○ Speaker: Prof. Kyo-boong Cho (Dept. of Physics, Hong Kong Science & Technology Parks)
○ Title: Exploring topological matter in an atomic quantum simulator
○ Abstract: An atomic quantum simulator with ultracold atoms enables us to precisely design, characterize and understand various quantum materials on demand. In this talk, I will introduce the recent progress on the experimental realization of topological matter using ultracold atoms, and discuss a few pedagogical topological models. In particular, I will demonstrate two sets of experiments recently performed at HKUST. First, I will describe the observation of symmetry-protected topological (SPT) phases realized in 1D optical lattices . The observed SPT phase is beyond the Altland-Zirnbauer ten-fold classification, and protected by mirror and a generalized chiral symmetry that can be manipulated in an optical lattice with Raman-induced spin-orbit coupling, with its topology being detected by the spin polarization of Bloch states at highly symmetric points of the Brillouin zone. Secondly, I will discuss the realization of 3D topological band by generalizing the spin-orbit coupling realized in 1D . Despite the significant progresses, the observation of topological band beyond 2D has remained challenging due to the experimental complexity. We developed a novel way to probe 3D band structure in the presence of emergent magnetic group symmetry. This symmetry allows for effectively reconstructing the 3D topological band from a series of measurements of integrated spin textures. As a result, we demonstrate that 3D topological band structure with gapless nodal-lines are realized in simple optical lattice potentials with spin-orbit coupling. Interestingly, the spin dynamics after the quantum quench from the trivial to topological band reflects the intrinsic band topology of the post-quench Hamiltonian, which will be discussed in details for both 1D  and 3D  topological bands.
 Bo Song, Long Zhang, Chengdong He, Ting Fung Jeffrey Poon, Elnur Hajiyev, Shanchao Zhang, Xiong-Jun Liu and Gyu-Boong Jo “Observation of symmetry-protected topological band with ultracold fermions” Science Advances 4, eaao4748 (2018)  Bo Song, Chengdong He, Sen Niu, Long Zhang, Zejian Ren, Xiong-Jun Liu and Gyu-Boong Jo “Observation of nodal-line semimetal with ultracold fermions in an optical lattice” Nature Physics, in press (2019).