报告题目：Generalization of exceptional points: high-dimensional coalescing non-Hermitian spaces
报 告 人：马冠聪 教授（香港浸会大学物理系）
报告时间：2025年10月23日（周四）下午16:10
报告地点：吃瓜网站
A-201
报告摘要：
Exceptional points (EPs) are spectral singularities in non-Hermitian systems, at which individual eigenvalues and eigenvectors become identical. The successful realization of EPs in diverse physical systems, such as photonics, acoustics, cold atoms, and superconducting circuits, has triggered tremendous interest in fundamental physics and inspired a vast array of novel applications. However, as the term “exceptional” suggests, EPs are usually isolated spectral points. Consequently, functionalities rooted in EPs face several inherent limitations, such as narrow bandwidth. Here, we present a generalization of the concept of EPs characterized by the coalescence of multi-dimensional Hilbert subspaces and overlapped spectra. This condition is denoted as “exceptional deficiency” (ED). When this happens, two Hilbert subspaces of identical but arbitrarily large dimensions exactly align, accompanied by the coincidence of their spectra. Consequently, the full Hilbert space is highly defective by “missing” half of its span. In the meantime, the spectrum is entirely composed of EPs.
The condition of ED can be reached in a large variety of systems. We present its realization in a one-dimensional double-chain lattice. Intriguingly, the ED can break the bulk-edge correspondence of non-Hermitian skin effects, which relates nontrivial point-gap topology to the existence of skin modes. As a consequence, we find that the ED underpins new non-Hermitian phenomena characterized by the synergy of skin effects and propagation.
Reference
Zhen Li, Xulong Wang, Rundong Cai, Kenji Shimomura, Zhesen Yang, Masatoshi Sato, Guancong Ma, “Exceptional deficiency of non-Hermitian systems: high-dimensional coalescence and dynamics,” arXiv:2504.12238 (2025).
报告人简介：
Dr. Guancong Ma is currently a professor of physics at Hong Kong Baptist University. He received his B.Sc. in Applied Physics from the South China University of Technology in 2007, followed by a Ph.D. in Physics from the Hong Kong University of Science and Technology in 2012. After that, he became a postdoctoral fellow at the Institute for Advanced Study and the Department of Physics at the same institution until 2017, when he joined the Department of Physics at Hong Kong Baptist University. He now serves on the Executive Committee of the Physical Society of Hong Kong. Dr. Ma was awarded the “Young Investigator Award 2021” by the International Phononics Society and was selected as one of the “Top 10 Rising Stars in Science and Technology 2021” by the China Association for Science and Technology. He is the recipient of the C. N. Yang Award in 2022, awarded by the Association of Asia Pacific Physical Societies and the Asia Pacific Center for Theoretical Physics.
Dr. Ma conducts research on various topics in topological and non-Hermitian physics using classical-wave platforms, with a focus on acoustics. He is also interested in metamaterials and complex waves. He has published over 60 papers in peer-reviewed journals, including Science, Nature, Nature Research Journals, Physical Review X, Physical Review Letters, etc. His papers have received over 10,000 citations. He also holds 8 US patents, and 9 Chinese invention patents.
邀 请 人：肖孟 教授
