Polarization-independent zero-directional scattering without geometric symmetries

As the characteristic feature of the generalized Kerker effect in Mie theory, directional scattering elimination has been playing a pivotal role in nanophotonics and many other photonic disciplines, such as singular optics and topological photonics. Generally, zero-directional scattering can be obtained only for a specific incident polarization, and to make it fully independent of arbitrary polarizations would require scatterers that exhibit geometric (e.g., mirror) symmetries. Here, we revisit the generalized Kerker effect and directional scattering elimination not from the perspective of conventional electromagnetic multipoles, but rather quasinormal modes supported by non-Hermitian systems. We reveal how to obtain zero-directional scattering that is independent of arbitrary incident polarizations, even for scattering structures that do not exhibit the required geometric symmetries. Such geometric symmetry-free and polarization-independent responses are made accessible through a synchronous exploitation of electromagnetic reciprocity and geometric phase. Our discovery can stimulate fundamental explorations and practical applications in not only photonics, but also many other wave physics branches where scattering and geometric phases are pervasive.