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We have investigated magnetic dipole–dipole interaction in a gas of Bose–Einstein condensed chromium atoms. The shape of the gaseous cloud within the atom trap and during expansion after release from the trap shows an anisotropic deformation that depends on the direction of a homogeneous magnetic field which magnetizes the Cr cloud but leaves the atom trap unchanged. This effect constitutes the observation of magnetostriction in a gas, previously seen only in magnetic solids and liquids. Our results are consistent with the theory of dipolar quantum gases. Being the first experimentally accessible model system to study dipole–dipole interactions in gases, a chromium Bose–Einstein condensate (BEC) opens fascinating perspectives, e.g. for new quantum phases or magnetic ordering of spin-3 multi-component dipolar BECs.

The general features of atom lithography, such as parallel deposition, large exposure area, nanometer resolution and both direct writing and resist based patterning, make it a promising field. A summary of the present state of neutral atom lithography is presented. The methods and results from various groups are discussed. A more in-depth study of three different types of atom lithography undertaken in our group is given.

Instead of using a solid mask to pattern a light beam (optical lithography) we used a mask made of light to pattern a beam of neutral atoms (atom lithography). By making use of two special features of the atom-light interaction we wrote structures with periods below λ/2. In the first approach we inverted the focussing potentials by switching the detuning of the light field during the deposition. The second method uses the fact that atoms with a magnetic substructure in the electronic ground state are strongly sensitive to the polarization of the light field. Both techniques produce sub-100 nm chromium structures in one and two dimensions on silicon substrates.

We have used neutral chromium atoms to write periodic nanometerscale structures in a direct way. We use the force exerted on the induced dipole of the atom in the intensity gradient of an optical standing light field to focus an atomic beam onto a substrate. The generated pattern reflects the symmetry of the optical standing wave.

We have used a self-assembling monolayer of dodecanethiole molecules as the resist for a lithography technique based on a beam of metastable helium atoms. Doses as low as 3 metastable helium atoms per 10 resist molecules are enough to write patterns. The writing mechanism is based on the Penning-ionization-induced changes of the local wetting properties of the surface. An edge resolution of 30 nanometers is demonstrated.

We report on an experimental investigation of coherent optical excitation processes for an atomic two-level system in metastable helium. A simple absolute measure of the excitation probability is obtained from the deflection of an atomic beam, as excited atoms receive an additional momentum corresponding to a single photon recoil. With this method, we investigate the excitation process as a function of laser power, wavefront curvature and interaction time. Rabi oscillations are seen in the center-of-mass motion of an atomic ensemble for small wavefront curvatures, which change to adiabatic transfer produced by a Doppler detuning chirp for large wavefront curvatures. The adiabatic transfer provides a simple method for complete excitation of an atomic two-level system.

We discuss the prospects for a laser-like source of atoms where — in close analogy to the laser, and in close analogy to the recently observed Bose-Einstein condensation—many atoms of an atomic gas occupy a single center-of-mass motional state. We develop a theoretical description borrowing concepts from many-body quantum field theory and laser theory. Our results show threshold behavior, mode competition and Poissonian atom statistics above threshold.

Atom lithography provides a new technology that enables one to write directly nanometer scale structures onto a substrate in a parallel process. With this technique the trajectories of atoms are manipulated by light forces that efficiently focus the atoms in a standing light field produced by a laser. By chosing different standing light field configurations one can write different periodic patterns. Theoretical calculations predict a linewidth of the deposited structures in the range of 10–20 nm. The technique is a parallel, direct and species selective process involving low particle energy that prevents any damage of the substrate.