Speed of transmission in quantum entanglement

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Main Question or Discussion Point

speed of "transmission" in quantum entanglement

when we "collapse the wave-function" via observing one of the entangled photons:

is the transfer of the collapse information instantaneous (to the twin photon) or a few/many orders of magnitude of speed of light?

lets say we observe one of the entangled photons (A) to be spin up.

we know that the other photon (B) will be spin down. let's say both the photons are (time-space) separated by 10 light years.

how long does it take for photon B to be spin down (collapse into a definite state) once photon A has been observed to be spin up?


is the "transmission of the wave function collapse from one photon to its twin photon" instantaneous
or
so fast that it appears to be instantaneous?

in other words how fast does the collapse of the wave function travel in a "bi-photon"?
 
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  • #2
ZapperZ
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is it not instantenous but a few/many orders of magnitude of speed of light?

just like, in earlier times, people must have thought that speed of light is instantenous till Mr Morley and his contemporaries.....
This is beginning to verge on a being a bunch of noise. What is it that you are asking here?

And what does the Morley-Michaelson experiment has anything to do with light being "instantaneous"? Even before Relativity, classical E&M never claimed that "speed of light is instantaneous"!

Zz.
 
  • #3
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The way I understand it, the results in spin-correlation experiments are always correlated, regardless of space-like separation between measurements, and regardless of taking into account questions of simultaneity. All that remains when measurements are compared is that their spins are correlated.

Like I said, this is how I know it to be, but if it is otherwise I would like to hear about it.
 
  • #4
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I don't believe information can actually be extracted from the system so such a question is irrelevant. As jfy4 said, only their spins are correlated.
 
  • #5
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when we "collapse the wave-function" via observing one of the entangled photons:

is the transfer of the collapse information instantaneous (to the twin photon) or a few/many orders of magnitude of speed of light?

lets say we observe one of the entangled photons (A) to be spin up.

we know that the other photon (B) will be spin down. let's say both the photons are (time-space) separated by 10 light years.

how long does it take for photon B to be spin down (collapse into a definite state) once photon A has been observed to be spin up?


is the "transmission of the wave function collapse from one photon to its twin photon" instantaneous
or
so fast that it appears to be instantaneous?

in other words how fast does the collapse of the wave function travel in a "bi-photon"?
You seem to be assuming that "collapse of the wave function" refers to some physical event at the level of quantum phenomena. There's no particular reason to assume this.

Some people do assume it, but, my guess is that most don't. "Collapse of the wave function", for most I think, just refers to the registration of a detection, at which point you might or might not be able to say something about the probability of detection of an entangled particle, depending on the settings of the filters.

So, bottom line, you're making a mistake that most of us are cautioned to avoid at the beginning of our qm educations. You're assuming that quantum states correspond to real, physical states. And nobody has any way of knowing how the mathematical formalism of quantum states corresponds to real, physical states.
 
  • #6
DevilsAvocado
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San K, I’ve taken the liberty to edit you OP where it goes 'wrong':
when we "[STRIKE]collapse[/STRIKE] the wave-function" via observing one of the entangled photons:

is the transfer [STRIKE]of the collapse information[/STRIKE] instantaneous (to the twin photon) or a few/many orders of magnitude of speed of light?

lets say we observe one of the entangled photons (A) to be spin up.

[STRIKE]we know that the other photon (B) will be spin down[/STRIKE]. let's say both the photons are (time-space) separated by 10 light years.

how long does it take for photon B to be [STRIKE]spin down (collapse[/STRIKE] into a definite state) once photon A has been observed to be spin up?


is the "[STRIKE]transmission of the[/STRIKE] wave function [STRIKE]collapse[/STRIKE] from one photon to its twin photon" instantaneous
or
so fast that it appears to be instantaneous?

in other words how fast does [STRIKE]the collapse[/STRIKE] of the wave function ('travel') in a "bi-photon"?
  • First, no usable information is exchanged in EPR-Bell experiments.

  • Second, the notions on wavefunction collapse depend on QM interpretation.

  • Third, only in cases where we have so-called 'perfect correlations' could the spin of B be exactly predicted (if A is measured first).

  • Fourth, we don’t know the exact speed of QM influences between A & B, and this builds on the assumption that non-locality is an established fact, which is not finally settled (it could be non-realism instead). However, here’s a paper which sets a lower bound for the speed of the influence to 10,000 x speed of light.
http://www.nature.com/nature/journal/v454/n7206/full/nature07121.html

Testing the speed of ‘spooky action at a distance’
Daniel Salart, Augustin Baas, Cyril Branciard, Nicolas Gisin & Hugo Zbinden
Nature 454, 861-864 (14 August 2008)

... It is still possible that a first event could influence a second, but the speed of this hypothetical influence (Einstein’s ‘spooky action at a distance’) would need to be defined in some universal privileged reference frame and be greater than the speed of light. Here we put stringent experimental bounds on the speed of all such hypothetical influences. We performed a Bell test over more than 24 hours between two villages separated by 18 km and approximately east–west oriented, with the source located precisely in the middle. We continuously observed two-photon interferences well above the Bell inequality threshold. Taking advantage of the Earth’s rotation, the configuration of our experiment allowed us to determine, for any hypothetically privileged frame, a lower bound for the speed of the influence. For example, if such a privileged reference frame exists and is such that the Earth’s speed in this frame is less than 10-3 times that of the speed of light, then the speed of the influence would have to exceed that of light by at least four orders of magnitude.
 
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  • #7
DevilsAvocado
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...All that remains when measurements are compared is that their spins are correlated.
If you define one of the major and maybe most 'irritating' phenomena in QM as "All that remains", it’s okay by me! :wink:
 

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