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Siberion
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Homework Statement
Consider two spin 1/2 particles interacting through a dipole-dipole potential
[tex]\hat{V} = A\frac{(\hat{\sigma_1} \cdot \hat{\sigma_2})r^2 - (\sigma_1 \cdot \vec{r})(\sigma_2 \cdot \vec{r})}{r^5} [/tex]
If both spins are fixed at a distance d between each other, and at t = 0 one of them is parallel to the radius vector r, whereas the other one is anti-parallel to r, find the first moment when the orientations of the spins have inverted.
(Please note that the wording of the problem doesn't mention what does A nor sigma mean, but I assume A must be a normalisation constant and sigma/2 the corresponding spin operators)
Homework Equations
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Time-dependent Schrödinger equation:
[tex]-\frac{\hbar^2}{2m}\nabla^2\Psi + V(\mathbf{r})\Psi
= i\hbar \frac{\partial\Psi}{\partial t}[/tex]
The Attempt at a Solution
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I don't really know where to start from. This exercise is included in the Identical Particles homework series of my Quantum Mechanics II course. I'm not sure what does "find the first moment" really mean. How can there be "a first moment" when in general all we tan talk about is probabilities of measuring certain observables?
As I have to deal with the time variable, I was guessing it might have something to do with the time-dependent Schödinger equation. I guess the wave function needs to evolve with time, and the orientation of the spins would have to change either continuously or spontaneously. Plus the wave function must be anti-symmetric because we are dealing with fermions... Uhm... I am kind of lost. Any kind of help or reference would be greatly appreciated.