Long-lived topological time-crystalline order on a quantum processor

  1. Liang Xiang,
  2. Wenjie Jiang,
  3. Zehang Bao,
  4. Zixuan Song,
  5. Shibo Xu,
  6. Ke Wang,
  7. Jiachen Chen,
  8. Feitong Jin,
  9. Xuhao Zhu,
  10. Zitian Zhu,
  11. Fanhao Shen,
  12. Ning Wang,
  13. Chuanyu Zhang,
  14. Yaozu Wu,
  15. Yiren Zou,
  16. Jiarun Zhong,
  17. Zhengyi Cui,
  18. Aosai Zhang,
  19. Ziqi Tan,
  20. Tingting Li,
  21. Yu Gao,
  22. Jinfeng Deng,
  23. Xu Zhang,
  24. Hang Dong,
  25. Pengfei Zhang,
  26. Si Jiang,
  27. Weikang Li,
  28. Zhide Lu,
  29. Zheng-Zhi Sun,
  30. Hekang Li,
  31. Zhen Wang,
  32. Chao Song,
  33. Qiujiang Guo,
  34. Fangli Liu,
  35. Zhe-Xuan Gong,
  36. Alexey V. Gorshkov,
  37. Norman Y. Yao,
  38. Thomas Iadecola,
  39. Francisco Machado,
  40. H. Wang,
  41. and Dong-Ling Deng
Topologically ordered phases of matter elude Landau’s symmetry-breaking theory, featuring a variety of intriguing properties such as long-range entanglement and intrinsic robustness
against local perturbations. Their extension to periodically driven systems gives rise to exotic new phenomena that are forbidden in thermal equilibrium. Here, we report the observation of signatures of such a phenomenon — a prethermal topologically ordered time crystal — with programmable superconducting qubits arranged on a square lattice. By periodically driving the superconducting qubits with a surface-code Hamiltonian, we observe discrete time-translation symmetry breaking dynamics that is only manifested in the subharmonic temporal response of nonlocal logical operators. We further connect the observed dynamics to the underlying topological order by measuring a nonzero topological entanglement entropy and studying its subsequent dynamics. Our results demonstrate the potential to explore exotic topologically ordered nonequilibrium phases of matter with noisy intermediate-scale quantum processors.

Observation of a symmetry-protected topological time crystal with superconducting qubits

  1. Xu Zhang,
  2. Wenjie Jiang,
  3. Jinfeng Deng,
  4. Ke Wang,
  5. Jiachen Chen,
  6. Pengfei Zhang,
  7. Wenhui Ren,
  8. Hang Dong,
  9. Shibo Xu,
  10. Yu Gao,
  11. Feitong Jin,
  12. Xuhao Zhu,
  13. Qiujiang Guo,
  14. Hekang Li,
  15. Chao Song,
  16. Zhen Wang,
  17. Dong-Ling Deng,
  18. and H. Wang
We report the observation of a symmetry-protected topological time crystal, which is implemented with an array of programmable superconducting qubits. Unlike the time crystals reported
in previous experiments, where spontaneous breaking of the discrete time translational symmetry occurs for local observables throughout the whole system, the topological time crystal observed in our experiment breaks the time translational symmetry only at the boundaries and has trivial dynamics in the bulk. More concretely, we observe robust long-lived temporal correlations and sub-harmonic temporal response for the edge spins up to 40 driving cycles. We demonstrate that the sub-harmonic response is independent of whether the initial states are random product states or symmetry-protected topological states, and experimentally map out the phase boundary between the time crystalline and thermal phases. Our work paves the way to exploring peculiar non-equilibrium phases of matter emerged from the interplay between topology and localization as well as periodic driving, with current noisy intermediate-scale quantum processors.

Generation and controllable switching of superradiant and subradiant states in a 10-qubit superconducting circuit

  1. Zhen Wang,
  2. Hekang Li,
  3. Wei Feng,
  4. Xiaohui Song,
  5. Chao Song,
  6. Wuxin Liu,
  7. Qiujiang Guo,
  8. Xu Zhang,
  9. Hang Dong,
  10. Dongning Zheng,
  11. H. Wang,
  12. and Da-Wei Wang
Superradiance and subradiance concerning enhanced and inhibited collective radiation of an ensemble of atoms have been a central topic in quantum optics. However, precise generation
and control of these states remain challenging. Here we deterministically generate up to 10-qubit superradiant and 8-qubit subradiant states, each containing a single excitation, in a superconducting quantum circuit with multiple qubits interconnected by a cavity resonator. The N−−√-scaling enhancement of the coupling strength between the superradiant states and the cavity is validated. By applying appropriate phase gate on each qubit, we are able to switch the single collective excitation between superradiant and subradiant states. While the subradiant states containing a single excitation are forbidden from emitting photons, we demonstrate that they can still absorb photons from the resonator. However, for even number of qubits, a singlet state with half of the qubits being excited can neither emit nor absorb photons, which is verified with 4 qubits. This study is a step forward in coherent control of collective radiation and has promising applications in quantum information processing.

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.