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Quantum Information

  1. Dec 10, 2015 #1
    Does anyone know anything about quantum information theory?
    I am reading a text about transmitting quantum states, represented by density matrices, through channels. Here the depolarising channel is defined as the map:

    X: -> (1-p)X + pτ Tr[X]

    which with probability (1-p) maps the state onto itself and probability p maps it onto the maximally entangled state τ.
    Now my question is: Why did the writers choose to insert Tr[X] = 1 (X is density matrix). Why is that important to have? From what I see, it could just as well be omitted. Come to think of it, I am not sure about the role that the trace of the density matrix plays in the process of transmitting signals and measuring. Could anyone clarify?
  2. jcsd
  3. Dec 15, 2015 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
  4. Dec 15, 2015 #3
    Which text are you referring to? Do you meant to write that τ is the maximally mixed state instead of the maximally entangled state?
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