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Delayed choice question

  1. Feb 9, 2015 #1
    When you have the delayed choice quantum eraser, and you make it really really big and you put a measuring device just before the prism where the entangled photon will hit (Kim et al experiment). Does that mean that when that measuring device is 1 light year away and the people operating it can change whether or not it is turned on or of. They can decide the past? By turning the device on (and keep it on) they know that a year earlier people did not see an interference pattern?
    Last edited: Feb 9, 2015
  2. jcsd
  3. Feb 9, 2015 #2


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    Staff: Mentor

    The interference pattern is not directly observed in Kim's experiment; it only becomes apparent when the results from both signal and idler photon are combined by the coincidence counter. (The wikipedia description of this experiment and its significance is pretty good). Thus, there is no possibility of seeing or not seeing an interference pattern before the results from all the detectors are available.

    I don't understand exactly where in the experimental setup you're proposing to put the measuring device that you mention above?
  4. Feb 9, 2015 #3
    thanks for the answer, after reading some more i understand what you say but i dont understand why the 2 detectors that have no wich path information create interference paterns wich are out of fase?
    isn't it possible to combine these 2 detectors in one detector somehow with a new setup?
    what i'm basicly aiming at is what if you take kim's expirement but you place 2 detectors at the end of the path of the idler photons, you can either measure them or not (and know where it came from). if you measure them you record the data and if you dont measure them you destroy the data somehow (maybe a prism that directs them to the same detector, it doesnt even have to be turned on). to cause no confusion: in this setup you use kim's setup but without al the d1,d2,d3,d4 detector stuff. Dont you get different results then?
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