I have not read the full article, but usually you need a laser which can produce single photons and which can control their polarisation (Other sources produce

I have not read the full article, but usually you need a laser which can produce single photons and which can control their polarisation (Other sources produce quantum superpositions of having 1 photon, 2 photons, 4 photons, etc. It's a probability distribution containing all those numbers).