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Is this experiment possible

  1. Feb 26, 2012 #1
    If we take two pairs of entangled photons (A+B and C+D), and take one from each pair (B and C) and perform a bell-state measurement on them (or another scheme that entangles photons A and D together):

    (a) if the two other photons have not had their wave function collapsed, four-photon entanglement is created: http://arxiv.org/abs/quant-ph/0104047

    (b) if the two photons had been measured, and then a bell state measurement occured (or similiar), a different result is evident (i.e. not the same result as (a)).

    I've seen (b) realised in delayed-choice entanglement swapping, but is there another scheme that would generate different results if measurement had occured before photons A and D became entangled?
  2. jcsd
  3. Feb 27, 2012 #2


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    Keep in mind this rule: ordering of observation does not change the observed results in any discernible fashion.
  4. Feb 29, 2012 #3
    Maybe this is a right topic.

    Some people had the idea, that we could use entangled photons to send an emergency signal once, by deliberately disrupting their entanglement.
    Is is possible to notice somehow, that the link between them is broken, but not break it ourselves?
  5. Mar 5, 2012 #4
    Any opinions about this idea?
  6. Mar 5, 2012 #5
    In short, no.

    If you take a pair of particles, entangle them, then separate them by a large distance and disrupt the entanglement on one side, it would not immediately affect the state of the particle on the other side in any physically measurable way.
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