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From what I am understanding, there is entanglement in a system if there is a correlation between elements of that system. For an example that I found, If you have only two cards and know that one is red and one is black, if they are both face down and you choose one, by knowing the color of the card just chosen, you know the color of the other card. Hence these cards are 'entangled' (please correct me if I am wrong).

Now this 'correlation/entanglement' seems to be relevent only in respect to some 'reference' knowledge, that is, it is only because we know there is a correlation between cards that we can judge that the other card has to be a particular color. So this comes down, at least in part, to knowledge about the system.

So If I have a logical system, say B = Black and R = Red where upon measurement I have B XOR R where XOR is Exclusive OR, then could I say that B and R are logically entangled over XOR? I say XOR and not OR as we can not not pick (measure) both B and R simultaneously

Furthermore, if I have an equal chance of picking either B or R before measurement would it be correct to say that B and R are in a superposition? That is, the valuation of B and the valuation of R (measuring B to be true [picked] or R to be true [picked]) are in a superposition?


marked as duplicate by Norbert Schuch, Daniel Griscom, user36790, John Rennie, ACuriousMind Jan 17 '16 at 15:48

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    $\begingroup$ "From what I am understanding, there is entanglement in a system if there is a correlation between elements of that system." -- Wrong. (And thus also what follows.) Please use the search function, this has been asked and answered here a million times. $\endgroup$ – Norbert Schuch Jan 16 '16 at 23:52
  • $\begingroup$ Let us continue this discussion in chat. $\endgroup$ – CuriousOne Jan 17 '16 at 3:12

You are absolutely right with the cards. To lift the entanglement on atomistic level talented physicists created the spontaneous parametric down conversation. They solved the task to create pairs of particles (photons) with one entangled parameter. Often this parameter is the direction of the electric field component of the two involved photons. This directions are randomly distribute around the motion direction axis, but always in opposite directions for this two particles. How not to say, that the situation is clearly?

Now the representatives of the quantum mechanics came into the play. They say, that in a situation, one could not measure the states of a system of two (entangled) particles, the states are a superposition and this superposition collapses during a measurement. They strictly ignore the causality of why and how the entangled state of two particles was created. Also they misinterpreting the mathematical expression, which shows the change in the knowledge about the measurement results, into a collapse of the entanglement. This is nonsense. What is right is that we don't know the direction of the electric field because the two photons are not polarized, they are only entangled by the opposite field directions.

To measure the electric field directions we influence and change this direction. But - if we not not changing the detection directions of our measurement instruments (polarizer grids) - we get a coincidence that the talented physicists made there job well.


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