Observation of Topologically Protected Edge States in a Photonic Two-Dimensional Quantum Walk
Phys Rev Lett. 121(10):100502 Sep 2018 

Chen, Chao; Ding, Xing; Qin, Jian; He, Yu; Luo, Yi-Han; Chen, Ming-Cheng; Liu, Chang; Wang, Xi-Lin; Zhang, Wei-Jun; Li, Hao; You, Li-Xing; Wang, Zhen; Wang, Da-Wei; Sanders, Barry C.; Lu, Chao-Yang; Pan, Jian-Wei


Periodically driven systems have displayed a variety of fascinating phenomena without analogies in static systems, which enrich the classification of quantum phases of matter and stimulate a wide range of research interests. Here, we employ discrete-time quantum walks to investigate a nontrivial topological effect unique to a two-dimensional periodically driven system: chiral edge states can exist at the interface of Floquet insulators whose Chern numbers vanish. Thanks to a resource-saving and flexible fiber-loop architecture, we realize inhomogeneous two-dimensional quantum walks up to 25 steps, over an effective 51×51 lattice with tunable local parameters. Spin-polarized chiral edge states are observed at the boundary of two distinct quantum walk domains. Our results contribute to establishing a well-controlled platform for exploring nontrivial topological phases.


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