Abstract
Manipulating topological invariants is possible by modifying the global properties of optical devices to alter their band structures. This could be achieved by statically altering devices or dynamically reconfiguring devices with considerably different geometric parameters, even though it inhibits switching speed. Recently, optical nonlinearity has emerged as a tool for tailoring topological and non-Hermitian (NH) properties, promising fast manipulation of topological phases. In this work, we observe topologically protected NH phase transitions driven by optical nonlinearity in a silicon nanophotonic Floquet topological insulator. The phase transition occurs from forbidden bandgaps to NH conducting edge modes, which emerge at a nonlinearity-induced gain–loss junction along the boundaries of a topological insulator. We find static NH edge modes and dynamic phase transitions involving exceptional points at a speed of hundreds of picoseconds, which inherently retain topological protections against fabrication imperfections. This work shows an interplay between topology and non-Hermiticity by means of nonlinear optics, and it provides a way of manipulating multiple phase transitions at high speeds that is applicable to many other materials with strong nonlinearities, which could promote the development of unconventionally robust light-controlled devices for classical and quantum applications.
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Data availability
The data that support the findings of this study are available from the corresponding authors upon reasonable request. Source data are provided with this paper.
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Acknowledgements
We acknowledge support from the National Natural Science Foundation of China (grant nos. 12325410, 61975001, 61590933, 11734001, 91950204, 92150302, 11527901,61904196, 62274179 and 62235001), the Innovation Program for Quantum Science and Technology (grant no. 2021ZD0301500), the National Key R&D Program of China (grant nos. 2019YFA0308702, 2018YFA0704404 and 2022YFB2802400), Beijing Natural Science Foundation (grant nos. Z190005 and Z220008), the Guangdong Major Project of Basic and Applied Basic Research (grant no. 2020B0301030009) and the Key R&D Program of Guangdong Province (grant no. 2018B030329001).
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T.D. and J.W. conceived the project. T.D., J.M., Y.Y., Y.Z., C.Z. and B.T. implemented the experiment. T.D. provided the simulations and performed the theoretical analysis. T.D., Y.A., Y.L. and J.Y. discussed and improved the theoretical results. Z.L., J.L., W.W., X.H., Q.G. and J.W. managed the project. T.D. and J.W. wrote the manuscript with input from all the authors. All the authors discussed the results and contributed to the manuscript.
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Nature Physics thanks Jiangbin Gong and the other anonymous reviewer(s) for their contribution to the peer review of this work.
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Dai, T., Ao, Y., Mao, J. et al. Non-Hermitian topological phase transitions controlled by nonlinearity. Nat. Phys. 20, 101–108 (2024). https://doi.org/10.1038/s41567-023-02244-8
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DOI: https://doi.org/10.1038/s41567-023-02244-8
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