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Loophole-free demonstration of nonlocality?

  1. Apr 27, 2012 #1
    Is anyone familiar with Suarez's papers in this area? I've posted his most recent and pertinent papers on the topic below and even though I read them all, I'm still having trouble understanding his arguments:
    Single-photon space-like antibunching

    The "forthcoming publications" include the following:
    "Empty waves", "many worlds", "parallel lives" and nonlocal decision at detection

    Interestingly, the PBR theorem is also mentioned in his most recent paper:
    Decision at the beam-splitter, or decision at detection, that is the question
    Last edited: Apr 27, 2012
  2. jcsd
  3. Apr 30, 2012 #2


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    Very interesting stuff. Shows how these theorems - Bell, PBR, and now Suarez' - are allowing us to home in on things.

    As I see the conclusion of these, the MWI picture is being attacked (although I may have misunderstood that point). He is asserting non-locality, although as I see it the time symmetric interpretations are not affected. Some people call these non-local although I don't usually group them that way. I call the results consistent with quantum non-locality, and the results are certainly what I would have expected. In fact...

    I was surprised to see how closely the "Single-photon space-like antibunching" experiment was to earlier experiments, here is one example:

    Observing the quantum behavior of light in an undergraduate laboratory (2003)

    They already knew that the 25% prediction of a local theory for double detections did not occur, and would be strictly against the quantum picture. This setup used the heralded photon and the beamsplitter as in the newer one, but did not enforce strict spacelike separation. The extension in the newer experiment was the transition from strict timelike to strict spacelike separation, which clarified those differences with the local picture.
  4. Apr 30, 2012 #3
    From the article/reference above:

    I thought the Schrodinger cat paradox (like the Twin paradox in relativity) was resolved before/at the time the paradox was created.

    Both the paradoxes, I thought, we created to illustrate how they could be resolved within the frame work of QM (for Schrodinger cat paradox) or Relativity (for Twin paradox).

    The Schrodinger cat paradox is resolved by the fact that the entanglement (superposition of states) is broken at some point/event after emission from the radioactive decay. We may not know exactly what that point/event is however there is no paradox.

    or alternatively we can say they were never paradoxes, (its a matter of semantics) since they were resolved at the time of creation (or little before).

    Side note: all the paradoxes of relativity were resolved at the time of creation
    Last edited: Apr 30, 2012
  5. May 1, 2012 #4
    I don't think the cat paradox has been resolved at all.
  6. May 1, 2012 #5
    I think that Schrodinger himself knew there was no cat paradox and he brought/made this up just to illustrate (or better understand) entanglement and to go further.....for the same reason the twin paradox was bought up to illustrate (or better understand) relativity and to show that relativity still works and the twin paradox is resolvable within the framework of relativity.

    Schrodinger was, I think, simply trying to bring out the idea that : it is hard to pin down when the entanglement breaks down.

    None of them is a "true" paradox (its a matter of semantics though).

    I am not aware of any "true/real/unsolved" paradox in physics/science, however I am not a physicist/scientist, so maybe true/unresolved paradoxes exist that I am not aware of.
    Last edited: May 1, 2012
  7. May 1, 2012 #6


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    What entanglement in the Schrodinger's cat "paradox"?
  8. May 1, 2012 #7
    the entanglement between the atoms that are emitted from the decaying radioactive substance in the chamber with the cat.

    Martinbn -- what is your point? what is your hypothesis? the conversation can be faster if you were to disclose that.
  9. May 1, 2012 #8


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    My point is that the point of Schrodinger was not to illustrate (or better understand) entanglement, but to show that extrapolating quantum mechanical conlusions to the macro world leads to absurdity.
  10. May 1, 2012 #9


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    Suarez is asking: at what point is the superposition of states decided? Is it done at the point in the apparatus where the beamsplitter appears? Or is it done later, when the final configuation is known and the particle is detected?

    A local realistic approach says that it must be decided at the beamsplitter, and that leads to a contradiction with his experiment (because sometimes a single photon should lead to 2 clicks, sometimes 0, but QM always predicts 1).

    Where I get a bit confused is how the jump is made to non-locality. He uses a chain of logic to get this, but it seems to me that non-realistic interpretations are not ruled out.
  11. May 1, 2012 #10
    well summarized Dr Chinese

    I have not gone over it yet, maybe someone else in the forum might have.
    Last edited: May 1, 2012
  12. May 1, 2012 #11


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    As I understood Suarez is assuming that decision is made at the event of detection. Because there are two spatially separate detectors measurement process is non-local (given results of experiment).
    But if you assume decision is made at beamsplitter his reasoning does not apply.
  13. May 22, 2012 #12
    I don't think non-realism can ever be brought down? I'm still a bit confused but this sentence by him in a paper that just came out today, does make it a bit clearer and is consistent with what you wrote:
    Interestingly, in this quote he appears to suggest that the "pilot wave" inevitably leads to "many worlds" or at least, that Bohmians can't provide good arguments for opposing "many worlds"? He writes:
    Nonlocality at detection and conservation of energy: Was Einstein looking for an "epistemic" interpretation, a "superdeterministic" one, or both?
    Last edited: May 22, 2012
  14. May 22, 2012 #13
    Let me note the following:

    1) For some mysterious reason, Gisin does not claim anything "loophole-free", Suarez does.
    2) It looks like Suarez' articles that you quote are unpublished.

    Furthermore, I don't believe there is any "loophole-free" evidence of nonlocality in Suarez' articles or in the experiment by Gisin e.a. Indeed, even according to Suarez, there is evidence of nonlocality only if we assume "collapse at detectors":

    "As it is well known, according to standard quantum mechanics which detector clicks (the outcome) becomes determined at the detection. In fact, most physicists share this view also referred to as "the collapse of the wavefunction at detection" by the Copenhagen (standard) interpretation. "Outcome's decision at detection" shall be the basic assumption in this paper." (http://lanl.arxiv.org/pdf/1204.1732.pdf )

    I believe this is a loophole in Suarez' reasoning. Let me remind you that
    1) “no positive experimental evidence exists for physical state-vector collapse” (M. Schlosshauer, Annals of Physics, 321 (2006) 112-149))
    2) collapse and unitary evolution (dynamics) of quantum mechanics are mutually contradictory (see, e.g., http://plato.stanford.edu/entries/qt-measurement/ and references there)
  15. May 22, 2012 #14
    I'm still lost why he claims "loophole-free" but the first paper which seems to serve the basis for his arguments is published in Physics Letters A (May 11/12):

    Single-photon space-like antibunching
  16. May 22, 2012 #15
    Yes, but there are no "loophole-free" claims in the published article (I should have said that the preprints signed by Suarez alone are apparently unpublished). As I said, for some reason, Gisin avoids such claims :-) Their joint paper may be the basis for Suarez' arguments, but not for his collapse assumption.
  17. May 23, 2012 #16
  18. May 23, 2012 #17
  19. May 23, 2012 #18
    the authors do not claim....loophole-free...

    i was asking a general question, to understand loopholes, namely - what is the loophole in two-photon (or any entangled particle) experiments? such as in the paper or even in the delayed choice quantum eraser etc.

    the paper says

    "two-photon interference effects can be observed even when the optical paths in the interferometer have very different lengths, and the photons do not arrive at the beam splitter at the same time"

    the interference, it seems, is happening non-locally. what is the loophole (for QE) in such experiments?

    does it have to do with temporal resolution of the coincidence counter?
    Last edited: May 23, 2012
  20. May 23, 2012 #19
    I don't think I have to sort it out - they don't even claim loophole-free evidence of nonlocality, and experts agree that there is no such loophole-free evidence. Suarez does claim such evidence, and I explained why I cannot believe him.

    As for loopholes in general in experiments with entangled particles, there is the detection loophole, locality loophole, and so on.
  21. May 23, 2012 #20


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    I don't see entanglement is being any kind of resolution to the paradoxes of quantum mechanics, except that it shows why we could never observe macroscopic superpositions (DeadCat + LiveCat).
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