Single-photon sources constitute one of the crucial enabling technologies for quantum communications, quantum computation, and quantum-enhanced metrology. Typical quantum emitters (QEs) used for realizing single-photon sources feature low emission rates, non-directional emission, and poorly defined polarization properties, characteristics that prevent QEs from being directly used in quantum technologies. By using properly nanostructured environment, i.e., by coupling QEs with nanocavities or nanoantennas, the QE emission characteristics can be improved drastically due to the Purcell effect and properly engineered near-field interactions that determine the far-field radiation properties. Single photons carrying spin angular momentum (SAM), i.e., circularly polarized single photons generated typically by subjecting QEs to a strong magnetic field at low temperatures, are at the core of chiral quantum optics  enabling non-reciprocal single-photon configurations and deterministic spin-photon interfaces. In this talk, I present a conceptually new approach to the room-temperature generation of SAM-coded single photons (SSPs) entailing QE non-radiative coupling to surface plasmons that are transformed, by interacting with an optical metasurface , into a collimated stream of SSPs with the designed handedness. The results of detailed simulations as well as the first experimental results are presented, and their implications for experiments in chiral quantum optics are discussed.
1. P. Lodahl, S. Mahmoodian, S. Stobbe, A. Rauschenbeutel, P. Schneeweiss, J. Voltz, H. Pichler, and P. Zoller, “Chiral quantum optics,” Nature 541, 473–480 (2017).
2. F. Ding, A. Pors, and S. I. Bozhevolnyi, “Gradient metasurfaces: a review of fundamentals and applications,” Rep. Prog. Phys. 81, 026401(2017).