Generation of Entangled Photons

diogenes500@gmail.com

Hi,

I'm wondering what the most efficient method to date is for
generating pairs of entangled photons (efficiency being percentage of
pairs created per number of photons input). As far as I can tell
non-linear crystals yields around 10^-9 pairs/input photon, and I find
numbers for production in fibers from 10^-9 to 10^-8 or even 10^-7 (A
theoretical finding I believe, OPTICS EXPRESS, Vol. 12, No. 14 , 3086
). Anyone know what the correct numbers are? Better processes than
non-linear crystals or fibers? The (realistic) upper limit for
crystal/fiber generation or any other method? Also, if you know it, a
citation would be wonderful.

Thanks.