https://www.sciencedaily.com/releases/2019/10/191005134020.htm

A key resource to advance research in quantum information science would be a source that could efficiently and reliably produce single photons. However, because quantum processes are inherently random, creating a photon source that produces single photons on demand presents a challenge at every step.

Now University of Illinois Physics Professor Paul Kwiat and his former postdoctoral researcher Fumihiro Kaneda (now an assistant professor at Frontier Research Institute for Interdisciplinary Sciences at Tohoku University) have built what Kwiat believes is "the world's most efficient single-photon source." And they are still improving it. With planned upgrades, the apparatus could generate upwards of 30 photons at unprecedented efficiencies. Sources of that caliber are precisely what's needed for optical quantum information applications.