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Any observable difference between two ensembles described by a same density matrix.

  1. Jul 4, 2010 #1
    For example, a esemble of 50% spin up and 50% spin down electrons, the other of 25% spin up,25% spin down, 25% x direction spin up and 25% x direction spin down. The density matrix is identity matrix for both(correct me if i'm wrong), is there any way to distinguish the two experimentally?
     
  2. jcsd
  3. Jul 4, 2010 #2

    DrChinese

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    Re: Any observable difference between two ensembles described by a same density matri

    I believe that these are fundamentally indistinguishable. I think there was a good quote around this, cannot recall who said this right now.
     
  4. Jul 5, 2010 #3
    Re: Any observable difference between two ensembles described by a same density matri

    Emm..I also think so, but it just feels very peculiar....
     
  5. Jul 5, 2010 #4
    Re: Any observable difference between two ensembles described by a same density matri

    What about QM doesn't feel peculiar? :) I'll see if I can find that quote...
     
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