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How do you get photos to become entangled? And is this even possible, or just a theory?

- Thread starter Natko
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- #1

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How do you get photos to become entangled? And is this even possible, or just a theory?

- #2

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There have been lot of experiments to violate Bell/CHSH inequality starting from the one by Alain Aspect. All of these prove the presence of entanglement by separating the particles over larger and larger distance. So it is not just a theory (at least for most of the scientific community although there are still some who doubt it).

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Can you explain how photons can get entangled by SPDC, as well as the CHSH inequality? I cannot understand the Wikipedia explanation.

There have been lot of experiments to violate Bell/CHSH inequality starting from the one by Alain Aspect. All of these prove the presence of entanglement by separating the particles over larger and larger distance. So it is not just a theory (at least for most of the scientific community although there are still some who doubt it).

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CHSH: CHSH is a revision of the Bell inequality. It technically has nothing to do with quantum mechanics (although it is pretty much always discussed in this context), it is just a contrived inequality that has two assumptions: that space is both real and local. If those assumptions are true, then the inequality must always be less than 2. There are certain types of quantum states (producible by SPDC, among other things) that violate that inequality and thus show that one of the assumptions is false. I suggest you concentrate on the interesting philosophical implications of this, and not the form or derivation of the inequality itself. It is not trivial and is also not terribly satisfying once you work it out.