Cupjin Huang

Fluxonium: an alternative qubit platform for high-fidelity operations

  1. Feng Bao,
  2. Hao Deng,
  3. Dawei Ding,
  4. Ran Gao,
  5. Xun Gao,
  6. Cupjin Huang,
  7. Xun Jiang,
  8. Hsiang-Sheng Ku,
  9. Zhisheng Li,
  10. Xizheng Ma,
  11. Xiaotong Ni,
  12. Jin Qin,
  13. Zhijun Song,
  14. Hantao Sun,
  15. Chengchun Tang,
  16. Tenghui Wang,
  17. Feng Wu,
  18. Tian Xia,
  19. Wenlong Yu,
  20. Fang Zhang,
  21. Gengyan Zhang,
  22. Xiaohang Zhang,
  23. Jingwei Zhou,
  24. Xing Zhu,
  25. Yaoyun Shi,
  26. Jianxin Chen,
  27. Hui-Hai Zhao,
  28. and Chunqing Deng
Superconducting qubits provide a promising path toward building large-scale quantum computers. The simple and robust transmon qubit has been the leading platform, achieving multiple
milestones. However, fault-tolerant quantum computing calls for qubit operations at error rates significantly lower than those exhibited in the state of the art. Consequently, alternative superconducting qubits with better error protection have attracted increasing interest. Among them, fluxonium is a particularly promising candidate, featuring large anharmonicity and long coherence times. Here, we engineer a fluxonium-based quantum processor that integrates high qubit-coherence, fast frequency-tunability, and individual-qubit addressability for reset, readout, and gates. With simple and fast gate schemes, we achieve an average single-qubit gate fidelity of 99.97% and a two-qubit gate fidelity of up to 99.72%. This performance is comparable to the highest values reported in the literature of superconducting circuits. Thus our work, for the first time within the realm of superconducting qubits, reveals an approach toward fault-tolerant quantum computing that is alternative and competitive to the transmon system.
arxiv pdf

Compiling Arbitrary Single-Qubit Gates Via the Phase-Shifts of Microwave Pulses

  1. Jianxin Chen,
  2. Dawei Ding,
  3. Cupjin Huang,
  4. and Qi Ye
Realizing an arbitrary single-qubit gate is a precursor for many quantum computational tasks, including the conventional approach to universal quantum computing. For superconducting
qubits, single-qubit gates are usually realized by microwave pulses along drive or flux lines. These pulses are calibrated to realize a particular single-qubit gate. However, it is clearly impractical to calibrate a pulse for every possible single-qubit gate in SU(2). On the other hand, compiling arbitrary gates using a finite universal gate set will lead to unacceptably low fidelities. Here, we provide a compilation scheme for arbitrary single-qubit gates for which the three real parameters of the gate directly correspond to the phase shifts of microwave pulses, which can be made extremely accurate experimentally, that is also compatible with any two-qubit gate. Furthermore, we only require the calibration of the Xπ and Xπ2 pulses, gates that are already necessary for tasks such as Clifford-based randomized benchmarking as well as measuring the T1 and T2 decoherence parameters.
arxiv pdf