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Spin 1/2 system . in Sakurai quantum mechanics

  1. Nov 27, 2015 #1
    1. The problem statement, all variables and given/known data
    KakaoTalk_20151128_005405253.jpg KakaoTalk_20151128_005404054.jpg

    2. Relevant equations

    This is a passage from Modern Quantum Mechanics by Sakurai ( page 26~27)

    3. The attempt at a solution

    I wonder how i can get 1.4.8 , 1.4.9 equations . and what do they mean?
     
  2. jcsd
  3. Nov 27, 2015 #2

    blue_leaf77

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    They follow from the immediately preceding paragraph. It's mentioned that the probability for a measurement on the ##z## spin from a ##|S_x;+\rangle## state is equal to 1/2 for both up and down ##z## spin. This means the magnitude of the projections from the state ##|S_x;+\rangle## to the eigenstates of ##z## spin, ##|+\rangle## and ##|-\rangle##, must be equal to ##1/\sqrt{2}##.
     
  4. Nov 28, 2015 #3
    Then what is ei*delta
     
  5. Nov 28, 2015 #4

    blue_leaf77

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    The expansion coefficient is in general complex, and that complex exponential is set there to account for this fact, neglecting the overall phase factor as this is not influential for a measurement.
     
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