We present a quantitative study of roughness in the magnitude of the magnetic field produced by a current carrying microwire, i.e. in the trapping potential for paramagnetic atoms. We show that this potential roughness arises from deviations in the wire current flow due to geometric fluctuations of the edges of the wire : a measurement of the potential using cold trapped atoms agrees with the potential computed from the measurement of the wire edge roughness by a scanning electron microscope.

We present a detailed model describing the effects of wire corrugation on the trapping potential experienced by a cloud of atoms above a current carrying micro wire. We calculate the distortion of the current distribution due to corrugation and then derive the corresponding roughness in the magnetic field above the wire. Scaling laws are derived for the roughness as a function of height above a ribbon shaped wire. We also present experimental data on micro wire traps using cold atoms which complement some previously published measurements [11] and which demonstrate that wire corrugation can satisfactorily explain our observations of atom cloud fragmentation above electroplated gold wires. Finally, we present measurements of the corrugation of new wires fabricated by electron beam lithography and evaporation of gold. These wires appear to be substantially smoother than electroplated wires.PACS. 39.25.+k Atom manipulation (scanning probe microscopy, laser cooling, etc.) -03.75.Be Atom and neutron optics

Abstract. We describe an atom interferometer to study the coherence of atoms reflected from an evanescent wave mirror. The interferometer is sensitive to the loss of phase coherence induced by the defects in the mirror. The results are consistent with and complementary to recent measurements of specular reflection. Using either dipole forces or magnetic fields, it is not difficult to make a "mirror", i.e. a steep reflecting barrier, strong enough to reflect atoms with velocities of order 1 m/s, the velocity acquired in ∼ 5 cm of free fall. Both dipole and magnetic force mirrors can be coupled with a high quality substrate to guarantee a well defined overall flatness or curvature, thus giving rise to the evanescent wave mirror [2,3], or to the magnetic mirror [4]. It is now well known however, that a fundamental difficulty of atomic mirrors is loss of coherence due to various sources of roughness in the reflecting potential [5,6,7,8]. The extremely small de Broglie wavelength associated with the typical velocities (λ dB ∼ 5 nm in the case of Rb at 1 m/s), imposes severe constraints on the small scale roughness of the substrate -it must be much better than λ dB /2π [9] before the reflection can be considered specular, and therefore coherent. This experiment is the first in which an atomic mirror is used within an interferometer and as such is the first true demonstration of its coherence. PACSIn a previous paper [10], we reported measurements of the velocity distribution of atoms from an atom mirror and measured the fraction of specularly reflected atoms, as well as the transverse velocity profile of the diffusely reflected ones. The resolution of this measurement however, was insufficient to study the lineshape of the specularly reflected distribution -a crucial aspect characterizing the effect of the mirror on the coherence. Here we discuss a a The Laboratoire Charles Fabry is part of the Federation LUMAT, FR2764 du CNRS. related measurement which is able to focus in more detail on the shape of the specularly reflected fraction. We have developed an atom interferometer which gives information complementary to velocity distribution measurements. We observe fringes whose contrast as a function of path difference corresponds to the coherence function of the atomic mirror, in other words to the Fourier transform of the transverse velocity distribution induced by the mirror. This measurement is particularly sensitive to the long distance behavior of the coherence function or to the velocity distribution in the specular peak, where direct velocity distribution measurements are impractical. Narrower velocity selection implies fewer atoms and worse signal to noise. The signal to noise in the interferometric technique is practically independent of the velocity resolution. It is the analog of Fourier transform spectroscopy with de Broglie waves.