The optical "spin-orbit" coupling occurring in a suitably patterned nonuniform birefringent plate known as `q-plate' allows entangling the polarization of a single photon with its orbital angular momentum (OAM). This process, in turn, can be exploited for building a bidirectional "spin-OAM interface", capable of transposing the quantum information from the spin to the OAM degree of freedom of photons and \textit{vice versa}. Here, we experimentally demonstrate this process by single-photon quantum tomographic analysis. Moreover, we show that two-photon quantum correlations such as those resulting from coalescence interference can be successfully transferred into the OAM degree of freedom.
@article{arxiv.0810.2417,
title = {Quantum information transfer from spin to orbital angular momentum of photons},
author = {Eleonora Nagali and Fabio Sciarrino and Francesco De Martini and Lorenzo Marrucci and Bruno Piccirillo and Ebrahim Karimi and Enrico Santamato},
journal= {arXiv preprint arXiv:0810.2417},
year = {2015}
}