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Entanglement and Concurrence: asking for definitions

  1. Feb 20, 2010 #1
    Hi All

    I would like to know if one can present simple definitions for entanglement and concurrence as well as experimental forms to detect them.


  2. jcsd
  3. Feb 21, 2010 #2
    I think you will not find the exact definition for the “entanglement” because of it is absent. I can point to similar situation with other widely used term – “coherent states” of atom or molecules.

    The problem is that it is very difficult to give exact definition for the term, which physical nature is not clear. There are the cases of entanglement and coherent states (for additional information see arXiv:0706.2488v2 and physics/0401051).

    So, we should at first understand a physical nature of phenomenon, and only than the exact definition of corresponding terms will be possible.

    But now different scientists put in this terms different (his own) sense (which frequently is unknown for readers) and it makes, of course, a great difficulties for discussion, education, etc. But this is natural thing.

    Till now I nothing hear about the “concurrence” term in physics.
  4. Feb 21, 2010 #3
    Consider the interaction of field and atom, whose wave function are correlated mean u cannot separate the wavefunction of atom from the wavefunction of field, hence they are entangle. change in one will automatically bring change in the other.
  5. Feb 21, 2010 #4
    Concurrence seems to be a hot concept nowadays. Quantum computation, quantum optics and correlated fields.

    I think I disagree with you when you say that such terms don't have exact meaning.
    In my opinion, it is a dynamical situation, may be a little like a small war. Those who defend more intensely and with more talent their view point are likely to win and stabilish the winner meaning of these concepts in these names.

    Let try defining "coherent state", in order to exemplify that all that matter is not to be considered a messy thing:

    Coherence is a property which is strongly related to statistic correlation in multiple (two or more) times and multiple points in space. So every quantum state that presents non zero self correlation (be it in time or space) gathers conditions to be called a coherent state. However, in practice, a more restrictive definition is used, in terms of states that a respresented by P distributions which are delta (peak shaped), one may argue.

    Best Regards,

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