I found this PBS video regarding the delayed choice / quantum eraser experiment, which, like all the others I've seen, states that the interference pattern generated by the photons that pass through a quantum eraser apparatus depends upon whether the individual photons are "marked" with the "which-way" path information that identifies which slit they passed through, even though this marking takes place after the "top" photon (the one that does not go through the delayed choice portion of the apparatus) should have already hit the top detector.
My question is, if I fired a single photon through such an apparatus, which is then split into two entangled "twins", does the "top" photon give up its energy to the top detector the moment it hits the detector? Has this been confirmed experimentally?
EDIT: I've found another thread (link here) which seems to address this question partially, and based on my read, it seems that the top photon gives up its energy the moment it strikes the top detector. Further, it seems that the position of the top photon is determined by this initial "hit".
Why is it then that this experiment is touted as an example undermining causality? That doesn't follow at all, since the position of the top photon is determined by its own flight, and is completely independent of the flight of the bottom photon.
Isn't it far more reasonable to say that we simply get information about the flight of the top photon from the flight of the bottom photon? Rather than saying that the position of the top photon is determined by events related to the bottom photon (which cannot be the case, based on my read of the experiment), the bottom photon's path is determined by whether or not the top photon was subject to interference along its flight.