Highly polarizable metastable He* (2 3 S) and Ne* (2 3 P) atoms have been diffracted from a 100 nm period silicon nitride transmission grating and the van der Waals coefficients C3 for the interaction of the excited atoms with the silicon nitride surface have been determined from the diffraction intensities out to the 10th order. The results agree with calculations based on the non-retarded Lifshitz formula.PACS numbers: 34.50.Dy, 03.75.BeThe van der Waals (vdW) force between atoms, molecules and solid surfaces is of far reaching importance in many branches of physics, chemistry, and biology [1]. For larger distances, retardation due to the exchange of virtual photons has to be included, while for distances much smaller than the smallest wavelength a non-retarded approach can be used. The theoretical foundations for atom-surface interactions were laid in the pioneering work of Lifshitz [2]. In this case the non-retarded vdW potential has the form −C 3 /l 3 in leading order, where l is the atom-surface separation and C 3 depends on the atom, its electronic state, and on the electronic states of the solid.For groundstate rare gas atoms the C 3 coefficients have recently been measured with good accuracy [3]. Less is known about the van der Waals interactions of electronically excited metastable and Rydberg atoms, in particular the C 3 coefficient is not accurately known. Some time ago, transmission through narrow channels [4] and level shifts in closed or semi-infinite cavities [5,6] have been studied. Recently, inelastic electronic transitions on passage over a metal edge [7] and reflection from surfaces and (reflection) gratings [8] have been measured. Currently there is great interest in these potentials, in particular for metastable helium which is widely used in atom optics [9] as well as in surface physics [10] and for which Bose-Einstein condensation has recently been achieved [11]. The atom-surface van der Waals potentials could soon become relevant in guiding slow metastable rare gas atoms along microstructures [12] or in studying collective effects of Bose-Einstein condensed metastable He* atoms in contact with a surface.From a theoretical point of view atoms in excited states are of particular interest. Their polarizability α is expected to increase as n 7 , with correspondingly much stronger interactions [13]. Therefore it is not obvious whether approximate formulae for the groundstate atom-surface vdW potential are still applicable for excited atoms. Moreover, with the much stronger vdW interaction new effects such as higher multipole coefficients [14] can be expected.In this article, an effective but simple experimental method is used to determine the atom-surface vdW coefficient C 3 for metastable rare gas atoms. It is based on diffraction of an atomic beam from a nanostructured transmission grating with a period of only 100 nm. Modifications in the hierarchy of the intensities of the higher order maxima in the diffraction pattern have been shown to be directly related to the strength C 3 of the atom...

The Gross-Pitaevskii equation has been extremely successful in the theory of weakly-interacting Bose-Einstein condensates. However, present-day experiments reach beyond the regime of its validity due to the significant role of correlations. We review a method of tackling the dynamics of correlations in Bose condensed gases, in terms of noncommutative cumulants. This new approach has a wide range of applicability in the areas of current interest, e.g. the production of molecules and the manipulation of interactions in condensates. It also offers an interesting perspective on the classical-field methods for partly condensed Bose gases.Comment: 5 pages, 1 eps figure, final version for the proceedings of Quantum Challenges 2003, Falenty, Polan

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The stability of a Bose condensed gas with a negative scattering length is studied with regard to the role played by the initial state. A trapped ideal gas ground state is shown to be unstable when the Gross Pitaevskii equation still predicts the existence of a stable state. A possible relation to a recent experimental study of the critical conditions for stability or collapse of a Bose Einstein condensate (Roberts et al 2001 Phys. Rev. Lett. 86 4211) is discussed.

Advances in micro-technology of the last years have made it possible to carry optics textbooks experiments over to atomic and molecular beams, such as diffraction by a double slit or transmission grating. The usual wave-optical approach gives a good qualitative description of these experiments. However, small deviations therefrom and sophisticated quantum mechanics yield new surprising insights on the size of particles and on their interaction with surfaces.