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Delayed Choice Quantum Erasure

  1. Mar 4, 2007 #1
    I had thought up this situation where faster than light data transfer could occur, which turn out to have been thought of before. It is something called the Delayed Choice Quantum Erasure.


    "...Even more surprising was that, if you somehow "erase" the which-path information, the interference pattern reappears! And, perhaps most provocative of all, you can delay the "choice" to "erase" or "observe" the which-path information and still restore the interference pattern, even after the original photon has been "observed" at the primary detector!..."

    When they say reappears, what exactly do they mean? Surely they cannot mean that the pattern rearranges itself right before your eyes? If it somehow were to rearrange itself instantly, this would be faster than light data transfer. You would instantly know whether the user at the other end had erased or read the which-path information. That would be data transfered.

    But I don't think the interference pattern instantly reappears, and that is where I think this will not work. But where am I wrong?

    I am a high school kid who has never taken calculous, or a full physics class, so if it is something obvious, I apologize

    And by the way: hello everyone, i'm new here
  2. jcsd
  3. Mar 4, 2007 #2


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    Science Advisor

    See this thread on the same subject which was posted just a few days ago. The interference pattern is only observed when you correlate one set of photons with the other, just looking at one set of photons on their own you won't see an interference pattern no matter what happens to their entangled "siblings".
  4. Mar 4, 2007 #3
    Thanks for the quick reply. Sorry I didnt search, i didnt know it was a common question.

    I will definitely read that thread
  5. Mar 5, 2007 #4


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    Staff: Mentor

    Well, I wouldn't say that delayed-choice experiments are a common subject here. It just happened that there was a discussion a little while ago. I can't remember any previous discussion, so if there was any it must have been quite a while ago.

    Still, it's a good idea to try a search if there are easily identifiable keywords. You usually get better results than the forum's own search feature, by using Google and restricting the search to this site by using the "site:" operator. For example, you could search on

    delayed choice site:www.physicsforums.com

    Hmmm, that actually turns up a fair number of hits! :smile:
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