,
  2. Pei Liu,
  3. Peng Zhao,
  4. Zhenyu Mi,
  5. Huikai Xu,
  6. Xuehui Liang,
  7. Tang Su,
  8. Weijie Sun,
  9. Guangming Xue,
  10. Jing-Ning Zhang,
  11. Weiyang Liu,
  12. Yirong Jin,
  13. and Haifeng Yu
Implementing arbitrary single-qubit gates with near perfect fidelity is among the most fundamental requirements in gate-based quantum information processing. In this work, we fabric
a transmon qubit with long coherence times and demonstrate single-qubit gates with the average gate error below 10−4, i.e. (7.42±0.04)×10−5 by randomized benchmarking (RB). To understand the error sources, we experimentally obtain an error budget, consisting of the decoherence errors lower bounded by (4.62±0.04)×10−5 and the leakage rate per gate of (1.16±0.04)×10−5. Moreover, we reconstruct the process matrices for the single-qubit gates by the gate set tomography (GST), with which we simulate RB sequences and obtain single-qubit fedlities consistent with experimental results. We also observe non-Markovian behavior in the experiment of long-sequence GST, which may provide guidance for further calibration. The demonstration extends the upper limit that the average fidelity of single-qubit gates can reach in a transmon-qubit system, and thus can be an essential step towards practical and reliable quantum computation in the near future.
arxiv pdf