Yuran Zhang

Observation of multi-component atomic Schrödinger cat states of up to 20 qubits

  1. Chao Song,
  2. Kai Xu,
  3. Hekang Li,
  4. Yuran Zhang,
  5. Xu Zhang,
  6. Wuxin Liu,
  7. Qiujiang Guo,
  8. Zhen Wang,
  9. Wenhui Ren,
  10. Jie Hao,
  11. Hui Feng,
  12. Heng Fan,
  13. Dongning Zheng,
  14. Dawei Wang,
  15. H. Wang,
  16. and Shiyao Zhu
We report on deterministic generation of 18-qubit genuinely entangled Greenberger-Horne-Zeilinger (GHZ) state and multi-component atomic Schrödinger cat states of up to 20 qubits on
a quantum processor, which features 20 superconducting qubits interconnected by a bus resonator. By engineering a one-axis twisting Hamiltonian enabled by the resonator-mediated interactions, the system of qubits initialized coherently evolves to an over-squeezed, non-Gaussian regime, where atomic Schrödinger cat states, i.e., superpositions of atomic coherent states including GHZ state, appear at specific time intervals in excellent agreement with theory. With high controllability, we are able to take snapshots of the dynamics by plotting quasidistribution Q-functions of the 20-qubit atomic cat states, and globally characterize the 18-qubit GHZ state which yields a fidelity of 0.525±0.005 confirming genuine eighteen-partite entanglement. Our results demonstrate the largest entanglement controllably created so far in solid state architectures, and the process of generating and detecting multipartite entanglement may promise applications in practical quantum metrology, quantum information processing and quantum computation.
arxiv pdf

Emulating many-body localization with a superconducting quantum processor

  1. Kai Xu,
  2. Jin-Jun Chen,
  3. Yu Zeng,
  4. Yuran Zhang,
  5. Chao Song,
  6. Wuxin Liu,
  7. Qiujiang Guo,
  8. Pengfei Zhang,
  9. Da Xu,
  10. Hui Deng,
  11. Keqiang Huang,
  12. H. Wang,
  13. Xiaobo Zhu,
  14. Dongning Zheng,
  15. and Heng Fan
The law of statistical physics dictates that generic closed quantum many-body systems initialized in nonequilibrium will thermalize under their own dynamics. However, the emergence
of many-body localization (MBL) owing to the interplay between interaction and disorder, which is in stark contrast to Anderson localization that only addresses noninteracting particles in the presence of disorder, greatly challenges this concept because it prevents the systems from evolving to the ergodic thermalized state. One critical evidence of MBL is the long-time logarithmic growth of entanglement entropy, and a direct observation of it is still elusive due to the experimental challenges in multiqubit single-shot measurement and quantum state tomography. Here we present an experiment of fully emulating the MBL dynamics with a 10-qubit superconducting quantum processor, which represents a spin-1/2 XY model featuring programmable disorder and long-range spin-spin interactions. We provide essential signatures of MBL, such as the imbalance due to the initial nonequilibrium, the violation of eigenstate thermalization hypothesis, and, more importantly, the direct evidence of the long-time logarithmic growth of entanglement entropy. Our results lay solid foundations for precisely simulating the intriguing physics of quantum many-body systems on the platform of large-scale multiqubit superconducting quantum processors.
arxiv pdf