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.