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For the manipulation of ultra-cold atoms magnetic fields play an
essential role. As long as the spatial variation of the magnetic
field are much less than the typical atomic length scale an atom
behaves like a neutral particle coupling to the external field by
its total spin only. For highly excited atoms or sufficient high
magnetic field gradients this approximation does not hold. Here
the coupling of the charge of the atomic constituents to the
magnetic field has to be taken into account.
In order to reach this regime experimentally so called atom chips seem to be promising tools. Here current carrying micro-structures generate high gradient magnetic fields. Pushing this setup to its limits one can achieve magnetic fields varying on atomic length scales. Thus charge coupling to the magnetic field should cause significant effects on the atomic structure. From our point of view there are two fundamental field configurations being generated by the atom chip. These are the three-dimensional quadrupole field and the sideguide. We investigate the electronic structure of atoms exposed to the above field configurations. Here, in contrast to the homogeneous field, the spin and spatial degrees of freedom are coupled leading to unique properties of the electronic states. An inspection of the systems symmetries reveals a two-fold degeneracy of the electronic states in the presence of the field. We analyze both low-lying and highly excited states over a broad regime of field gradients. The delicate interplay between the Coulomb and various magnetic interactions leads to complex patterns of the spatial spin polarization of individual excited states. We also study electromagnetic transitions and point out differences to the electromagnetic spectrum observed in a homogeneous magnetic field. Furthermore we show that the three-dimensional magnetic quadrupole field induces a permanent state dependent electric dipole moment of the atom. |