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Delayed choice quantum eraser question

  1. Nov 12, 2015 #1
    Hello I have a question just out of curiosity...suppose you set up a delayed choice quantum eraser experiment and the technologies were available to super miniaturize your detectors, and instead of having a single double slit you have several double slit walls set up in alignment that are ultra thin (lets say its seven layers thick 1/4" over all) with the detectors set up at different layers. And you can turn these detectors on and off in random sequence at almost the speed of light. So that in one layer the detector would be on in another the detector would be off perhaps in some layer there is no detector. lets say for the sake of argument you had it running continuously with a super high speed camera fast enough to film any changes.

    question.... would you expect to see a single double slit pattern, or a wave pattern or a double slit that (morphs) into a wave pattern and back again? I know this tech doesn't exist... but what if it did?
     
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  3. Nov 12, 2015 #2

    DrChinese

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    To the extent you gain which-slit information, you lose the interference pattern. That can occur anywhere between 0 and 100% (keeping in mind that it takes many trials to create a pattern).
     
  4. Nov 12, 2015 #3
    Maybe I don't understand the experiment completely, I was thinking since the experiment was running continuously and the detectors were going on and off randomly at almost the speed of light, that at some point the photon wave is going to pass through the slits when all the detectors are in (off) position. That in that instant you have to get a wave not a particle.
     
  5. Nov 12, 2015 #4

    DrChinese

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    That's correct. And sometime the photons pass by and get detected. If you could potentially deduce the path of the photon, those trials will produce what you refer to as particle behavior. Depending how you set the detectors to operate, that can vary between 0 and 100% (from one extreme to the other, and mixtures in between).
     
  6. Nov 12, 2015 #5
    The YOU in the experiment (the observer effect) has always made me wonder who's doing the observation. Us or the particle/wave? How does "it", seemingly "
    "know" how to "behave". Is this a byproduct of quantum entanglement? The light can't have a consciousness. The detector doesn't have a consciousness. Its not our consciousness as some experiments seem to indicate. What is the mechanism that delivers this observer information to the particle/wave?
     
  7. Nov 12, 2015 #6

    DrChinese

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    As far as anyone knows, consciousness has nothing to do with it. It is really all about the experimental setup, also referred to as the context. The QM prediction is a function of the context. Some elements of the context may seem out of place, but that is the process of making the prediction. If the setup present during a specific trial could distinguish which-slit information... well, that is a component of the overall context.
     
  8. Nov 12, 2015 #7

    zonde

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    Particle/wave can get to the screen by two paths. In order to tell by which path particle/wave had traveled the two paths have to "mark" particles/waves so that they can be told apart. I suppose that answers your question.

    From your first post it sounds like you believe that detectors are inside the slits. But that is not so. You can't observe photons. You detect it only once at the end of it's path. Then based on the place where you detected it you more or less successfully infer it's paths.
     
  9. Nov 12, 2015 #8

    DrChinese

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    zonde, don't mean to disagree with you as you would normally be correct about this. However, in a double slit experiment, you can mark the photons according to their path. You can do this with a polarizing filter. Polarize the left slit as H>, and the right as V>. You can then distinguish them later if you so desire. Regardless of whether you try to or not, photons marked in this fashion will not form an interference pattern. That is because they are forced to take one path or the other, but not both (which is what creates the interference).
     
  10. Nov 12, 2015 #9
    I know the tech doesn't exist the entire scenario was hypothetical. I imagine you'd get the same result if it was set up in a classical configuration. I also know that is a matter of semantics when scientist say the particle/wave "knows" or "behaves" implying that "it" can make a choice. Removing "consciousness" as pure semantics, the information about whether the wave should collapsed because the detector is detecting or not from my prospective information is exchanged between the two.
     
  11. Nov 12, 2015 #10

    zonde

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    I guess I will have to copy Demystifier's signature as my own. Because what I meant in no way contradicts what you said.
     
  12. Nov 12, 2015 #11

    zonde

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    It's not just the tech, there is not theory that would says you can make piece of electronics that "clicks" when a photons is passing by.

    The only way theoretically and practically how you can tell the photons apart is by "marking" them at the slit as DrChinese described in post #8.
     
  13. Nov 13, 2015 #12
    ok forget polarizing, marking paths, and individual photons at the moment...I'm a novice, I study simply as a hobby and to increase my own knowledge and understanding.
    I admit my own understanding of the double slit comes from reading and watching videos. Some information I have read may not be accurate. So lets deal with the core concept. My hypothetical experiments goal was mostly about the wave function collapse from superposition or conversely it remaining a wave and passing through both slits. My thought was that over time you'd get a strong double slit pattern on your back wall and a weaker banding pattern do to the occasional wave passing through both slits. And if you were to watch my hypothetical video slowed down you'd see a double slit and occasionally you'd see a interference pattern flash across the screen. On a separate note I have a thought as to why the particle/wave seemingly (knows) whether to collapse or not. Could it be the detection equipment itself is causing the collapse by changing the environment the particle/wave is traveling through? Perhaps changing the EM field? let me explain to the best of my understanding. Example,.... detector on EM field fluctuates/ wave is forced to take a position. Detector off,... no EM field change, superposition is maintained and the wave passes through both slips unimpeded and interferes with itself. Like iron fillings on a table,... they lay flat on a table undisturbed (detector off) then introduction of a strong magnet underneath the table (detector on) all the fillings instantaneously stand up in a straight line. So it is not a matter of conscious observer or communication of information or the particle (knowing) anything. I believe its a simple change in environmental condition.
     
    Last edited: Nov 13, 2015
  14. Nov 13, 2015 #13
    That's the reason I said this is all hypothetical (imaginary setup) ....maybe you misunderstood.......this is a thought experiment. So just imagine for a moment that there is away to detect the photon particle and the equipment does exist. What would you expect the results to be zonde?
     
  15. Nov 13, 2015 #14

    bhobba

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    This wave particle stuff is a myth:
    http://arxiv.org/abs/quant-ph/0609163

    It might help you to see a fully quantum analysis of the double slit:
    http://arxiv.org/ftp/quant-ph/papers/0703/0703126.pdf

    Its not a consequence of wave particle duality - its a consequence of the Heisenberg uncertainty relation and the principle of superposition.

    Thanks
    Bill
     
  16. Nov 13, 2015 #15
    Then accurate explanation and description of this particular experiment aren't the norm....... the internet is ripe with misinformation. At least it is for laymen.

     
  17. Nov 13, 2015 #16
    I pretty much stated as much bhobba

    This may be the case, but its not as popular as other information that's available nor is it as widely discussed.
     
  18. Nov 13, 2015 #17

    bhobba

    Staff: Mentor

    Its a bit more subtle than that:
    https://www.physicsforums.com/threads/is-light-a-wave-or-a-particle.511178/
    'So there is no duality – at least not within quantum mechanics. We still use the “duality” description of light when we try to describe light to laymen because wave and particle are behavior most people are familiar with. However, it doesn’t mean that in physics, or in the working of physicists, such a duality has any significance.'

    It actually happens in a number of areas of physics. You have to unlearn stuff as you progress.

    Thanks
    Bill
     
  19. Nov 13, 2015 #18

    DrChinese

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    Your question has been answered: which-slit knowledge eliminates the interference. It has absolutely nothing to do with action of the individual detectors themselves, as I mentioned. For example, placing V and H polarizers over the L and R slits eliminates interference, while placing V and V polarizers over them does not.

    http://arxiv.org/abs/1110.4309

    You are new to the forum, so I will point out to be a bit careful about posting personal hypotheses/theories as per above. Those are not consistent with the rules here. I would strongly recommend you learn more about the subject matter before proceeding further along those lines.

    You also mentioned misinformation on the internet. PhysicsForums attempts to limit references to suitable generally accepted ones so that such misinformation is not presented here.
     
  20. Nov 13, 2015 #19
    I understand...... it is less of a theory than it is A REASONABLE assumption on my part based on available data, assuming that data is correct.

    as I stated before so say I now again..... I may have been (misinformed) so any (reasonable assumption) based on misleading or vague data will subsequently be incorrect.

    That why I posted this thread to get (detailed accurate information) from you and other experts in the field and have it broken down and explained so it can be understood.
     
    Last edited: Nov 13, 2015
  21. Nov 13, 2015 #20

    DrChinese

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    I am not sure how many more references you need on this, hopefully these will help:

    Polarized Light
    http://grad.physics.sunysb.edu/~amarch/ [Broken]

    The essential issue in any double slit setup is whether the light goes through one or both slits. If it goes through both, there will be interference. So any way you wish to specify that the thought experiment is performed, if you use this rule you will know the result. The context immediately before or after the photon goes past the slits or any other portion of the setup does not affect the outcome.
     
    Last edited by a moderator: May 7, 2017
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