复杂结构中通过局域对称性诱导的连续谱束缚态
Bound states in the continuum induced via local symmetries in complex structures
AI总结：
本文提出并实验验证了一种利用局域对称性在复杂光子网络中实现连续谱束缚态的新机制，揭示了其源于散射矩阵零点和极点的拓扑湮灭，为高Q值应用提供了新途径。
摘要：
连续谱束缚态（BICs）打破了传统认知，即认为携带能量向外传播的行波与对应离散频率的空间局域波之间存在谱分离。它们可以被描述为具有无限寿命的共振态，即零泄漏的泄漏模式。超材料和纳米光子学的出现使得在多种系统中实现BICs成为可能。目前，BICs主要通过出射共振模式之间的相消干涉实现，或利用设计的全局对称性强制使对称性不相容的束缚模式与周围辐射模式解耦。在此，我们从理论上引入了一种依赖不同机制的BICs，即局域对称性，它在不隐含任何全局对称性的情况下，将场集中约束在复杂系统的一部分上。我们利用微波在一个紧凑的一维光子网络中实验实现了此类BICs，并证明它们产生于所测散射矩阵的两个拓扑奇点——一个零点和一个极点——的湮灭。我们这种在复杂波系统中实现BICs的替代方法可能对需要高Q值模式的应用（如传感、激光以及非线性相互作用的增强）具有实用价值。
英文摘要：
Bound states in the continuum (BICs) defy conventional wisdom that assumes a spectral separation between propagating waves, that carry energy away, and spatially localized waves corresponding to discrete frequencies. They can be described as resonance states with infinite lifetime, i.e., leaky modes with zero leakage. The advent of metamaterials and nanophotonics allowed the creation of BICs in a variety of systems. Mainly, BICs have been realized by destructive interference between outgoing resonant modes or exploiting engineered global symmetries that enforce the decoupling of a symmetry-incompatible bound mode from the surrounding radiation modes. Here, we introduce theoretically BICs relying on a different mechanism, namely local symmetries that enforce a field concentration on a part of a complex system without implying any global symmetry. We experimentally implement such BICs using microwaves in a compact one-dimensional photonic network and show that they emerge from the annihilation of two topological singularities, a zero and a pole, of the measured scattering matrix. Our alternative for achieving BICs in complex wave systems may be useful for applications like sensing, lasing, and enhancement of nonlinear interactions that require high-$Q$ modes.
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