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Homework Statement
Part (a): Show probability to transit from state i to j is given by:
Part (b)i: Use answer in part (a) to find probability
Part (b)ii: Use time evolution to find probability
Homework Equations
The Attempt at a Solution
Part (a) was alright, bookwork question on time dependent perturbation theory.
What's interesting was, I got different answers for part (b)i and (b)ii.
Part (b)i
Amplitude of finding particle in state j:
[tex]a_j = \frac{1}{i\hbar}\int V_{ji} exp(\frac{i\Delta E}{\hbar}t) dt[/tex]
In this case, ##\Delta E = 2\mu B##, and since the additional hamiltonian is ##-\mu b \sigma_x##, hence ##V_{ji} = \mu b##.
[tex] a_j = \frac{1}{i\hbar} V_{ij}^{*} \int_0^T exp(\frac{i2\mu B}{\hbar}t) dt [/tex]
[tex] |a_j|^2 = (\frac{b}{B})^2 sin^2(\frac{\mu B l}{\hbar v}) [/tex]
Part (b)ii
The time evolution operator is given by ##U_{(t)} = e^{-\frac{iH}{\hbar}t}## such that ##|\psi_t> = U_t |\psi_0>##.
To find the time evolution operator:
[tex]e^{-\frac{iH}{\hbar}t} = exp(\frac{i\mu B \sigma_z}{\hbar}t) exp(\frac{i\mu b \sigma_x}{\hbar}t)[/tex]
For each of the exponentials, I found them in matrix form:
Now to overlap the desired |-,B> = (0 1) state with evolved state ##|\psi_t>##:
[tex] <-,B|\psi_t> = i sin (\frac{\mu b}{\hbar}t) exp(\frac{-i\mu B}{\hbar}t)[/tex]
Thus, probability is ##sin^2 (\frac{\mu b l}{\hbar v})##