Metamaterials constructed from deep subwavelength building blocks have been used to demonstrate phenomena ranging from negative refractive index and ε-near-zero to cloaking, emulations of general relativity, and superresolution imaging. More recently, metamaterials have been suggested as a new platform for quantum optics. We present the use of a dielectric metasurface to generate entanglement between the spin and orbital angular momentum of photons. We demonstrate the generation of the four Bell states on a single photon by using the geometric phase that arises from the photonic spin-orbit interaction and subsequently show nonlocal correlations between two photons that interacted with the metasurface. Our results show that metamaterials are suitable for the generation and manipulation of entangled photon states, introducing the area of quantum optics metamaterials.

Disordered structures give rise to intriguing phenomena owing to the complex nature of their interaction with light. We report on photonic spin-symmetry breaking and unexpected spin-optical transport phenomena arising from subwavelength-scale disordered geometric phase structure. Weak disorder induces a photonic spin Hall effect, observed via quantum weak measurements, whereas strong disorder leads to spin-split modes in momentum space, a random optical Rashba effect. Study of the momentum space entropy reveals an optical transition upon reaching a critical point where the structure's anisotropy axis vanishes. Incorporation of singular topology into the disordered structure demonstrates repulsive vortex interaction depending on the disorder strength. The photonic disordered geometric phase can serve as a platform for the study of different phenomena emerging from complex media involving spin-orbit coupling.

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Metasurfaces enable the manipulation of light’s disorder strength in a two-dimensional photonic system. Here we report on the spectral interleaving of an ordered and a disordered system within a geometric phase metasurface. The efficiency of prevalent interleaving techniques is limited by the number of functions incorporated within the metasurface. We present a shared-aperture extinction cross-section approach relying on interleaving of spectrally selective nanoantenna arrays, each having a large extinction cross-section, thus allowing to overcome this limitation. Using this approach, we realize a silicon-based spectral interleaving metasurface for spectrum-dependent disguise, holographic tagging, and imaging of a target object. The shared-aperture extinction cross-section concept opens the path for the generation of multiple, efficient, and spectrally resolved functions in a two-dimensional photonic system. The presented order–disorder interleaving approach offers new prospects for the manipulation of light’s entropy.

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