= Zeeman sublevel
{c}
A <Zeeman sublevel> is a magnetic-field-resolved component of an angular-momentum level, labeled by its projection <quantum number> $m$. In the weak-field regime, $\Delta E=g\mu_BmB$ for the relevant electronic <angular momentum>, with appropriate modifications for <hyperfine levels>.
For <angular momentum> one, the values $m=-1,0,1$ give three shifts. The states can be degenerate at zero field yet acquire different <energies> in a field. Light <polarization> and <selection rules> control which sublevels a laser addresses. Strong fields can change the angular-momentum coupling, so one cannot extrapolate every weak-field formula indefinitely.
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