Li Meng, Li Chu, Yan Linyu, Li Qiang, Gong Qihuang, Li Yan
State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing, 100871, China.
Frontiers Science Center for Nano-Optoelectronics, Peking University, Beijing, 100871, China.
Light Sci Appl. 2023 Nov 2;12(1):262. doi: 10.1038/s41377-023-01307-y.
Anomalous Floquet topological insulators with vanishing Chern numbers but supporting chiral edge modes are attracting more and more attention. Since the existing anomalous Floquet topological insulators usually support only one kind of chiral edge mode even at a large lattice size, they are unscalable and unapplicable for multistate topological quantum systems. Recently, fractal topological insulators with self-similarity have been explored to support more nontrivial modes. Here, we demonstrate the first experimental realization of fractal photonic anomalous Floquet topological insulators based on dual Sierpinski carpet consisting of directional couplers using the femtosecond laser direct writing. The fabricated lattices support much more kinds of chiral edge states with fewer waveguides and enable perfect hopping of quantum states with near unit transfer efficiency. Instead of zero-dimensional bound modes for quantum state transport in previous laser direct-written topological insulators, we generate multiple propagating single-photon chiral edge states in the fractal lattice and observe high-visibility quantum interferences. These suggest the successful realization of highly indistinguishable single-photon chiral edge states, which can be applied in various quantum operations. This work provides the potential for enhancing the multi-fold manipulation of quantum states, enlarging the encodable quantum information capacity in a single lattice via high-dimensional encoding and many other fractal applications.
具有零陈数但支持手性边缘模式的反常弗洛凯拓扑绝缘体正吸引着越来越多的关注。由于现有的反常弗洛凯拓扑绝缘体即使在大晶格尺寸下通常也只支持一种手性边缘模式，它们不可扩展且不适用于多态拓扑量子系统。最近，具有自相似性的分形拓扑绝缘体已被探索以支持更多非平凡模式。在此，我们展示了基于由定向耦合器组成的双谢尔宾斯基地毯的分形光子反常弗洛凯拓扑绝缘体的首次实验实现，采用飞秒激光直写技术。所制备的晶格用更少的波导支持更多种类的手性边缘态，并能以接近单位传输效率实现量子态的完美跳跃。与之前激光直写拓扑绝缘体中用于量子态传输的零维束缚模式不同，我们在分形晶格中产生多个传播的单光子手性边缘态，并观察到高可见度的量子干涉。这些表明成功实现了高度不可区分的单光子手性边缘态，可应用于各种量子操作。这项工作为增强量子态的多重操控、通过高维编码在单个晶格中扩大可编码量子信息容量以及许多其他分形应用提供了潜力。
