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I know that two entangled electrons have opposite spins and that the state of one changes the state of the other. The states of electrons I am referring to are spin up and spin down. Is there a practical application of such a phenomenon (like computing, or time travel, etc.). I am not understanding how a dependence of spin between two entangled electrons has any application.

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    $\begingroup$ did you search? for example "entanglement and quantum computations" gives a whole list see arxiv.org/abs/quant-ph/0201143 . time travel is science fiction . $\endgroup$
    – anna v
    Oct 8, 2016 at 6:09

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I know that two entangled electrons have opposite spins and that the state of one changes the state of the other.

There is a misunderstanding here. There are no changes, it is information that changes. Knowledge of the spin of one automatically is knowledge of the spin of the other. If you have two brothers , Dick and Harry, and learn that one is working in in New York and the other in London, ( but your mother does not know who is where) when you meet Dick in New York you immediately know that Harry is in London.

In the quantum framework it is more complicated because the probabilistic nature of quantum mechanical states adds another dimension to the possible correlations, but again it is a matter of previous information formatting knowledge from new observations, not instantaneous transmission of information.

Is there a practical application of such a phenomenon

It is in the research stage for quantum computing, for example this link.

Time travel is science fiction as far as our present physics knowledge base goes.

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  • $\begingroup$ when you say it is previous information, that is what Einstein predicted in his hidden variable throw which was proven wrong in the bell's theorem. $\endgroup$
    – user510
    Oct 8, 2016 at 15:34
  • $\begingroup$ It is mainly conservation laws which generate correlations. That type of information. $\endgroup$
    – anna v
    Oct 8, 2016 at 15:36
  • $\begingroup$ sorry but I am not understanding how quantum computing is using entangled electrons to enhance its computation ability? Could you please explain this $\endgroup$
    – user510
    Oct 8, 2016 at 19:07
  • $\begingroup$ The link given is an example of the state of research. Did you read the abstract? it says :"For any quantum algorithm operating on pure states we prove that the presence of multi-partite entanglement, with a number of parties that increases unboundedly with input size, is necessary if the quantum algorithm is to offer an exponential speed-up over classical computation". Multipartite means "many electrons" entanglement. So according to this entanglement is necessary for quantum computers to be better than usual classical ones. $\endgroup$
    – anna v
    Oct 9, 2016 at 2:46
  • $\begingroup$ yes so I wanted to know what that has to do with spin $\endgroup$
    – user510
    Oct 9, 2016 at 4:08

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