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I have read a bit about the Delayed Choice Quantum Eraser, and the fact it could mean there exists a possible timeless retro-causality mechanism.

So far to me, the results have been paradoxical. But hey, that's QM, right? I will base my questions from a theoretical derivation of the following experiment :

Remember the premises : a photon is emitted by a laser to a double slit (black wall here), the BBO is a Baryum-like material which diffracts the beam into two (from one photon to two, each having double the wavelength of the original), and those two photons are correlated. The prism is used to reroute the photons on proper ways.

From this experiment, if we detect a wave pattern at D0 then idler photon will opt for D2 or D1 (which of slit A or B was used is not determined), and if we detect a particle pattern at D0 then the idler photon will opt for D4 or D3 (D3 = photon used slit B, D4 = photon used slit A).

It is known that the decision the idler photon takes is made faster than light, which is the cause for which some physicists suspect a possible retro-causality bond compatible with reversibility of quantum effects in time, but that's not really what bothers me here.

If we follow the theory, what would happen in the following conditions ?

We redesign the experiment so that with the help of a switch we can route the photon to a non-decidable solution, just as if it acted as a wave, so to either D1 or D2, or to a decidable route solution, as if we could know if it was slit A or B which was taken, by making it arrive in either D3 or D4.

This is done by replacing rapidly, and in real time, the beam splitters BSb and BSa for mirrors, such as the Ma or Mb mirrors, if we want a decidable route, or by removing them, to obtain a non decidable route.

We, of course, modify the experiment so that we delay the idler photon for a time long enough that allows the experimenter to read results from D0 and take actions on the outcome of the experiment before idler photon hits a final detector.

So, in this modified experiment, when the switch is off, the experiment is basically letting the photon route undetermined.

But things change when we switch the button on. At this moment, we force the system to opt for a decidable route by forcing the released photon to hit mirrors then either D4 or D3 and then tell us which slit that was opted.

Questions :

If we see a wave pattern at D0 and we switch on to force a decidable route (particle pattern) what would happen when idler photon hits D3 or D4 ?

If we want to be consistent with the theory shouldn't we say that if wedecideto switch the button on at the first sight of a lightwave pattern, then the system should resolve in only providing us particles patterns ?

If we decide to let go off the first three detected patterns of waves, this means taking no action on the route of the system when they are recorded, and to switch the button on only at the fourth sight of a pattern, then shouldn't we see a wave pattern for the first three shots, and then only a particles pattern for all other shots ?

So you would control the system by the "will of your mind" ? :-/

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# Delayed ChoiceQuantum Eraser: what about decision?

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