Kaixuan Huang

Observation of critical phase transition in a generalized Aubry-André-Harper model on a superconducting quantum processor with tunable couplers

  1. Hao Li,
  2. Yong-Yi Wang,
  3. Yun-Hao Shi,
  4. Kaixuan Huang,
  5. Xiaohui Song,
  6. Gui-Han Liang,
  7. Zheng-Yang Mei,
  8. Bozhen Zhou,
  9. He Zhang,
  10. Jia-Chi Zhang,
  11. Shu Chen,
  12. Shiping Zhao,
  13. Ye Tian,
  14. Zhan-Ying Yang,
  15. Zhongcheng Xiang,
  16. Kai Xu,
  17. Dongning Zheng,
  18. and Heng Fan
Quantum simulation enables study of many-body systems in non-equilibrium by mapping to a controllable quantum system, providing a new tool for computational intractable problems. Here,
using a programmable quantum processor with a chain of 10 superconducting qubits interacted through tunable couplers, we simulate the one-dimensional generalized Aubry-André-Harper model for three different phases, i.e., extended, localized and critical phases. The properties of phase transitions and many-body dynamics are studied in the presence of quasi-periodic modulations for both off-diagonal hopping coefficients and on-site potentials of the model controlled respectively by adjusting strength of couplings and qubit frequencies. We observe the spin transport for initial single- and multi-excitation states in different phases, and characterize phase transitions by experimentally measuring dynamics of participation entropies. Our experimental results demonstrate that the newly developed tunable coupling architecture of superconducting processor extends greatly the simulation realms for a wide variety of Hamiltonians, and may trigger further investigations on various quantum and topological phenomena.
arxiv pdf

Metrological characterisation of non-Gaussian entangled states of superconducting qubits

  1. Kai Xu,
  2. Yu-Ran Zhang,
  3. Zheng-Hang Sun,
  4. Hekang Li,
  5. Pengtao Song,
  6. Zhongcheng Xiang,
  7. Kaixuan Huang,
  8. Hao Li,
  9. Yun-Hao Shi,
  10. Chi-Tong Chen,
  11. Xiaohui Song,
  12. Dongning Zheng,
  13. Franco Nori,
  14. H. Wang,
  15. and Heng Fan
Multipartite entangled states are significant resources for both quantum information processing and quantum metrology. In particular, non-Gaussian entangled states are predicted to
achieve a higher sensitivity of precision measurements than Gaussian states. On the basis of metrological sensitivity, the conventional linear Ramsey squeezing parameter (RSP) efficiently characterises the Gaussian entangled atomic states but fails for much wider classes of highly sensitive non-Gaussian states. These complex non-Gaussian entangled states can be classified by the nonlinear squeezing parameter (NLSP), as a generalisation of the RSP with respect to nonlinear observables, and identified via the Fisher information. However, the NLSP has never been measured experimentally. Using a 19-qubit programmable superconducting processor, here we report the characterisation of multiparticle entangled states generated during its nonlinear dynamics. First, selecting 10 qubits, we measure the RSP and the NLSP by single-shot readouts of collective spin operators in several different directions. Then, by extracting the Fisher information of the time-evolved state of all 19 qubits, we observe a large metrological gain of 9.89[Math Processing Error] dB over the standard quantum limit, indicating a high level of multiparticle entanglement for quantum-enhanced phase sensitivity. Benefiting from high-fidelity full controls and addressable single-shot readouts, the superconducting processor with interconnected qubits provides an ideal platform for engineering and benchmarking non-Gaussian entangled states that are useful for quantum-enhanced metrology.
arxiv pdf