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Quantum entanglement communication

  1. Mar 28, 2012 #1

    I've been reading some stuff about quantum entanglement and I stumbled upon an article talking about a delayed choice quantum eraser experiment using parametric down conversion. I was wondering if it was possible to communicate a signal through to the other side faster than light. I know that you can't send any information over the channel to the other side faster than light because you don't know which side picked which state, but what if all I'm interested in is that the other side picked any state?

    For example, if Alice is in one room while Bob is in another. Bob tells Alice, "As soon as I force my particle to pick a state, take the clothes to the dry cleaners." In his room, Bob forces his particle to pick a state, while Alice is observing the interference pattern from her photons in her room. As soon as Alice's interference pattern disappears, she knows she's supposed to take the clothes out to the dry cleaners. Now, if Alice was in a different galaxy than Bob, wouldn't Bob have communicated to her to take the clothes to the dry cleaners faster than light?
  2. jcsd
  3. Mar 28, 2012 #2
    I think I might have answered my own question.

    In my example above, the mechanism that I'm suggesting to communicate does work, but it's just that it's actually not faster than light. And the reason is because Bob has to first tell Alice what to do and then go to the other galaxy at slower than light speed. Can I verify that this is correct?
  4. Mar 28, 2012 #3


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    Surprisingly, entangled particles do not produce such interference. See for example:

    Experiment and the foundations of quantum physics, Anton Zeilinger, p. 290, Figure 2.

    So that is issue number 1 here.
  5. Mar 29, 2012 #4
  6. Mar 29, 2012 #5


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    The confusion stems from the fact that there are TWO types of delayed choice experiments.

    Type I involves only one interfering particle, there is no other particle entangled with it. The interference pattern can be seen on the screen, but there is nothing superluminal about it because there is no entanglement.

    Type II involves two entangled particles, where one of them impinges on the screen. The interference pattern is not seen on the screen. Interference is only seen in coincidences through joint measurements of BOTH particles.
  7. Mar 29, 2012 #6

    Thanks for your replies. =) I'm a novice at this stuff, so thanks for your patience. I was wondering, if you take away D3 and D4 and also remove Bsa and Bsb in the quantum eraser experiment in the wikipedia article, would you still get an interference pattern? Thanks in advance for any help you can give. =)

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