Topological spin-orbit-coupled fermions beyond rotating wave approximation

Han Zhang; Wen-Wei Wang; Chang Qiao; Long Zhang; Ming-Cheng Liang; Rui Wu; Xu-Jie Wang; Xiong-Jun Liu; Xibo Zhang

doi:10.1016/j.scib.2024.01.018

Topological spin-orbit-coupled fermions beyond rotating wave approximation

Sci Bull (Beijing). 2024 Mar 30;69(6):747-755. doi: 10.1016/j.scib.2024.01.018. Epub 2024 Jan 19.

Authors

Han Zhang¹, Wen-Wei Wang¹, Chang Qiao², Long Zhang³, Ming-Cheng Liang⁴, Rui Wu¹, Xu-Jie Wang¹, Xiong-Jun Liu⁵, Xibo Zhang⁶

Affiliations

¹ International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China; Collaborative Innovation Center of Quantum Matter, Beijing 100871, China.
² International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China; Collaborative Innovation Center of Quantum Matter, Beijing 100871, China. Electronic address: qiaochang@pku.edu.cn.
³ School of Physics and Institute for Quantum Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China; Hefei National Laboratory, Hefei 230088, China.
⁴ International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China; Collaborative Innovation Center of Quantum Matter, Beijing 100871, China; Beijing Academy of Quantum Information Sciences, Beijing 100193, China.
⁵ International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China; Collaborative Innovation Center of Quantum Matter, Beijing 100871, China; Hefei National Laboratory, Hefei 230088, China; International Quantum Academy, Shenzhen 518048, China. Electronic address: xiongjunliu@pku.edu.cn.
⁶ International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China; Collaborative Innovation Center of Quantum Matter, Beijing 100871, China; Hefei National Laboratory, Hefei 230088, China; Beijing Academy of Quantum Information Sciences, Beijing 100193, China. Electronic address: xibo@pku.edu.cn.

PMID: 38331706
DOI: 10.1016/j.scib.2024.01.018

Abstract

The realization of spin-orbit-coupled ultracold gases has driven a wide range of research and is typically based on the rotating wave approximation (RWA). By neglecting the counter-rotating terms, RWA characterizes a single near-resonant spin-orbit (SO) coupling in a two-level system. Here, we propose and experimentally realize a new scheme for achieving a pair of two-dimensional (2D) SO couplings for ultracold fermions beyond RWA. This work not only realizes the first anomalous Floquet topological Fermi gas beyond RWA, but also significantly improves the lifetime of the 2D-SO-coupled Fermi gas. Based on pump-probe quench measurements, we observe a deterministic phase relation between two sets of SO couplings, which is characteristic of our beyond-RWA scheme and enables the two SO couplings to be simultaneously tuned to the optimum 2D configurations. We observe intriguing band topology by measuring two-ring band-inversion surfaces, quantitatively consistent with a Floquet topological Fermi gas in the regime of high Chern numbers. Our study can open an avenue to explore exotic SO physics and anomalous topological states based on long-lived SO-coupled ultracold fermions.

Keywords: Fermi gases; Quantum simulation; Spin–orbit coupling; Topological phases of matter; Ultracold atoms.