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Proposal for a Quantum Delayed-Choice Experiment

  1. Dec 14, 2011 #1
  2. jcsd
  3. Dec 14, 2011 #2

    DrChinese

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    Re: "Proposal for a Quantum Delayed-Choice Experiment"

    Here is the full paper in the archives:

    http://arxiv.org/abs/1103.0117

    "Gedanken experiments are important conceptual tools in the quest to reconcile our classical intuition with quantum mechanics and nowadays are routinely performed in the laboratory. An important open question is the quantum behaviour of the controlling devices in such experiments. We propose a framework to analyse quantum-controlled experiments and illustrate the implications by discussing a quantum version of Wheeler's delayed-choice experiment. The introduction of a quantum-controlled device (i.e., quantum beamsplitter) has several consequences. First, it implies that we can measure complementary phenomena with a single experimental setup, thus pointing to a redefinition of complementarity principle. Second, a quantum control allows us to prove there are no consistent hidden-variable theories in which "particle" and "wave" are realistic properties. Finally, it shows that a photon can have a morphing behaviour between "particle" and "wave"; this further supports the conclusion that "particle" and "wave" are not realistic properties but merely reflect how we 'look' at the photon. The framework developed here can be extended to other experiments, particularly to Bell-inequality tests. "
     
  4. Dec 15, 2011 #3
    Re: "Proposal for a Quantum Delayed-Choice Experiment"

    From reading the paper, I gather they disprove HV theories that satisfy the two criteria they list; (a) reproducing QM statistics and; (b) having particles and waves as realistic.

    However, from the last page in which they say waves produce particle statistics in an open interferometer (without the 2nd beam splitter), and particles producing interference statistics in a closed interferometer (with the 2nd beam splitter) - that is exactly what happens in Bohmian Mechanics, right? I mean, the particle does go along one path, but interference is still observed in a closed interferometer set-up.
     
  5. Dec 15, 2011 #4
    Re: "Proposal for a Quantum Delayed-Choice Experiment"

    I also don't quite get their assumption on the source emitting wave- and particle-like photons. If they're using that assumption to base their proof, there is no substance to it unless you verify the assumption.
     
  6. Dec 15, 2011 #5

    Ken G

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    Re: "Proposal for a Quantum Delayed-Choice Experiment"

    And the paper concludes: "It is only after we interpret the photon data, by
    correlating them with the results of the ancilla, that either a
    particle- or wave-like behaviour emerges: behaviour is in the
    eye of the observer."
    I'm not sure yet of the significance of having "quantum controls" embedded in the apparatus, that seems like a key part of their innovation, but this conclusion is one that I think is generally valid. Indeed, on several other active threads I've been arguing for a more sensible version of "realism" that accounts for exactly this conclusion, and I'm getting the full range of reactions from that's obvious to that's ridiculous!
     
  7. Dec 16, 2011 #6
    Re: "Proposal for a Quantum Delayed-Choice Experiment"

    I honestly don't get the "eye of the observer" comment. Had the ancilla been measured and found in either |0> or |1>, but we don't correlate the data - would we find the particle still to be in a superposition of wave and particle (from the half intensity interference pattern). Daniel did email me back, but never clarified on that point. All I got was "What we mean by “behavior is in the eye of the observer” is that if we consider the data on the system alone, then it is just a reduced-visibility interference pattern. Only by matching with the data from ancilla, we find the characteristic wave or particle -like dependence of relative frequencies of 0 and 1 as functions of the phase phi."
     
  8. Dec 16, 2011 #7

    Ken G

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    Re: "Proposal for a Quantum Delayed-Choice Experiment"

    I don't know exactly what they mean either, but I think the point is that when you look at only part of the outcomes of the experiment, you might gravitate toward one type of explanation of what happened there (be it more particle-like or more wave-like), but if you also look at the ancilla and correlate, you might be surprised to find that a rather different explanation emerges from the complete data. So your idea about "what was the behavior" can be affected by the perspective you take, and how that perspective can be informed in different ways by different aspects of the full data. My own way of saying that is simply the more general observation that in physics, "explanations are not unique."
     
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