Nontrivial spectral properties of non-Hermitian systems can lead to intriguing effects with no counterparts in Hermitian systems. For instance, in a two-mode photonic system, by dynamically winding around an exceptional point (EP) a controlled asymmetric-symmetric mode switching can be realized. That is, the system can either end up in one of its eigenstates, regardless of the initial eigenmode, or it can switch between the two states on demand, by simply controlling the winding direction. However, for multimode systems with higher-order EPs or multiple low-order EPs, the situation can be more involved, and the ability to control asymmetric-symmetric mode switching can be impeded, due to the breakdown of adiabaticity. Here we demonstrate that this difficulty can be overcome by winding around exceptional curves by additionally crossing diabolic points. We consider a four-mode \({{{{{{{\mathcal{PT}}}}}}}}\)-symmetric bosonic system as a platform for experimental realization of such a multimode switch. Our work provides alternative routes for light manipulations in non-Hermitian photonic setups.

非 Hermitian 系统的非平凡光谱特性可以导致有趣的效果，而 Hermitian 系统中没有对应物。例如，在双模光子系统中，通过围绕异常点 (EP) 动态缠绕，可以实现受控的非对称-对称模式切换。也就是说，无论初始本征模式如何，系统都可以最终处于其本征状态之一，或者它可以根据需要在两种状态之间切换，只需控制缠绕方向即可。然而，对于具有高阶 EP 或多个低阶 EP 的多模系统，情况可能会更加复杂，并且由于绝热性的破坏，控制非对称-对称模式切换的能力可能会受到阻碍。在这里，我们证明可以通过额外穿过恶魔点绕过异常曲线来克服这个困难。我们考虑四模式\({{{{{{{\mathcal{PT}}}}}}}}\) -对称玻色子系统作为实验实现这种多模开关的平台。我们的工作为非厄米光子设置中的光操作提供了替代途径。