Quantum Optics Goes Meta

Two different research groups have applied the unique properties of ultrathin dielectric metasurfaces to some problems in quantum information and communications in a pair of recent papers.

In one demonstration, researchers collaborated to develop a metasurface “camera lens” for imaging-based measurements of a photon’s quantum state. On the other, an Israeli research team created a metasurface capable of entangling individual photons’ spin and orbital angular-momentum states as the laser light passes through it. Both research groups see significant potential in using dielectric surfaces to solve quantum-optical problems.

Dielectric metasurfaces are ultrathin surfaces that have been highly engineered and decorated with arrays of subwavelength scattering elements. They’ve received a lot of attention in recent years for their ability to reduce the size of bulk optical elements like lenses drastically. The researchers wanted to see if they could replace the bulk, tabletop-scale beam-splitting optical elements commonly used in experiments to realize quantum interference with the tiny metasurfaces.

To get there, they first modeled a metasurface made up of an array of nanoscale “metagratings” interleaved so that individual elliptical polarization states of an input beam were spread out into a parallel array of output beams. The results, plotted on a Poincaré sphere, can be interpreted as “quantum projections in a multiphoton Hilbert space.”  quantum optics metamaterials.”

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