报告题目：Exploring exotic topological quantum matter

报告专家：汪子丹 教授

报告时间：3月6日(周三) 10:00-11:30

报告地点：主校区物理学院C楼319

报告摘要：

Symmetry plays a key role in exploring many topological phases. In this talk, (1) I will address non-Hermitian spatial symmetries, a class of symmetries that have no counterparts in Hermitian systems, and how normal and exceptional topological semimetals can be stabilized by these symmetries. Notably, the nonlocal Hermitian conjugate pair of exceptional or normal band degeneracies may be enforced by non-Hermitian spatial symmetries. Remarkably, it is found that these pairs lead to the symmetry-enforced violation of the Fermion doubling theorem in the long-time limit. On the other hand, for time-reversal and sublattice symmetries, there are six ramified symmetry classes leading to novel topological classifications with various non-Hermitian skin effects. As artificial crystals are the main experimental platforms for non-Hermitian physics, there exists the symmetry barrier for realizing topological physics in the six ramified symmetry classes. Here we present a general mechanism to cross the symmetry barrier, suggesting that gauge structures may significantly enrich non-Hermitian physics at the fundamental level. (2) I will elaborate an arresting theoretical scenario for emulating the famous magneto-optical (MO) Faraday effect using ultracold atomic gases, in which an artificial MO Faraday effect is readily signaled by the spin imbalance of atoms, with the setup of laser fields offering a high controllability for quantum manipulation. In addition, with the underlying polarization state being extracted in the synthetic dimension, the artificial MO effect can emerge under an entirely different mechanism from the conventional picture, and the MO rotation is particularly related to the bulk topology in synthetic dimensions, providing an unambiguous evidence for the desired topological MO effect.

专家简介：

汪子丹，香港大学物理系讲座教授，兼香港量子研究院院长。曾获国家自然科学奖二等奖等多项国家和省部级科技奖励，并入选教育部长江学者讲座教授、国家基金委海外杰青等人才项目。长期从事量子物理和凝聚态物理的理论研究，在量子几何相位、量子计算、拓扑物理等前沿领域做出了一系列创新性研究成果。