Non-Hermitian spectral singularities including bound states in the continuum (BICs) and exceptional points (EPs) enable powerful forms of wave control but remain challenging to implement in planar, passive magnonic systems. Here, we realize reflection-based BICs and near-EP behavior in a fully integrated cavity–magnonic platform dominated by coherent magnon–photon coupling. Interference between a Fabry–Perot-like cavity mode and a tunable YIG magnon produces a reflection-zero state with sharply enhanced group delay, identifying a BIC. Equivalently, this BIC can be formulated in a non-Hermitian scattering-Hamiltonian framework, where it appears as a reflection zero in the S-matrix. By adjusting the coherent coupling conditions and exploiting direction-dependent loading, we steer the system toward an effective PT-symmetric operating point and observe direction-selective polaritonic coherent perfect absorption (CPA). Our results establish reflection as a robust channel for accessing non-Hermitian phenomena in hybrid magnonic devices and provide a geometry-based route to reconfigurable, compact wave-control functionalities.
Kim et al. (Fri,) studied this question.