Stuttgart 2012 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 42: Ultra-cold atoms, ions and BEC IV

A 42.1: Hauptvortrag

Freitag, 16. März 2012, 10:30–11:00, V57.03

Quantum reflection and matter-wave optics with helium atoms and molecules — •Wieland Schöllkopf — Fritz-Haber-Institut, Berlin

Quantum reflection allows atoms or molecules to be reflected from a solid without colliding with the actual surface. For sufficiently small incident kinetic energy the particle can scatter back at the attractive Casimir-van der Waals potential way in front of the surface. This effect is incompatible with classical physics, but readily explained by quantum mechanics. We have observed non-destructive scattering of He₂ (binding energy 10⁻⁷ eV) from a solid reflection grating. Helium dimers are quantum reflected tens of nm above the surface where the surface-induced forces are too weak to dissociate the fragile bond [1].

In another experiment we applied quantum reflection from a grating to observe emerging beam resonances in an atom-optical diffraction experiment for the first time [2]. This effect, also known as Rayleigh-Wood anomalies, had first been observed in 1902 by R.W. Wood in white-light grating diffraction. Rayleigh found that the anomalies occur when the wavelength and grating period are such that one of the diffraction beams just emerges from the grating surface, causing abrupt intensity variations in the other diffraction beams. Later, the effect was also observed with electrons diffracted from crystal surfaces. Our observation completes the analogy between photon optics and matter-wave optics and might provide a sensitive probe of atom-surface interactions.

[1] B.S. Zhao, G. Meijer, and W. Schöllkopf, Science 331, 892 (2011). [2] B.S. Zhao, G. Meijer, and W. Schöllkopf, PRL 104, 240404 (2010).