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Homework Help: Spin 1/2 particle in |z+> state hits a magnetic field

  1. May 15, 2013 #1
    1. The problem statement, all variables and given/known data

    "A spin 1/2 electron in a hydrogen atom is placed in a time-independent magnetic field B=B0(k)
    The electron's spin starts in the |z+> state at t=0.
    Calculate probability o ffinding the electron in the |y-> state as a function of time for t>0.

    2. Relevant equations

    3. The attempt at a solution

    Basically I'm just confused about what to do about there being a z and y direction. I know how to calculate probabilities for spin states.
  2. jcsd
  3. May 18, 2013 #2
    If you know all these things, you can do it.
    1. Can you write down the Hamiltonian for the system?
    2. Using the Hamiltonian, can you write the time-dependent state of the particle?
    3. Back to basics. What is the projection of the time-dependent state onto |-y>?
    4. If you know the projection, what's the probability?
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