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Violation of Bell's inequality

  1. Sep 27, 2009 #1
    Any comments out there on the very recent work done by researchers in Santa Barbara on the Violation of Bell's inequality in Josephson phase qubits? Any comments on why this argues against any hidden variable interpretations? Why would a pre-determined event be ruled out?
  2. jcsd
  3. Sep 28, 2009 #2
    Because you would need infinite hidden variables I think.
  4. Sep 28, 2009 #3


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    Here is the article link:


    The measurement process plays an awkward role in quantum mechanics, because measurement forces a system to 'choose' between possible outcomes in a fundamentally unpredictable manner. Therefore, hidden classical processes have been considered as possibly predetermining measurement outcomes while preserving their statistical distributions. However, a quantitative measure that can distinguish classically determined correlations from stronger quantum correlations exists in the form of the Bell inequalities, measurements of which provide strong experimental evidence that quantum mechanics provides a complete description. Here we demonstrate the violation of a Bell inequality in a solid-state system. We use a pair of Josephson phase qubits acting as spin-1/2 particles, and show that the qubits can be entangled and measured so as to violate the Clauser–Horne–Shimony–Holt (CHSH) version of the Bell inequality10. We measure a Bell signal of 2.0732 plusminus 0.0003, exceeding the maximum amplitude of 2 for a classical system by 244 standard deviations. In the experiment, we deterministically generate the entangled state, and measure both qubits in a single-shot manner, closing the detection loophole. Because the Bell inequality was designed to test for non-classical behaviour without assuming the applicability of quantum mechanics to the system in question, this experiment provides further strong evidence that a macroscopic electrical circuit is really a quantum system.
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  5. Sep 29, 2009 #4
    Thanks for the posting. It seems to me even though QM is a complete description, superdeterminism is not ruled out as a loophole.
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  6. Sep 29, 2009 #5


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    It is hard to imagine experiment that can rule out superdeterminism. It can be only shown to be superfluous.

    Anyways this experiment does not rule out context dependent local variables.
  7. Sep 29, 2009 #6
    What do you mean by context dependent?
  8. Sep 30, 2009 #7


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    I mean that whether there is click in measurement apparatus directly depends from parameters of field in vicinity of measurement event and relative configuration of interacting particles (no other randomness besides context randomness).
    And next QM observable depends from manipulations with particle AND context before detection. Obviously I imply that there is some context in the form of field traveling along the particle - something like pilot wave in Bhomian interpretation but more random.
  9. Sep 30, 2009 #8


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    It is perhaps worth pointing out that that they are not doing anything "new" in this experiment. It is basically a solid-state version of an experiment that has been done before in analogous systems.
    It is very impressive work but the main goal was to demonstrate the "quantumness" of phase qubits, not to test Bell's inequality. If they had found that the inequalities were NOT violated this would have indicated that there was a problem with their system and not with the inequalities since they are so well established and have been tested in many other systems.

    It will take a few more years before solid state systems can compete with optics etc when it comes to experiments that test fundamental QM.
  10. Oct 1, 2009 #9
    Are there other macro scale events that can demonstrate quantum effects?
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