Direct evidence for cosmic-ray-induced correlated errors in superconducting qubit array

  1. Xue-Gang Li,
  2. Jun-Hua Wang,
  3. Yao-Yao Jiang,
  4. Guang-Ming Xue,
  5. Xiao-Xia Cai,
  6. Jun Zhou,
  7. Ming Gong,
  8. Zhao-Feng Liu,
  9. Shuang-Yu Zheng,
  10. Deng-Ke Ma,
  11. Mo Chen,
  12. Wei-Jie Sun,
  13. Shuang Yang,
  14. Fei Yan,
  15. Yi-Rong Jin,
  16. Xue-Feng Ding,
  17. and Hai-Feng Yu
Correlated errors can significantly impact the quantum error correction, which challenges the assumption that errors occur in different qubits independently in both space and time.
Superconducting qubits have been found to suffer correlated errors across multiple qubits, which could be attributable to ionizing radiations and cosmic rays. Nevertheless, the direct evidence and a quantitative understanding of this relationship are currently lacking. In this work, we propose to continuously monitor multi-qubit simultaneous charge-parity jumps to detect correlated errors and find that occur more frequently than multi-qubit simultaneous bit flips. Then, we propose to position two cosmic-ray muon detectors directly beneath the sample box in a dilution refrigerator and successfully observe the correlated errors in a superconducting qubit array triggered by muons. By introducing a lead shielding layer on the refrigerator, we also reveal that the majority of other correlated errors are primarily induced by gamma rays. Furthermore, we find the superconducting film with a higher recombination rate of quasiparticles used in the qubits is helpful in reducing the duration of correlated errors. Our results provide experimental evidence of the impact of gamma rays and muons on superconducting quantum computation and offer practical insights into mitigation strategies for quantum error correction. In addition, we observe the average occurrence rate of muon-induced correlated errors in our processor is approximately 0.40 min−1cm−2, which is comparable to the muon event rate detected by the muon detector with 0.506 min−1cm−2. This demonstrates the potential applications of superconducting qubit arrays as low-energy threshold sensors in the field of high-energy physics.

Experimental Measurement of the Quantum Metric Tensor and Related Topological Phase Transition with a Superconducting Qubit

  1. Xinsheng Tan,
  2. Dan-Wei Zhang,
  3. Zhen Yang,
  4. Ji Chu,
  5. Yan-Qing Zhu,
  6. Danyu Li,
  7. Xiaopei Yang,
  8. Shuqing Song,
  9. Zhikun Han,
  10. Zhiyuan Li,
  11. Yuqian Dong,
  12. Hai-Feng Yu,
  13. Hui Yan,
  14. Shi-Liang Zhu,
  15. and Yang Yu
Berry curvature is an imaginary component of the quantum geometric tensor (QGT) and is well studied in many branches of modern physics; however, the quantum metric as a real component
of the QGT is less explored. Here, by using tunable superconducting circuits, we experimentally demonstrate two methods to directly measure the quantum metric tensor for characterizing the geometry and topology of underlying quantum states in parameter space. The first method is to probe the transition probability after a sudden quench, and the second one is to detect the excitation rate under weak periodic driving. Furthermore, based on quantum-metric and Berry-curvature measurements, we explore a topological phase transition in a simulated time-reversal-symmetric system, which is characterized by the Euler characteristic number instead of the Chern number. The work opens up a unique approach to explore the topology of quantum states with the QGT.

Topological Maxwell Metal Bands in a Superconducting Qutrit

  1. Xinsheng Tan,
  2. Dan-Wei Zhang,
  3. Qiang Liu,
  4. Guangming Xue,
  5. Hai-Feng Yu,
  6. Yan-Qing Zhu,
  7. Hui Yan,
  8. Shi-Liang Zhu,
  9. and Yang Yu
We experimentally explore the topological Maxwell metal bands by mapping the momentum space of condensed-matter models to the tunable parameter space of superconducting quantum circuits.
An exotic band structure that is effectively described by the spin-1 Maxwell equations is imaged. Three-fold degenerate points dubbed Maxwell points are observed in the Maxwell metal bands. Moreover, we engineer and observe the topological phase transition from the topological Maxwell metal to a trivial insulator, and report the first experiment to measure the Chern numbers that are higher than one.