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Does this question make sense? Can measuring the spin of one entangled particle 'determine' the polarization of the other?

Kurt Hikes
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  • Answer: no, this question does not make sense. – WillO Apr 26 '19 at 21:01
  • @WillO your comment is incorrect. The question is sensible and the entanglement proposed in the question can happen. – DanielSank Apr 27 '19 at 01:09
  • @DanielSank: My comment is correct regarding the question in the title. States can be entangled; it makes no sense to ask if "properties" are entangled. – WillO Apr 27 '19 at 12:15
  • @WillO I think that's a rather narrow allowance for interpretation of the words, especially since in this case there's an obvious opportunity to explain something to a willing student. Casting that opportunity aside to tell the student "this question makes no sense" is not in the spirit of this site or of good-faith pedagogy. – DanielSank Apr 27 '19 at 17:54
  • @DanielSank : I enthusiastically agree with your general point about encouraging willing students (and I therefore upvoted Arpad's answer, which I think will help such students in the future), but am skeptical of its application to this particular case, for reasons which are probably best expressed in some forum other than a comment box. – WillO Apr 27 '19 at 20:06

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When two particles become entangled, the whole new system will have a common wavefunction that will describe the whole system. This system in your case will have both particles, so this wavefunction will describe both their characteristics, and not just their spins, but all of their characteristics.

So yes, if they are entangled, measuring particle A's spin will have an effect on the measurement on particle B's polarization.

It is not the spin of the particles that is entangled, but it is the whole system of the particles that is entangled, and that includes all the particles' characteristics.

If you entangle two electrons, and put them in a singlet state (spins entangled), and then let one of the electrons through a Stern-Gerlach magnet, this will determine the particle's position depending on its spin. So now one electron's spin is entangled with the other one's position.

You can view this as if any property of one particle with the other's could be entangled, but like I wrote, the whole system is already entangled, all you do is select certain measurements in certain experiments.

Please see here:

Is it only the spin of a particle that can be entangled with another particles spin?

Árpád Szendrei
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  • I like this answer, but I would like it better without the sentence "You can entangle this way any property...", since you've already said (correctly) that properties are not entangled; states are. – WillO Apr 26 '19 at 21:00