Just for completeness. This is the Dopfer experiment. First for starters:
The two slit experiment is famous and confirmed. Repeatedly shoot a photon at two slits, and an interference pattern will emerge. Which is rather odd, since classically, if you understand that a photon is a particle, it should go trough either one, and you'ld expect to see to two stripes. However, even when shooting one photon, it will end up in the traditional collection of bands you'd expect of interfering waves. The only explanation: the photon passed through both, and interfered with itself.
Now, say you'ld want to confirm that, and observe through which slit a photon went. The ridiculous but true observation is that when you place an observer at one side, the photon will just behave classically and only two bands appear. Hence Quantum Theory, a theory where the photon is in an undetermined superstate, and observers, by observing, collapse it to a state.
The Dopfer experiment above is trivial, a photon is split, in the path above its either observed or not, therefore collapsed to a particle or not, in the path below you'ld expect an interference pattern or two bands. I didn't do any math on it, I assume others did and QT predicts that result.
To me, the strange thing in the Dopfer experiment is the placement of the topmost observer before the double slit. Why would a photon in the path below know anything what happened to a photon in the path above? [I am still reading, welcome to the world of quantum.] That's also called non-locality. Non-locality has been proven often on that splitted photons are correlated, but in the end is just a technical prediction of the theory, its not confirmed there's any form of real entanglement, i.e. some strange 'illusive' immediate non-relativistic connection between the residu of a split photon, that's what the Christian paper is about. One might measure correlation, but that doesn't imply entanglement in the quantum theoretical sense.
The Dopfer experiment is all hearsay, I cannot find the original document, I don't know if she did exactly this experiment, but it is said to be confirmed. I don't believe it, then again, life is weird.
(A weird extension of the Dopfer experiment is that if you'ld make the path above longer, the detector below would know the position of the detector above before it is placed somewhere. I.e. you can detect information in the future, which by induction, can be repeated by coupling multiple devices and would give a phone line into the future, 'a phone to God.')
Okay, my interpretation. Is a photon a wave or a particle, or both, or one of two before/after it collapses? I would say neither, its just something we don't understand, and QT is a simplification which works in most circumstances, like Newton's classical mechanics model works in everyday life. Entanglement doesn't exist, neither does collapse of superpositional states. The above experiment is humbug, and the experiments in the video below, if anything, prove that entanglement doesn't exist. Put in more soft terms: QT is right in it's prediction, but wrong it it's interpretation.
I am no physicist. I was just looking up some background on a paper on Quantum Lambda Calculus.
