Cold atoms near a surface

Two-dimensional systems are of great interest in physics as the celebrated quantum-Hall effects show, which are based on a 2D electron gas. Neutral systems involve thin He films and spin polarized atomic hydrogen in a cryogenic environment, where the successful creation of a 2D quasi-condensate was recently reported. Over the last years, with laser cooling and trapping techniques at hand, several schemes for the preparation of laser cooled atomic 2D gases have been proposed. Low dimensional gases are discussed as keys to achieve high density samples of purely optically cooled atoms, since the reabsorption of scattered photons is greatly suppressed compared to the situation in 3D. On the other hand, by structuring 2D waveguide light fields laterally, very versatile integrated atom optical elements can be realized. We have prepared a quasi-2D gas of argon atoms confined in a planar matter waveguide less than 1 μm away from a reflecting surface. We trap metastable Ar⁺ atoms in the ls₅(J=2) state in a magneto-optical trap. Upon release, they fall towards a gold coated prism surface where an evanescent light field is generated by resonant excitation of surface plasmons in the gold layer. This light field is blue detuned from the 1s₅hArr/2p₉(J=3) transition and hence creates a repulsive potential which slows down the falling atoms.