标题： 复杂非厄米系统的散射奇点的新拓扑结构与操控 显示英文标题

标题： Novel Topology and Manipulation of Scattering Singularities in Complex non-Hermitian Systems

摘要： 在复杂的非厄米设置中控制波散射是一个令人兴奋的研究课题——常常挑战研究人员的创造力并激发公众的想象力。 成功的成果包括隐身斗篷、波前整形协议、有源超表面的发展等。 这些成就的核心在于我们能够设计物理结构的共振光谱的能力，而这一能力通常通过仔细施加几何和/或动力学对称性来实现。 相比之下，在缺乏人为施加几何对称性的复杂散射环境中，通过对边界条件进行主动控制，我们通过微波实验展示了操控散射算符光谱的能力。 这种主动控制使我们在二维（2D）参数空间中能够创建、破坏和重新定位特异点退化（EPD）。 EPD 的存在表明散射本征模式的合并，这会显著影响传输过程。 散射 EPD 在由二元电荷和整数环绕数表征的域中被划分，并且在二维参数空间中是拓扑稳定的，即使在洛伦兹互易性被破坏的情况下，它们与其他 EPD 相互作用时也遵守环绕数守恒定律；在这种情况下，拓扑域会被破坏。 这一理解的推论是提出了一个独特的输入幅度和相位无关的 50:50 同相/正交（I/Q）功率分配器。 我们的研究为在复杂的非厄米设置中完全控制散射过程迈出了重要的一步。 显示英文摘要

摘要： The control of wave scattering in complex non-Hermitian settings is an exciting subject -- often challenging the creativity of researchers and stimulating the imagination of the public. Successful outcomes include invisibility cloaks, wavefront shaping protocols, active metasurface development, and more. At their core, these achievements rely on our ability to engineer the resonant spectrum of the underlying physical structures which is conventionally accomplished by carefully imposing geometrical and/or dynamical symmetries. In contrast, by taking active control over the boundary conditions in complex scattering environments which lack artificially-imposed geometric symmetries, we demonstrate via microwave experiments the ability to manipulate the spectrum of the scattering operator. This active control empowers the creation, destruction and repositioning of exceptional point degeneracies (EPD's) in a two-dimensional (2D) parameter space. The presence of EPD's signifies a coalescence of the scattering eigenmodes, which dramatically affects transport. The scattering EPD's are partitioned in domains characterized by a binary charge, as well as an integer winding number, are topologically stable in the two-dimensional parameter space, and obey winding number-conservation laws upon interactions with each other, even in cases where Lorentz reciprocity is violated; in this case the topological domains are destroyed. Ramifications of this understanding is the proposition for a unique input-magnitude and phase-insensitive 50:50 in-phase/quadrature (I/Q) power splitter. Our study establishes an important step towards complete control of scattering processes in complex non-Hermitian settings.