Wang Yunhan, Wu Yang, Ye Xiangyu, Duan Chang-Kui, Wang Ya, Hu Haiping, Rong Xing, Du Jiangfeng
CAS Key Laboratory of Microscale Magnetic Resonance and School of Physical Sciences, University of Science and Technology of China, Hefei, China.
Hefei National Laboratory, University of Science and Technology of China, Hefei, China.
Nat Nanotechnol. 2025 Jun 6. doi: 10.1038/s41565-025-01913-4.
Non-Abelian topological transitions are well studied in Hermitian systems, exhibiting features like non-Abelian charges and edge states. Introducing non-Hermiticity gives rise to novel topological phenomena, yet non-Hermitian non-Abelian topological transitions remain experimentally unexplored. In this work we observe a non-Hermitian non-Abelian topological transition in a single electron spin system of a nitrogen vacancy centre in diamond, achieved via a dilation method with a nearby nuclear spin. While this transition cannot be detected by traditional topological numbers, we identify the transition through the measured complex eigenvalue braids. We extract the braid invariants from the relative phases between eigenvalues and thereby establish their changes as clear signatures of non-Abelian transitions. Furthermore we experimentally reveal an intriguing consequence of this transition: the creation of a third-order exceptional point through the collision of two second-order exceptional points with opposite charges. Our work unveils the dynamical interplay between exceptional points and provides guidance on the manipulation of spectral topology to achieve functionalities such as robust quantum control.
非阿贝尔拓扑相变在厄米系统中已得到充分研究，展现出诸如非阿贝尔电荷和边缘态等特征。引入非厄米性会引发新的拓扑现象，但非厄米非阿贝尔拓扑相变在实验上仍未得到探索。在这项工作中，我们在金刚石中氮空位中心的单电子自旋系统中观测到了非厄米非阿贝尔拓扑相变，这是通过对附近核自旋采用伸缩方法实现的。虽然这种相变无法通过传统拓扑数检测到，但我们通过测量复本征值辫子来识别该相变。我们从本征值之间的相对相位中提取辫子不变量，从而将它们的变化确定为非阿贝尔相变的清晰特征。此外，我们通过实验揭示了这种相变的一个有趣结果：通过两个带相反电荷的二阶例外点的碰撞产生了一个三阶例外点。我们的工作揭示了例外点之间的动态相互作用，并为操纵光谱拓扑以实现诸如稳健量子控制等功能提供了指导。
