Topologically Protected Valley-Dependent Quantum Photonic Circuits

• Published in: Physical review letters Vol. 126; no. 23; pp. 1 - 230503
• Main Authors: Chen, Yang, He, Xin-Tao, Cheng, Yu-Jie, Qiu, Hao-Yang, Feng, Lan-Tian, Zhang, Ming, Dai, Dao-Xin, Guo, Guang-Can, Dong, Jian-Wen, Ren, Xi-Feng
• Format: Journal Article
• Language: English
• Published: College Park American Physical Society 11-06-2021
• Subjects: Beam splitters; Circuit protection; Data processing; Domain walls; Entangled states; Information processing; Integrated optics; Interference; Photonics; Quantum phenomena; Topological insulators; Valleys; Visibility
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.126.230503

Topological photonics has been introduced as a powerful platform for integrated optics, since it can deal with robust light transport, and be further extended to the quantum world. Strikingly, valley-contrasting physics in topological photonic structures contributes to valley-related edge states, their unidirectional coupling, and even valley-dependent wave division in topological junctions. Here, we design and fabricate nanophotonic topological harpoon-shaped beam splitters (HSBSs) based on 120-deg-bending interfaces and demonstrate the first on-chip valley-dependent quantum information process. Two-photon quantum interference, namely, Hong-Ou-Mandel interference with a high visibility of 0.956±0.006, is realized with our 50/50 HSBS, which is constructed by two topologically distinct domain walls. Cascading this kind of HSBS together, we also demonstrate a simple quantum photonic circuit and generation of a path-entangled state. Our work shows that the photonic valley state can be used in quantum information processing, and it is possible to realize more complex quantum circuits with valley-dependent photonic topological insulators, which provides a novel method for on-chip quantum information processing.