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I just have a quick question about Quantum Mechanics. It's probably a bit basic but I'm trying to get my head around the off-diagonal Hamiltonian elements of a perturbation. We can assume the unperturbed Hamiltonian to be degenerate.

If I have a Hamiltonian

[tex]H=H_{0}+H'[/tex]

where the perturbation contains off-diagonal elements what physical meaning does that have?

edit: When i say the off-diagonal elements I mean the off-diagonal elements of:

<nr|H'|ns> where r,s represent the degeneracy. Sorry!

I know not having the off-diagonal matrix elements in the perturbation remove the degeneracy (at least to first order in perturbation theory).

If they remain what is the physical meaning? I think it has to do with the various states interating in some way but I'm not sure. Any help on this would be great!

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# Off-Diagonal Hamiltonian elements

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