Observation of Vectorial Phase Singularities at Zero-Eigenvalue Exceptional Points.

Exceptional points in non-Hermitian photonics provide singular responses for topological light-field control. Yet, converting such singular responses into coupled control over multiple optical degrees of freedom remains a central challenge. Here, based on a plasmonic non-Hermitian metasurface described by a reflection Jones matrix, we theoretically and experimentally reveal the parameter-space topology associated with zero-eigenvalue exceptional points. In this regime, zero-eigenvalue degeneracy preserves the singular topological features of non-Hermitian systems while elevating controllability from scalar phase modulation to coupled control of both phase and polarization, manifested as vectorial phase singularities. As a proof of concept, we implemented precise local structural tuning in a plasmonic non-Hermitian metasurface to achieve simultaneous alignment of reflection-coefficient zeros across multiple polarization channels and observed the radial collapse of scaled eigenstates on the Bloch sphere. Based on such vectorial phase singularities, we experimentally synthesized polarization-phase composite vortices, opening new avenues for high-dimensional light-field manipulation, vector holography, and topological photonic device design.