Quantum Entanglement of the Spin and Orbital Angular Momentum of Photons using Metamaterials

Metamaterials have been a major research area for more than two decades now, involving artificial
structures with predesigned electromagnetic properties constructed from deep subwavelength
building blocks. They have been used to demonstrate a wealth of fascinating phenomena ranging
from negative refractive index and epsilon-near-zero to cloaking, emulations of general relativity
effects, and super-resolution imaging, to name a few. In the past few years, metamaterials have
been suggested as a new platform for quantum optics, and several experiments have already been
carried out with single photons. Our upcoming paper in Science shows how we employ a dielectric
metasurface to generate entanglement between spin and orbital angular momentum of single
photons. We demonstrate experimentally the generation of the four Bell states by utilizing the
geometric phase arising from the photonic spin-orbit interaction, and subsequently show nonlocal
correlations between two photons which interacted with the metasurface. These are the first
experiments where entangled photon states are generated by a metasurface, thus paving the way to
the new area of quantum metamaterials.