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I Is it possible to send information with entanglement?

  1. Jan 5, 2017 #1
    I'm not asking about two way or even repeating communication. Is it possible to entangle particles, keep then entangled and send half of them far away, and delay their choice for an arbitrary amount of time?

    What I'm thinking about is asking a yes or no question: Is there life on Planet X? So I take half the particles and trap them in an entangled state on the probe which goes off at subliminal speeds. When the probe reaches its target, it does its analysis and comes up with a binary answer. From that it either gives the particles one or two slits to finally be released through.

    Back on earth at the same time, the other half of the particles are released and either form an interference pattern or clump based on the behavior of the particles light years away?
  2. jcsd
  3. Jan 5, 2017 #2


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    The simple answer is - no.

    You can't determine the state of the sender so even though its correlated there is no way to determine what was sent.

    Last edited: Jan 6, 2017
  4. Jan 6, 2017 #3


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    To add to bhobba's succinct answer (i.e. NO): :smile:

    1. You can "trap" entanglement and maintain it for a period of time.
    2. Entangled particles, as a general rule, do not form interference patterns. The explanation is fairly technical. Of course, the entangled particle can also be "disentangled" and made to form an interference pattern (but its partner would never know that).
  5. Jan 6, 2017 #4


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    Does that mean that an attempt to force an entangled particle to a particular value ends the entanglement? So we can observe entanglement but not use it to send a signal?
  6. Jan 6, 2017 #5


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    You can steer the system in the sense that you force it to take on a definite value for an observable. But there is no way to force an entangled observable to take on a particular value per se.

    So you could "ask" what is the spin value on a particular basis, and you will observe an outcome (which is a random value). And after that, the pair is no longer entangled on that basis.
  7. Jan 6, 2017 #6
    No, wait, part of my idea seems to have been missed. I'm not thinking about getting any information from the particles themselves or requiring them to remain entangled, it's the literal breaking of the entanglement that I'm talking about capturing.

    I'm not talking about getting any information from an individual particle. I'm talking about thousands of them at once. Entangle them, then hold them in that state until the probe reaches it's destination. (At this point, there is still no way to know anything about paths.)

    The probe has a double slit experiment on board, which it can change to be one slit or two depending on the outcome of it's observations. That's the first time any path information should be available. Then the entangled particles are sent through the slits to form either an interference patter or a clump depending on whether the probe opened one or two slits.

    Shouldn't you get the exact same pattern from the other half of the entangled particles the instant the path information is available to the particles on the probe? If the probe let it's half go through one slit, shouldn't you get a clumping behavior out of it's partners?

    Basically, my question boils down to this:
    What's the difference between this setup and a delayed choice experiment other than the distance and times are scaled way up?
  8. Jan 6, 2017 #7


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    I got your idea the first time. I repeat: Generally, entangled particles do not form interference patterns. The reason is technical and complex. Since there will be no double slit interference in the first place, there is no way to send a message by breaking entanglement and then observing something. A few key points:

    1. There is no physically different outcome if Alice measures before Bob, or vice versa, at least as far as the statistical results appear. Thus there is no way to distinguish Alice sending a message to Bob from Bob sending a message to Alice.

    2. Doing something to Alice's particle does not mean that the same thing happens to Bob's particle. Or vice versa. The only thing you can say is that a measurement of an attribute on one will yield a 100% predictable result of the same attribute on the other. And obviously the order of measurement won't matter in such case.

    3. There are significant differences between this setup and a delayed choice setup. You are trying to send a message (you can't). In delayed choice, the setup is modified AFTER certain things happen, leading to causal ordering issues. That's different.
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