标题： 复杂非厄米系统中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： 在复杂非厄米环境中对波散射的控制是一个令人兴奋的课题——常常挑战研究人员的创造力，并激发公众的想象力。 成功的成果包括隐形斗篷、波前整形协议、主动超表面的发展等。 这些成就的核心依赖于我们对底层物理结构的共振谱进行工程设计的能力，这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，通过在缺乏人工施加的几何对称性的复杂散射环境中对边界条件进行主动控制，我们通过微波实验展示了操纵散射算子谱的能力。 这种主动控制使得在二维（2D）参数空间中能够创建、破坏和重新定位异常点简并（EPD's）。 EPD的存在表明散射本征模的合并，这会显著影响传输。 散射EPD被划分成由二进制电荷以及整数绕数表征的区域，在二维参数空间中具有拓扑稳定性，并且在彼此相互作用时遵守绕数守恒定律，即使在洛伦兹互易性被违反的情况下也是如此；在这种情况下，拓扑区域会被破坏。 这一理解的后果是提出了一种独特的输入幅度/相位不敏感的50:50同相/正交（I/Q）功率分配器。 我们的研究为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/phase-insensitive 50:50 in-phase/quadrature (I/Q) power splitter. Our study establishes an important step towards complete control of scattering processes.