Lu Yong-Heng, Wang Yao, Mei Feng, Chang Yi-Jun, Zheng Hang, Jia Suotang, Jin Xian-Min
Center for Integrated Quantum Information Technologies (IQIT), School of Physics and Astronomy and State Key Laboratory of Advanced Optical Communication Systems and Networks, Shanghai Jiao Tong University, Shanghai 200240, China.
CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
Nanophotonics. 2021 Nov 26;11(1):153-160. doi: 10.1515/nanoph-2021-0559. eCollection 2022 Jan.
First- and second-order topological phases, capable of inherent protection against disorder of materials, have been recently experimentally demonstrated in various artificial materials through observing the topologically protected edge states. Topological phase transition represents a new class of quantum critical phenomena, which is accompanied by the changes related to the bulk topology of energy band structures instead of symmetry. However, it is still a challenge to directly observe the topological phase transitions defined in terms of bulk states. Here, we theoretically and experimentally demonstrate the direct observation of multifarious topological phase transitions with real-space indicator in a single photonic chip, which is formed by integration of 324 × 33 waveguides supporting both first- and second-order topological phases. The trivial-to-first-order, trivial-to-second-order and first-to-second-order topological phase transitions signified by the band gap closure can all be directly detected via photon evolution in the bulk. We further observe the creation and destruction of gapped topological edge states associated with these topological phase transitions. The bulk-state-based route to investigate the high-dimensional and high-order topological features, together with the platform of freely engineering topological materials by three-dimensional laser direct writing in a single photonic chip, opens up a new avenue to explore the mechanisms and applications of artificial devices.
一阶和二阶拓扑相能够对材料的无序提供内在保护，最近已通过观察拓扑保护的边缘态在各种人工材料中得到实验证明。拓扑相变代表了一类新的量子临界现象，它伴随着与能带结构的体拓扑相关的变化而非对称性。然而，直接观测由体态定义的拓扑相变仍然是一个挑战。在此，我们通过理论和实验证明了在单个光子芯片中利用实空间指标直接观测多种拓扑相变，该光子芯片由324×33个支持一阶和二阶拓扑相的波导集成而成。由带隙闭合所表征的从平凡到一阶、从平凡到二阶以及从一阶到二阶的拓扑相变都可以通过体中的光子演化直接检测到。我们还进一步观测到了与这些拓扑相变相关的带隙拓扑边缘态的产生和消失。基于体态来研究高维和高阶拓扑特征，以及通过三维激光直写在单个光子芯片中自由设计拓扑材料的平台，为探索人工器件的机制和应用开辟了一条新途径。
