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Entanglement swapping - any correlation between previous partners?

  1. Jun 9, 2013 #1
    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.
    Last edited: Jun 9, 2013
  2. jcsd
  3. Jun 12, 2013 #2

    correlation created at the momemt of swapping ? or Wormhole creation ?

    Entanglement = Wormholes
    Last edited: Jun 12, 2013
  4. Jun 12, 2013 #3
    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.
  5. Jun 13, 2013 #4
    maybe lose their value after collapse, taking another value afterward, subsenquently values are no intrinsical.

  6. Jun 14, 2013 #5
    That would require extending quantum mechanics, and would possibly hint at a hidden-variables approach.
  7. Jun 14, 2013 #6

    “No man ever steps in the same river twice, for it's not the same river and he's not the same man.”
    ― Heraclitus
  8. Jun 17, 2013 #7
    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.
  9. Jun 17, 2013 #8
    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?
    "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."
    Last edited: Jun 17, 2013
  10. Jun 17, 2013 #9
    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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