Why does a magnetic field raise the ground state energy of an electrical particle? I heard a statement that the ground state energy of a electrical particle in a magnetic field is larger than its ground state energy without the magnetic field. 
I just heard this statement. This statement shows an energy shift by a magnetic field. This energy shift is different from Zeeman splitting. 
Maybe I have some mistakes when I quote this statement. And I don't know why the ground state energy is different. I guess it has a quantum origin.
If you have heard a similar conclusion, could you tell me the more details? Mathematics and proofs are much better.
 A: 
I heard a statement that the ground state energy of a electrical particle in a magnetic field is larger than its ground state energy without the magnetic field.

This can be understood in terms of classical theory of particle in a magnetic field. Consider particle circling in a magnetic field. Any slow increase of the magnetic field will be accompanied by eddy-like electrical field, which will act on the charged particle in such a way so that the adiabatic invariant $E/\omega$ will be conserved; here $E$ is kinetic energy and $\omega$ is angular frequency of the circular motion of the particle. Since $\omega$ is proportional to $B$, increasing $B$ increases $\omega$ and since the ratio $E/\omega$ remains constant, kinetic energy $E$ increases too. The energy increase is the work of the eddy-like electric field accompanying the changing magnetic field.
A: There are different factors that modify the ground state energy. The principals are fine and hyperfine structure (http://en.wikipedia.org/wiki/Fine_structure)
(http://en.wikipedia.org/wiki/Hyperfine_structure). 
