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Quantum Entanglement and Communication

  1. Mar 24, 2011 #1
    So i have used the search feature about the topic and found some information. But i couldn't really understand how measuring the properties of one electron and knowing the entangled particles properties can help communication through cosmic distances?

    As i see it, i can not say give a property to a particle. All i can do is just measure it. So where is the control in this? In a process i can't control how can i send information?

    Or maybe the communication and sending information i heard about quantum entanglement was simply a myth?
  2. jcsd
  3. Mar 24, 2011 #2

    Physics Monkey

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    If I understand your post correctly, you have things exactly backwards. Although entanglement implies a kind of non-local correlation between distant objects, it cannot be used to communicate information faster than light across vast distances. Look for quantum no signaling.

    Hope this helps.
  4. Mar 24, 2011 #3

    As I read your post:

    1. You have searched for information on "Quantum Entanglement and Communication."

    2. You have found some.

    3. You disagree with it, and ask if it is a myth.

    IMHO: It is a myth! Your analysis looks OK to me (though I am an engineer, not a physicist).

    I would endorse this response (from Physics Monkey - who is a graduate in physics) 100% by deleting the first sentence (which reads your post somewhaty differently to me):

    "Although entanglement implies a kind of non-local correlation between distant objects, it cannot be used to communicate information faster than light across vast distances. Look for quantum no signaling."

    Hope this helps. And that you see that your analysis is OK (imho). That is: I believe we all agree that your MYTH assessment is correct.

    PS: To be clear on what I mean, using your words: "The communication and sending of information via quantum entanglement (that you heard about) is simply a myth."
    Last edited: Mar 24, 2011
  5. Mar 24, 2011 #4
    I don't think it's a myth I just don't think it is intrinsically understood that well, at least not at a deeply fundamental level. I'd prefer to call it one of the more mysterious aspects of quantum theory.
  6. Mar 25, 2011 #5
    Thank you Gordon, yes you exactly understood what i meant right.

    Calrid well i am a Enterprise Systems Consultant, working in an Integrator Company. So as sending information i instantly start thinking about "0"s and "1"s :)

    With this simple method, i mean using 2 different states of "anything" i can make things talk, walk, dance.. When someone tells me oh you can change the state of a particle, and the other one changes (Which seems false) my brain instantly tells me "What the hell?!"

    I can communicate through billions of light years instantly like that. What happens if i change the twin experiment creating a network between two ships.. etc.

    I agree Calrid we(as humanity) might not have understood this topic fully yet. But i doubt this can be doable, if its doable, oh i will be the first guy buying "0 latency QE Network Cards" trust me.

    No cabling, no signaling the data just travels FTL between two points. That's too good to be true :)
  7. Mar 25, 2011 #6
    There is no signalling faster than light now anyway.

    Quantum cryptography is already in use and the quantum computer chip has already been made in a university in California IIRC. The technology is already here that manipulates qubit states using ion traps. It may be still in its infancy but there's no denying it can be practically used.
  8. Mar 25, 2011 #7
    It is really very simple. It is just not possible to use quantum entanglement for communication. This is proven by the 'no signalling theorem', which says that quantum correlations cannot be used for signalling. The idea is quite easy to grasp. Quantum mechanics is inherently probabilistic, so if you only look at one side of a maximally entangled pair, you just get a random chain of 1 and 0s, with equal probability. The information you can extract from a random chain of 1 and 0 tells you nothing at all about the other system (or anything at all actually), so it is completely useless and might as well be fed to you by a monkey throwing a coin. So you cannot use entanglement to communicate, even though it seems that when one coin is heads, the other one is immediately tails. It is frustrating, I know, but it seems that nature is just determined not to give anybody a free lunch.

    However, this does not mean that you cannot use entanglement in some other capacities. Even though you cannot use entanglement to transmit information directly, you can use entanglement to transmit MORE information then you are able to in the usual sense. I am referring to something called super dense coding. Usually, when you transport a single classical bit from A to B, you can only communicate exactly one bit of information (it is common sense, you give one bit to B, B gains one bit of information). However, it can be shown that if A and B share a quantum bit, then A can, in principle, send over just one (quantum) bit to B, and B will get 2 bits of information! Another exciting thing is of course quantum teleportation, which also requires entangled pairs. So entanglement is indeed a valuable resource still.
  9. Mar 25, 2011 #8
    So if i understood the super dense coding correctly. It is the ultimate way for secure communication?

    Since other than 2 endpoints noone can make anything usefull out of the information sent between these 2 endpoints about the state of the quantum entangled particles they have?
  10. Mar 26, 2011 #9
    Yes, I believe that is correct. As far as I understand it, in order for anyone to retrieve the information, he needs both parts of the two qubit system . Any interception and measurement of one qubit will destroy the quantum correlation, and prevent the original state from being retrieved. However, do note that this is a one way communication. In order to perform a secure 2 way communication, we need to use quantum cryptographical protocols to generate an encryption key for both parties.
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