The challenge of designing these guides is that the wire configurations must be planar , ie, mountable on a planar surface, forming a guide about that surface. B is proportional to the field magnitude, and the atom can be confined near a field minimum. When an experiment is sensitive to the phase accumulated by an atom wave during its transport through a waveguide, the existence of higher modes in the guide is problematic. For instance, slight fluctuations in the coupling at the guide entrance can cause a time-dependent admixture of the first excited state that washes out fringes. These depths are achieved by using sub-micron wire spacing, an application of nanolithography to atom optics.
Tight confinement can also lead to control over the strength of interactions between particles.
See a project description of that experiment on Nynke Dekker's homepage .