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Negative off-diagonal elements in density matrix?

  1. Jan 12, 2012 #1

    zje

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    I have a quick question. I've been trying to search for an answer, but I'm probably looking in the wrong places.

    Is it valid to have negative off-diagonal elements in a density matrix?

    Thanks!
     
  2. jcsd
  3. Jan 12, 2012 #2

    Physics Monkey

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    Sure, just take the density matrix for the state (up - down).
     
  4. Jan 12, 2012 #3

    tom.stoer

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    Of course.

    In diagonal form you can interpret the diagonal elements as probabilities. But in addition you know that all symmetric matrices can be diagonalized via a unitary transformation.
     
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