近日，香港科技大学的Gyu-Boong Jo及其研究小组与北京大学的刘雄军等人合作并取得一项新进展。经过不懈努力，他们揭示超冷费米气体中的二维非厄米趋肤效应。相关研究成果已于2025年1月8日在国际权威学术期刊《自然》上发表。

该研究团队为处于自旋-轨道耦合光晶格中的超冷费米子创建了一个具有可调耗散的二维（2D）非厄米拓扑能带，该能带展现出非厄米趋肤效应（NHSE）。研究人员首先在实验上证明了在存在非零耗散的情况下，复能量平面上存在明显的非零谱绕数，从而确立了二维趋肤效应的存在。此外，研究人员通过监测原子的质心运动，在实空间中观察到了非厄米趋肤效应的动力学特征。

最后，研究人员还证明了在动量空间中形成了一对特殊点，它们通过一条开放的体费米弧相连，这与厄米系统中发现的闭合环路形成对比。随着耗散的增加，这对异常点出现并移动，从而形成了费米弧。这项研究工作为在高维度中模拟非厄米物理的进一步研究奠定了基础，并为理解量子统计与非厄米趋肤效应的相互作用开辟了道路。

据悉，非厄米性的概念拓展了人们对能带拓扑的理解，催生出诸多反直觉的现象。非厄米趋肤效应（NHSE）便是其中一例，该效应表现为本征态在边界上的集中。然而，尽管高维非厄米量子系统在弯曲空间、高阶拓扑相和黑洞等领域可能带来深刻见解，但这一效应在高维空间中的实现尚未被探索。

附：英文原文

Title: Two-dimensional non-Hermitian skin effect in an ultracold Fermi gas

Author: Zhao, Entong, Wang, Zhiyuan, He, Chengdong, Poon, Ting Fung Jeffrey, Pak, Ka Kwan, Liu, Yu-Jun, Ren, Peng, Liu, Xiong-Jun, Jo, Gyu-Boong

Issue&Volume: 2025-01-08

Abstract: The concept of non-Hermiticity has expanded the understanding of band topology, leading to the emergence of counter-intuitive phenomena. An example is the non-Hermitian skin effect (NHSE), which involves the concentration of eigenstates at the boundary. However, despite the potential insights that can be gained from high-dimensional non-Hermitian quantum systems in areas such as curved space, high-order topological phases and black holes, the realization of this effect in high dimensions remains unexplored. Here we create a two-dimensional (2D) non-Hermitian topological band for ultracold fermions in spin–orbit-coupled optical lattices with tunable dissipation, which exhibits the NHSE. We first experimentally demonstrate pronounced nonzero spectral winding numbers in the complex energy plane with nonzero dissipation, which establishes the existence of 2D skin effect. Furthermore, we observe the real-space dynamical signature of NHSE in real space by monitoring the centre of mass motion of atoms. Finally, we also demonstrate that a pair of exceptional points are created in the momentum space, connected by an open-ended bulk Fermi arc, in contrast to closed loops found in Hermitian systems. The associated exceptional points emerge and shift with increasing dissipation, leading to the formation of the Fermi arc. Our work sets the stage for further investigation into simulating non-Hermitian physics in high dimensions and paves the way for understanding the interplay of quantum statistics with NHSE.

DOI: 10.1038/s41586-024-08347-3

Source: https://www.nature.com/articles/s41586-024-08347-3