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Macro entanglment

  1. Nov 27, 2003 #1

    wolram

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    http://www.nature.com/nature/links/010927/010927-2.html

    Particles small enough for their behaviour to be governed by the laws of quantum mechanics can exhibit a remarkable property known as entanglement. A pair of quantum particles can exist in entangled 'superposition', a mixture of states that resolves only when some physical property such as spin or polarization is measured. Quantum entanglement is a fundamental requirement for quantum computing, but until now it has been possible only to generate entanglement between microscopic particles. Using a new method of generating entanglement, an entangled state involving two macroscopic objects, each consisting of a caesium gas sample containing about 1012 atoms, has now been created. The entangled spin state can survive for 0.5 milliseconds, a long time in this context, bringing practical applications of quantum memory and quantum teleportation a little closer.
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    anyone have more on this? like how.
     
  2. jcsd
  3. Nov 28, 2003 #2

    wolram

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    i always thought that when it came to the real nitty gritty
    that you would all cop out, well shame on you.
     
  4. Nov 28, 2003 #3

    chroot

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    What?

    - Warren
     
  5. Nov 28, 2003 #4

    wolram

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    i need an explanation of how if this is correct it fits in
    with current theories, it seems to violate the information
    law, i keep telling you im a pleb so an educated perspective
    of how this violation is wrong would be much apreciated.
     
  6. Nov 28, 2003 #5

    chroot

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    What "information law?"

    - Warren
     
  7. Nov 28, 2003 #6

    jcsd

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    I'm confused this isn't a violation of anything, it's a natural extension of quantum mechanics. You may of heard of decoherence before that this doesn't limit the size of many particle-entangled suystems it just makes them difficult to obtain in practice.
     
  8. Nov 28, 2003 #7

    FZ+

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    If you are refering to the light speed barrier, this doesn't break it, as no information may be passed this way. The entangled state simply allows the change of the first quantum dot from measurement to cause a simultaneous change in the second - but these changes constitute a change from one random state to another random state, and so carry no information.
     
  9. Nov 28, 2003 #8
  10. Nov 29, 2003 #9

    wolram

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    http://www.nsf.gov/pubs/2000/nsf00101/nsf00101.htm#intro



    Since entanglement cannot be created locally, an entangled state shared by two widely separated parties can be a valuable resource (Fig. 3). One application of shared entanglement is a novel quantum communication protocol called quantum teleportation. If one party (Alice) possesses a qubit in an unknown state, she cannot observe the state without disturbing it. But if she shares a Bell pair with another party (Bob), then Alice can convey a perfect replica of her state to Bob by sending him just two bits of classical information. In the process, the shared Bell pair is consumed, and Alice’s original is destroyed. An odd feature of quantum teleportation is that the unknown state can take values in a continuum; nevertheless, thanks to the pre-existing shared entanglement, Bob needs to receive only two classical bits to recover the perfect replica. This protocol has been convincingly demonstrated in the laboratory.
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    maybe i misunderstand what is said here or it is incorrect
    but to my limited unerstanding it states that information
    can be trasmited via entanglement.
     
  11. Nov 29, 2003 #10

    jcsd

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    No, the important thing about quantum teleportaion is that it needs a clasical communication channel to work, you cannot use the entanglment itself to send information.
     
  12. Nov 29, 2003 #11
    Teleportation and transmission of information

    This is quite correct, since Bob's state is effectively completely random until he receives the two bits of classical information from Alice and performs the appropriate correction.

    Another point is that although the state transferred from Alice to Bob is described by continuous parameters (i.e. it effectively contains an infinite amount of information) this does not mean that Bob can recover an infinite amount of information from the state. Consider the simplest case of the teleportation of a two state system (such as the spin state of a spin-1/2 particle). The most information that Bob can recover is two bits of classical information, which is just the amount of information that Alice has to communicate to Bob in order for the protocol to work in the first place.

    The reason for this is basically the Heisenberg uncertainty principle (although actually it is based on modern variants of this that apply to a wider class of measurements). In order for Bob to extract information from the state, he has to choose an observable to measure and that measurement disturbs the original state, reducing the amount of information he can obtain by further measurements.

    Theorems due to Holevo and Massar and Popescu show that in the usual teleportation scheme, Alice can only transmit one bit of classical information to Bob however Alice might decide to encode the information and however Bob might decide to decode it. However, 2 bits can be transmitted using a protocol called "superdense coding", whereby Alice and Bob actually share another entangled state to start with and Alice encodes information in her half of the state and then transmits it to Bob.
     
  13. Nov 29, 2003 #12
    New kid , first post.

    This is the exact situation I have been trying to get a handle on all day . Not only does the experiment demonstrait non-locality , but also macro scale QE, which if the data is correct represents a major shift in the status of both relativity based locality but also a transition of scales in regards to QM.

    I have been trying to gleen an answer as to the state of vacuume/zero state generation of particle/anti-particle pairs in re entanglement. What say ye?
     
  14. Nov 29, 2003 #13
    Large scale entanglement simply implies large scale isolation.

    All quantum particles are smeared to exactly the extent that their state can not be pinned down by observation. The trick is to be able to verify that macro behavior of the entangled particles without being able to observe any single particles. The experimental apparatus simply sets up a situation where this occurs.
     
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