Quantum metasurfaces as probes of vacuum particle content

The quantum vacuum of the electromagnetic field contains spatially localised particle content. We propose to probe this content in the non-perturbative regime of boundary-condition changes using a quantum mirror — a two-dimensional sub-wavelength atomic array dividing a photonic cavity. Its reflectivity is quantum-controlled by a single Rydberg atom, creating coherent superpositions of transmissive and reflective states. Unlike parametric dynamical-Casimir approaches, this platform enables boundary changes that non-perturbatively alter the cavity-mode structure, directly coupling to the particle content of the vacuum. This opens an experimental route to observing superposed Dirchtlet boundary conditions, superpositions of particle creation effects and the dynamical casimir effect with highly non-perturbative boundary condition changes.