Photons stay entangled despite huge jump in frequency

https://physicsworld.com/a/photons-stay-entangled-despite-huge-jump-in-frequency/

"efficiency of process is 70–80%, unprecedented for single photons... by varying the frequency of the incoming laser beam, the pressure of the gas in the fibre or the nature of the gas itself, it should be relatively trivial to alter the phonon frequency, and thereby to alter the amount by which an incoming photon’s frequency is increased. “Everything is reconfigurable,” explains Russell’s colleague Nicolas Joly. “You don’t need to change anything on the optical table – you just change the bottle of gas underneath"