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

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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?
 

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  • #2
DrChinese
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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?
I believe that these are fundamentally indistinguishable. I think there was a good quote around this, cannot recall who said this right now.
 
  • #3
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Emm..I also think so, but it just feels very peculiar....
 
  • #4


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

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