I do understand how quantum entanglement works, but I don't understand how this can help us communicate. Just because you know the value of the other, there's no way to change it (as far as I know), so it would be the same, so you couldn't send a bit. I know there's something I'm missing, but I'd really like to understand this, so it would be very helpful. If you could, please break it down for me and maybe use an example, too. Thanks in advance!

So from what I'm getting from some of the comments, I realize that it's not exactly what I'd imagined, and you can't really send data through entangled particles.

  • $\begingroup$ Does this answer your question? Quantum entanglement faster than speed of light? $\endgroup$ – D. Halsey Sep 25 '20 at 0:50
  • $\begingroup$ No, actually, it does not. Could you please provide an answer of your own if you can? $\endgroup$ – Tyler Selden Sep 25 '20 at 1:00
  • $\begingroup$ en.wikipedia.org/wiki/…. $\endgroup$ – D. Halsey Sep 25 '20 at 1:03
  • $\begingroup$ Okay.... So if I'm understanding this correctly (not likely), then it would be like this: Alice wants to send the number 70, so she encodes her photon to 70% spin. then she entangles it with another and sends that to Bob, who reads it and immediatly knows what Alice wanted to send? $\endgroup$ – Tyler Selden Sep 25 '20 at 1:09

It doesn't. For some reason it's widely believed that entangled particles can be used to communicate faster than light, but that isn't actually true. The no-communication theorem says that even slower-than-light communication via entanglement isn't possible.

The closest thing to "communication with the help of entanglement" that comes to mind is quantum teleportation, which makes it possible to move qubits from point A to point B with only a classical channel from A to B (at a cost of one Bell pair per qubit). There could potentially be situations where this is easier than sending the qubit over a quantum channel. The situations where it might be useful are pretty limited, though, because you still need a quantum channel between A and B to distribute the Bell pairs.

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    $\begingroup$ Your answer is quite correct, but I would add that teleportation is more valuable than you imply at the end. For example, one could use a poor channel repeatedly in order to purify a Bell pair, and then use this high-quality pair to transmit a qubit with high precision. Teleportation-like features are also present in many other fault-tolerant protocols. $\endgroup$ – Andrew Steane Sep 25 '20 at 14:58
  • $\begingroup$ superdense coding is also likely worth mentioning here. Having a pre-shared entangled state, one qubit can be used to transmit two bits of information $\endgroup$ – glS Sep 27 '20 at 11:32

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