Spin State Rotation: Understanding Negative Probability?

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SUMMARY

The discussion centers on the concept of spin state rotation in quantum mechanics, specifically examining the behavior of an electron's spin state |+> after a 360° rotation. The user initially miscalculated the probability of measuring the spin up state, arriving at a negative probability of -1 due to neglecting to square the amplitude. The correct probability, after squaring -1, is confirmed to be 1, illustrating a common misunderstanding in quantum probability calculations.

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  • Understanding of quantum mechanics principles
  • Familiarity with quantum state notation (e.g., |+>, |->)
  • Knowledge of probability amplitudes in quantum mechanics
  • Basic grasp of rotation operators in quantum systems
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  • Study the mathematical framework of quantum state rotations
  • Learn about probability amplitudes and their significance in quantum mechanics
  • Explore the implications of negative probabilities in quantum theory
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eoghan
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Hi there!
If I have an electron in the spin state |+> and I rotate it by an angle of 360°, then the state becomes -|+>. Now, if I want to find the probability of measuring the spin up, I have:
P(|+>)=<+|(-|+>)=-1
So after a rotation of 360° I have a negative probability??
 
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Ok.. I found the error! I have to consider the square of -1 which is 1... really a stupid error :blushing:
 

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