J.-C. Karam

High resolution electron imaging system for sub-micron sized metastable atom beams produced by Stern–Gerlach interferometry

The method of modulating an atom beam profile by an immaterial magnetic mask generated in a Stern–Gerlach interferometer is recalled. A special magnetic configuration aimed at producing a single central bright interference fringe (atomic spot) was used. The effects of velocity spread, source coherence and source size on the limiting spot size at large values of the magnetic gradient are discussed. The observation of such small sizes requires a high spatial resolution of the position-sensitive detector. A new electron optical device is described, which images the secondary electron source generated by the impact of the atomic beam on a metallic electrode (detection in real time). Magnifications as high as 65 are accessible, leading to a better than 100 nm resolution of the atomic beam profile when a position-sensitive detector of a few µm resolution is used. Geometric and chromatic aberrations are discussed and, according to simulations, they do not significantly deteriorate the resolution.

Motional states of magnetic molecules and their coherent superposition

We study the coherent superposition of motional states in magnetic molecules. The distinct time evolution of each motional state in the presence of an external magnetic field and the dynamics of the molecular rotation are found to be interrelated by a molecular orientation correlation function. The correlation of two distinct molecular orientations is then investigated in terms of a dimensionless time variable and is found to reflect the inertia of the reorientation process. The relative phase in the coherent superposition gives evidence of a continuous redistribution of the interaction energy among the motional states of the superposition. Numerical simulations are provided for the prototypical magnetic molecule O2 in its ground state. Relevance is indicated for experiments on molecular interferometry, coherent control, and quantum information.

Coherent Atom Optics with fast metastable rare gas atoms

Coherent atom optics experiments making use of an ultra‐narrow beam of fast metastable atoms generated by metastability exchange are reported. The transverse coherence of the beam (coherence radius of 1.7 μm for He*, 1.2 μm for Ne*, 0.87 μm for Ar*) is demonstrated via the atomic diffraction by a non‐magnetic 2μm‐period reflection grating. The combination of the non‐scalar van der Waals (vdW) interaction with the Zeeman interaction generated by a static magnetic field gives rise to “vdW‐Zeeman” transitions among Zeeman sub‐levels. Exo‐energetic transitions of this type are observed with Ne*(3P2) atoms traversing a copper micro‐slit grating. They can be used as a tunable beam splitter in an inelastic Fresnel bi‐prism atom interferometer.

Coherent Atom Optics With Fast Metastable Beams: Metastable Helium Diffraction By 1D and 2D Magnetized Reflection Gratings

1D and 2D reflection gratings (Permalloy stripes or dots deposited on silicon), immersed in an external homogeneous static magnetic field, are used to study 1D and 2D diffraction of fast metastable helium atoms He* (23S1). Both the grazing incidence used here and the repulsive potential (for sub‐level m = −1) generated by the magnetisation reduce the quenching effect. This periodically structured potential is responsible for the diffraction in the incidence plane as well as for the diffraction in the perpendicular plane.

Surface-induced vibrational excitation of metastable nitrogen molecules traversing a micro-slit copper grating: a probe of surface profiles

The interaction at mean distance (a few tens up to a few hundreds of a0), i.e. in the van der Waals interaction range, between metastable nitrogen molecules, N2* (A3Σu+), and the slit edges of a micro-slit copper grating depends on both the molecular orientation and the internuclear distance in the molecule. Such an interaction is able to induce rotational and vibrational transitions. Endo-energetic transitions (v → v + 1, v ranging from 5 to 10) are observed by means of a time-of-flight technique combined with an angular distribution measurement. By setting the grating plane at an angle with respect to the incident direction, different from that imposed by ideally planar slit walls, it is shown that the angular distribution of the inelastic process reveals a departure of the surface from an ideal plane. Assuming a regular evolution of the tangent plane along the surface profile, a mean wall profile can be derived from this distribution.

Production of a ‘natural’ metastable nozzle beam: Van der Waals–Zeeman atomic levels near a metal surface

A method for obtaining a metastable atom beam with properties near to those of a ground state supersonic beam is demonstrated. Calculations on m sublevels of metastable argon near a metal surface are then presented.

Transverse coherence of a natural metastable‐atom nozzle beam : Scattering and van der Waals‐Zeeman transitions

By use of the resonant metastability‐exchange process, a metastable‐atom beam possessing all genuine qualities of a “ natural ” ground‐state atom nozzle beam is prepared. Owing to the angular narrowness (0.35 mrad) and smallness of the effective source diameter (15 μm) of this beam, the scattering of metastable atoms by a silicon‐nitride nano‐slit grating is investigated in detail, in a partially coherent regime. The elastic scattering exhibits high‐order diffraction peaks combined with a standard van der Waals deflection effect. When a static magnetic field is present, surface‐induced exo‐energetic transitions among Zeeman sub‐levels are observed.