Hui Yan

Experimental Observation of Tensor Monopoles with a Superconducting Qudit

  1. Xinsheng Tan,
  2. Dan-Wei Zhang,
  3. Danyu Li,
  4. Xiaopei Yang,
  5. Shuqing Song,
  6. Zhikun Han,
  7. Yuqian Dong,
  8. Dong Lan,
  9. Hui Yan,
  10. Shi-Liang Zhu,
  11. and Yang Yu
Monopoles play a center role in gauge theories and topological matter. Examples of monopoles include the Dirac monopole in 3D and Yang monopole in 5D, which have been extensively studied
and observed in condensed matter or artificial systems. However, tensor monopoles in 4D are less studied, and their observation has not been reported. Here we experimentally construct a tunable spin-1 Hamiltonian to generate a tensor monopole and then measure its unique features with superconducting quantum circuits. The energy structure of a 4D Weyl-like Hamiltonian with three-fold degenerate points acting as tensor monopoles is imaged. Through quantum-metric measurements, we report the first experiment that measures the Dixmier-Douady invariant, the topological charge of the tensor monopole. Moreover, we observe topological phase transitions characterized by the topological Dixmier-Douady invariant, rather than the Chern numbers as used for conventional monopoles in odd-dimensional spaces.
arxiv pdf

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.
arxiv pdf

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.
arxiv pdf