How does magnetism work in QM?

[S Beck]

Electrons' spin state is responsible for magnetism inside a magnet. Two magnets interact at a distance, but what about the space between and around the two magnetic objects? In CM there are field lines and vector fields, but what is actually happening at the QM level?

 

[king vitamin]

In quantum mechanics, the values of the magnetic field are uncertain. At every point in space, you may talk about the probability distribution satisfied by the three components of the magnetic field - their average, their variance, etc. There will also be uncertainty relations, say between the components of the magnetic and electric fields.

The classical limit is when these probability distributions are highly peaked about their mean, so you can just ignore them and model the system by the mean magnetic field everywhere.

 

[jtbell]

but what is actually happening at the QM level?

Beware! asking questions like this is likely to lead you down a rabbit hole into a maze of twisty little passages, all alike.