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Alternatives to bell's tests?

  1. Jan 13, 2013 #1
    I wonder if there are experiments that are better, at proving entanglement (and better at closing the loopholes), than Bell's tests given that scientists have progressed much since John Bell conducted his famous tests.

    For example:

    a) sending one of the entangled photons through a double slit and showing how the interference pattern is different for entangled vs "non-entanglement" photons.

    Separate Question: Does increasing the signal to noise ratio (i.e. reduction of noise) help in closing the loopholes?
  2. jcsd
  3. Jan 13, 2013 #2


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    There are a lot of interesting variations on the basic spin tests. There are too many varieties to describe, but I will post a link tomorrow. They all share the idea that entangled systems can conserve all kinds of observables.

    Further, the fair sampling loophole was closed over a decade ago with one such experiment. All pairs were sampled.


    "Local realism is the idea that objects have definite properties whether or not they are measured, and that measurements of these properties are not affected by events taking place sufficiently far away1. Einstein, Podolsky and Rosen2 used these reasonable assumptions to conclude that quantum mechanics is incomplete. Starting in 1965, Bell and others constructed mathematical inequalities whereby experimental tests could distinguish between quantum mechanics and local realistic theories1, 3, 4, 5. Many experiments1, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 have since been done that are consistent with quantum mechanics and inconsistent with local realism. But these conclusions remain the subject of considerable interest and debate, and experiments are still being refined to overcome ‘loopholes’ that might allow a local realistic interpretation. Here we have measured correlations in the classical properties of massive entangled particles (9Be+ ions): these correlations violate a form of Bell's inequality. Our measured value of the appropriate Bell's ‘signal’ is 2.25 ± 0.03, whereas a value of 2 is the maximum allowed by local realistic theories of nature. In contrast to previous measurements with massive particles, this violation of Bell's inequality was obtained by use of a complete set of measurements. Moreover, the high detection efficiency of our apparatus eliminates the so-called ‘detection’ loophole."

    Although local realists deny experiments like this one, this is part of the reason the discussion of loopholes is limited to a relatively small group of researchers. They would like to close all of the loopholes simultaneously as the final absolute proof. This step is quite unnecessary, as there is no similar requirement in any other area of physics.

    By the way, one of the authors of this paper (Wineland) won the 2012 Nobel prize in physics for this and other work.

    And yes, the signal to noise ratio is indeed a factor in closing the fair sampling loophole for photons. There is a threshold at which suitable results can be obtained without having 100% matching. This varies according to both the apparatus and the actual results.
  4. Jan 13, 2013 #3
    Great post, thanks DrChinese.

    Entanglement swapping, is another alternative (proof) that comes to mind.

    Look forward to the link

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