标题： 在硅光子学中观察Floquet非厄米皮肤效应的拓扑转变 显示英文标题

标题： Observation of topology transition in Floquet non-Hermitian skin effects in silicon photonics

摘要： 非厄米物理大大丰富了我们对非平衡现象的理解，并揭示了诸如非厄米皮肤效应（NHSE）等新奇效应，该效应彻底革新了这一领域。 NHSE通常在具有非互易耦合的系统中被预测，然而这些在实验中难以实现。 没有非互易耦合的情况下，当存在共存的规范场和损耗或增益时（例如在弗洛凯非厄米系统中），NHSE也可以出现。 然而，这种弗洛凯NHSE在实验中仍大多未被探索。 在这里，我们在集成在硅光子学平台上的周期调制光学波导中实现了弗洛凯NHSE。 通过设计由周期调制引起的人工规范场，我们观察到各种弗洛凯NHSE并揭示了它们丰富的拓扑转变。 值得注意的是，我们发现了正常单极NHSE与一种非常规双极NHSE之间的转变，这种转变伴随着NHSE的方向反转。 通过复数准能量空间中的能带缠绕揭示了其背后的物理机制，该机制经历了从相同缠绕的孤立环到相反缠绕的链接环的拓扑变化。 我们的工作揭示了一条源于规范场与耗散效应相互作用的弗洛凯NHSE的新途径，并为操控光和其他波提供了根本新的方法。 显示英文摘要

摘要： Non-Hermitian physics has greatly enriched our understanding of nonequilibrium phenomena and uncovered novel effects such as the non-Hermitian skin effect (NHSE) that has profoundly revolutionized the field. NHSE is typically predicted in systems with nonreciprocal couplings which, however, are difficult to realize in experiments. Without nonreciprocal couplings, the NHSE can also emerge in systems with coexisting gauge fields and loss or gain (e.g., in Floquet non-Hermitian systems). However, such Floquet NHSE remains largely unexplored in experiments. Here, we realize the Floquet NHSEs in periodically modulated optical waveguides integrated on a silicon photonics platform. By engineering the artificial gauge fields induced by the periodical modulation, we observe various Floquet NHSEs and unveil their rich topological transitions. Remarkably, we discover the transitions between the normal unipolar NHSEs and an unconventional bipolar NHSE which is accompanied by the directional reversal of the NHSEs. The underlying physics is revealed by the band winding in complex quasienergy space which undergoes a topology change from isolated loops with the same winding to linked loops with opposite windings. Our work unfolds a new route toward Floquet NHSEs originating from the interplay between gauge fields and dissipation effects and offers fundamentally new ways for steering light and other waves.