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Homework Help: How can we find the variance of S_x, S_y, and S_z?

  1. Dec 5, 2007 #1
    Given |Psi> = a|up>+b|down>, in principle it should not be so difficult but when I calculate

    Delta S=Sqrt[<S^2_x,S^2_y, or S^2_z>-<S_x,S_y, or S_z>^2]

    the second term gives the problem. Lots of many terms a*, a, b*, b which is not cancelled involve.

    Whoever knows the way to get rid of this problem, please let me know.
  2. jcsd
  3. Dec 6, 2007 #2


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    Can you show what you've tried so far?
    For example, how did you go about finding <S_x>?
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