Non-Hermitian mini-workshop

6 Oct 2026, 10:00 → 7 Oct 2026, 19:00 Asia/Taipei

物理館/3-011 (PRPC 物推中心)

Discussing non-Hermitian quantum physics 

Tuesday 6 October

10:30 → 11:00 TBA, Iao-Fai Io

11:15 → 11:45 Some results on non-Hermitian lattice models and non-unitary CFTs, Heng-Hsi Li, NTU

In this talk, I am going to talk about two topics. First, I will introduce how a single PT-symmetric non-Hermitian impurity can induce exceptional points (EP) on critical Hermitian SSH models. From this, we relate the existence of EP to several physical observables that serve as evidence that the underlying structure is governed by certain non-unitary CFT. In addition, some boundary effects will be noted. On the second topic, sharing the similar structure, I will introduce three interface CFT setups motivated by hep-th setup, and discuss our recent results on the related topic. In both topics, I will try to set up the field theory description, but both of which are still work in progress.

13:20 → 14:20 Non-Hermitian Topology in Hermitian Topological Matter, Prof. Kohei Kawabata, ISSP/UTokyo

Title: Non-Hermitian Topology in Hermitian Topological Matter

Abstract:

Non-Hermiticity gives rise to distinctive topological phenomena absent in Hermitian systems. However, connection between such intrinsic non-Hermitian topology and Hermitian topology has remained largely elusive. Here, considering the bulk and boundary as an environment and system, we demonstrate that anomalous boundary states in Hermitian topological insulators exhibit non-Hermitian topology [1, 2]. We study the self-energy capturing the particle exchange between the bulk and boundary, and show that it detects Hermitian topology in the bulk and induces non-Hermitian topology at the boundary. As an illustrative example, we reveal the non-Hermitian topology and concomitant skin effect inherently embedded within chiral edge states of Chern insulators. We also identify the emergence of hinge states within effective non-Hermitian Hamiltonians at surfaces of three-dimensional topological insulators. Furthermore, we comprehensively classify our correspondence across all the tenfold symmetry classes of topological insulators and superconductors.

Based on this correspondence and K-theory, we complete the tenfold classification of Wannier localizability and detachable topological boundary states [3, 4]. While topology can impose obstructions to exponentially localized Wannier functions, certain topological insulators are exempt from such Wannier obstructions. The absence of the Wannier obstructions can further accompany topological boundary states that are detachable from the bulk bands. Here, we elucidate a close connection between these detachable topological boundary states and non-Hermitian topology. Identifying topological boundary states as non-Hermitian topology, we demonstrate that intrinsic non-Hermitian topology leads to the inevitable spectral flow. By contrast, we show that extrinsic non-Hermitian topology underlies the detachment of topological boundary states and clarify anti-Hermitian topology of the detached boundary states.

References
[1] F. Schindler, K. Gu, B. Lian, and K. Kawabata, PRX Quantum 4, 030315 (2023).
[2] S. Hamanaka, T. Yoshida, and K. Kawabata, Phys. Rev. Lett. 133, 266604 (2024).
[3] D. Nakamura, K. Shiozaki, K. Shimomura, M. Sato, and K. Kawabata, Phys. Rev. Lett. 135, 096601 (2025).
[4] K. Shiozaki, D. Nakamura, K. Shimomura, M. Sato, and K. Kawabata, Phys. Rev. B 112, 075152 (2025).

14:45 → 15:45 TBA, Prof. Chia-Yi Ju, NSYSU

Wednesday 7 October

10:30 → 11:30 TBA, Yu-Chin Tzeng, NYCU

13:30 → 14:30 Chimdessa Gashu Feyisa

14:45 → 15:45 An algebraic fractionalization of a qubit, Po-Yao Chang