First experimental generation of correlated photon pairs using natural sunlight as the sole pump source

https://www.eurekalert.org/news-releases/1128476

"requires highly stable, power-hungry laboratory lasers driving nonlinear crystal, overcome ground-collected sunlight's natural instability/ shifting angles utilizing automatic sun-tracking coupled with 20-m optical fiber delivering steady illumination to indoor laboratory... enables quasi-phase matching inside crystal, yielding position-correlated 90.7% visibility rate photon pairs... completely passive light source: no external electrical power/ laser hardware...  remote, space-based, or extreme environmental"