Microcavities and nanoresonators have the ability to strongly enhance many light–matter-interaction processes used in various applications in nano-optics. This enhancement is due to the resonant excitation of an electromagnetic mode that confines light in space (mode volume) and in time (quality factor). The confinement is not perfect and the modes, even dark ones, always leak some energy and have a finite lifetime. Their non-Hermitian character does significantly more than merely broadening the resonances. In this Perspective, we clarify the main difference between bound modes of Hermitian systems and leaky modes of non-Hermitian resonators, emphasizing the key existence of a spatially dependent phase factor as a signature of nonhermiticity. For decades, the phase factor has often be considered as puzzling or has even be ignored, although it plays a key role in the interpretation of many experiments on nanoscale resonant-mediated light–matter interaction, such as sensing with cavity perturbation, modification of the spontaneous emission rate, optomechanics, strong coupling, and so on. The situation has changed recently, to a point that nowadays a sound non-Hermitian formalism has been developed and freeware packages exist, helping analyze experiments that continuously push back the extraordinary limit offered by large fields for exploring matter with light.

中文翻译：

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纳米级光限制：Q 和 V

微腔和纳米谐振器能够极大地增强纳米光学中各种应用中使用的许多光-物质相互作用过程。这种增强是由于电磁模式的共振激发将光限制在空间（模式体积）和时间（品质因数）中。限制并不完美，模式，即使是暗模式，总是会泄漏一些能量并且具有有限的寿命。它们的非厄米特性不仅仅扩大了共振。在这个视角中，我们阐明了厄米系统的束缚模式和非厄米谐振器的泄漏模式之间的主要区别，强调空间相关相位因子的关键存在作为非厄密性的特征。几十年来，相位因子经常被认为是令人费解的，甚至被忽视，尽管它在解释纳米级共振介导的光-物质相互作用的许多实验中起着关键作用，例如腔扰动的传感、自发发射率的修改、光力学、强耦合等。最近情况发生了变化，现在已经开发出一种健全的非厄米形式主义，并且存在免费软件包，有助于分析实验，这些实验不断推倒大领域提供的用光探索物质的非凡极限。