I How does quantum entanglement communication work?

F

Frenemy90210

Specifically do we know how the two parties (photons) involved communicate ? how does the state information transferred. Is it transferred by some waves similar to radio waves ? I somehow still can not believe that its real.
 

phinds

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Specifically do we know how the two parties (photons) involved communicate ? how does the state information transferred. Is it transferred by some waves similar to radio waves ? I somehow still can not believe that its real.
It does not "communicate" in the sense that you seem to mean, and it certainly does not propagate in any physical sense, since to do so it would have to "communicate" at the speed of light or less, whereas entanglement is instantaneous.

Yes, this can be difficult to believe when you first learn about it, but it is quite real and has been verified by many experiments.
 

vanhees71

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Nothing communicates instantaneously according to the best theory we have, which is local, microcausal relativistic QFT. The interactions are local, and the linked-cluster principle holds (see Weinberg, QT of Fields, vol. I). The stronger-than-classical correlations between far distant parts of quantum systems, described by entanglement, are due to the preparation of the system in such an entangled state, which clearly has to be made before the measurement at far distant places. None of the single observers can figure out that his part of the system is entangled with the other. To that end both parties have to take their measurement protocols and compare them to see the correlations, for which you need a "classical channel of communication", i.e., you are again bound by the speed-of-light limit.
 

DrChinese

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The stronger-than-classical correlations between far distant parts of quantum systems, described by entanglement, are due to the preparation of the system in such an entangled state, which clearly has to be made before the measurement at far distant places.
I don't disagree that nothing is communicating instantaneously, which is your key point to the OP. However, any discussion of causality and locality is going to run afoul of interpretations, which obviously is outside this thread (and dreaded). So a quibble... Entanglement can occur after measurement via swapping. See:

Experimental Nonlocality Proof of Quantum Teleportation and Entanglement Swapping
Thomas Jennewein, Gregor Weihs, Jian-Wei Pan, Anton Zeilinger
https://arxiv.org/abs/quant-ph/0201134

"...Alice’s measurement projects photons 0 and 3 into an entangled state after they have been measured."

You and I have previously discussed this, I believe.
 

vanhees71

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Experimental Nonlocality Proof of Quantum Teleportation and Entanglement Swapping
Thomas Jennewein, Gregor Weihs, Jian-Wei Pan, Anton Zeilinger
https://arxiv.org/abs/quant-ph/0201134

"...Alice’s measurement projects photons 0 and 3 into an entangled state after they have been measured."

You and I have previously discussed this, I believe.
Yes, but also there you need entangled states to be prepared before you can "swap the entanglement". By construction a local relativistic microcausal QFT obeys the linked-cluster principle and thus cannot violate causality by construction. It's a mathematical fact, and you can only run into quibbles through wrong interpretations. I have not seen any other interpretation than the minimal statistical interpretation, taking Born's rule seriously and as a vital postulate of Q(F)T.
 

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