Entanglement swapping - any correlation between previous partners?

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  • #1
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Entanglement swapping - any correlation between previous partners?

Is there any correlation between previous partners/group in entanglement swapping?

The question is illustrated with an example below:

Alice has A & B entangled
Bob has C & D entangled

Charlie entangles B & C, which puts/projects A & D into (superposition) entanglement (?),
And breaks the “original” entanglement between A&B and C&D.

Thus, now we have two separately entangled pairs – B&C and A&D

1. Is the above correct?
2. When B and/or C is collapsed and let’s say B comes spin up and C will necessary come spin down (unless the entanglement is not spin anti-correlated). Can we predict the result of the collapse of A&D? I.e. when A is collapsed, can we predict its spin state.
3. Or in other words (same as question 2), would there be any correlation between A & B or C&D?

4. I guess the answer would be NO to question 2 & 3 above, else it would violate Bell's theorem?

Note: we are taking the case of only - spin anti-correlated, pair in the singlet state.
 
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Answers and Replies

  • #2
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7
Entanglement swapping - any correlation between previous partners?

Is there any correlation between previous partners/group in entanglement swapping?

The question is illustrated with an example below:

Alice has A & B entangled
Bob has C & D entangled

Charlie entangles B & C, which puts/projects A & D into (superposition) entanglement (?),
And breaks the “original” entanglement between A&B and C&D.

Thus, now we have two separately entangled pairs – B&C and A&D

1. Is the above correct?
2. When B and/or C is collapsed and let’s say B comes spin up and C will necessary come spin down (unless the entanglement is not spin anti-correlated). Can we predict the result of the collapse of A&D? I.e. when A is collapsed, can we predict its spin state.
3. Or in other words (same as question 2), would there be any correlation between A & B or C&D?

4. I guess the answer would be NO to question 2 & 3 above, else it would violate Bell's theorem?

Note: we are taking the case of only - spin anti-correlated, pair in the singlet state.

correlation created at the momemt of swapping ? or Wormhole creation ?
http://arxiv.org/abs/1306.0533

http://quantumfrontiers.com/2013/06/07/entanglement-wormholes/
Entanglement = Wormholes
 
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  • #3
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405
I am currently in discussion with a few professors over delayed choice entanglement swapping. The issue I've discovered is that if we assume collapse of photons A and D at their measurement we get results inconsistent with those found. I think delayed choice entanglement swapping is just that, entanglement swapping, but we must give up the premise that a macroscopic device collapses the wave function of photons A and D. So, I believe these experiments show more than entanglement, but also macroscopic superposition.

The Asher Peres article who highlights this, back in 1999, goes ahead calculating experimental outcomes as if Victor's measurement was first (when it was second). Having had comprehensive email correspondence with Bernard d'Espagnat, I think what has failed in determining a result in delayed-choice entanglement swapping experiment is the failure to run the equations through an experimental set-up, rather than simply rewriting photons A and B, and C and D, as photons A and D, and B and C entangled (which are mathematically equivalent). E.g. if we have A and B entangled, but write the state down as if B and C are entangled, then 1/8 probability of A and B being |H>|H>, when A and B are entangled as |H>|V> - |V>|H>. So it is a question on when we use the original entanglement state of A and B, versus the swapped entanglement state.
 
  • #4
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7
I am currently in discussion with a few professors over delayed choice entanglement swapping. The issue I've discovered is that if we assume collapse of photons A and D at their measurement we get results inconsistent with those found. I think delayed choice entanglement swapping is just that, entanglement swapping, but we must give up the premise that a macroscopic device collapses the wave function of photons A and D. So, I believe these experiments show more than entanglement, but also macroscopic superposition.
maybe lose their value after collapse, taking another value afterward, subsenquently values are no intrinsical.




.
 
  • #5
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405
maybe lose their value after collapse, taking another value afterward, subsenquently values are no intrinsical.




.
That would require extending quantum mechanics, and would possibly hint at a hidden-variables approach.
 
  • #6
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7
.

“No man ever steps in the same river twice, for it's not the same river and he's not the same man.”
― Heraclitus
 
  • #7
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In hopes of stimulating more discussion (is there a reference to what StevieTNZ is talking about?)....

Doesn't "monogamy of entanglement" imply that if B&C are maximally entangled, then neither can have any entanglement with A or D? I thought otherwise we run afoul of the no-cloning theorem.

Also I know Quantum Discord is a popular topic in some circles as of late. It refers to non-classical correlations that are not due to entanglement. I'm not sure this is applicable to Sen K's question but it might bring up issues along the same lines.
 
  • #8
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7
http://prl.aps.org/abstract/PRL/v110/i21/e210403
"The role of the timing and order of quantum measurements is not just a fundamental question of quantum mechanics"
"we entangle one photon from the first pair with another photon from the second pair. The first photon was detected even before the other was created. The observed two-photon state demonstrates that entanglement can be shared between timelike separated quantum systems"


the two vector formalism fit neatly with that process.

Can a Future Choice Affect a Past Measurement's Outcome?
http://arxiv.org/ftp/arxiv/papers/1206/1206.6224.pdf

https://www.physicsforums.com/showpost.php?p=4053068&postcount=31
https://www.physicsforums.com/showpost.php?p=4053118&postcount=32
https://www.physicsforums.com/showpost.php?p=4056855&postcount=36


-------
but there is the possibility that the photons interchange information at the time of the monogamy creation or like i prefer to say heterogamy (one up, one down) or is an inherent symmetrical process, we need more experimental testing to know.

https://www.physicsforums.com/showpost.php?p=4402245&postcount=135
http://arxiv.org/pdf/1206.4949v2.pdf
"Physical theories are developed to describe phenomena in particular regimes, and generally are valid only within a limited range of scales. For example, general relativity provides an eective description of the Universe at large length scales, and has been tested from the cosmic scale down to distances as small as 10 meters. In contrast, quantum theory provides an eective description of physics at small length scales. Direct tests of quantum theory have been performed at the smallest probeable scales at the Large Hadron Collider, 10-20 meters, up to that of hundreds of kilometers. Yet, such tests fall short of the scales required to investigate potentially signicant physics that arises at the intersection of quantum and relativistic regimes. We propose to push direct tests of quantum theory to larger and larger length scales, approaching that of the radius of curvature of spacetime, where we begin to probe the interaction between gravity and quantum phenomena"
"The tests have the potential to determine the applicability of quantum theory at larger length scales"

Super Physics Smackdown: Relativity vs Quantum Mechanics...In Space
http://www.technologyreview.com/vie...ty-v-quantum-mechanicsin-space/#ixzz2UyZfdG1L
.
Seevinck prefers talk about Monogamy of correlations than monogamy of entanglement.
monogamy at the moment, later they are promiscuos lol......

quantum discord are quantum correlation measure that goes beyond the entanglement paradigm.

then Di Lorenzo ask
Are quantum correlations genuinely quantum?
http://arxiv.org/abs/1205.0878
"It is shown that the probabilities for the spin singlet can be reproduced through classical resources, with no communication between the distant parties, by using merely shared (pseudo-)randomness."
 
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  • #9
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405
Indeed if photons B and C are maximally entangled then A and B aren't.

However, I'm not disputing that fact, as evidently shown by experiments. I'm merely stating that in order for entanglement swapping to be successful in the Xa Ma et al. experiment, we must do away with a 'collapse of the wave function' for photons A and D when they are 'measured' (note the use of the loose term 'measured'). By that I mean the photon is still in superposition of polarisation states H and V, thus so is the macroscopic apparatus.
 

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