Bloch oscillations of neutral atoms adsorbed on crystalline surfaces

摘要

Early studies in quantum mechanics predict a counter intuitive oscillatory behaviour for particles in periodic potentials when submitted to static forces. Such phenomena, known as Bloch Oscillations (BO), have been observed only in the last two decades, having since been demonstrated in many different physical systems such as electrons in superlattices, cold atoms in optical lattices and photons in photonic crystals. In the present work we theoretically develop a new system to explore the BO phenomena using neutral atoms trapped in accelerated adsorption potentials. We show that particles bound to a surface by the surface-normal van der Waals potential and having energy bands due to the 2D-periodic potential related to the corrugation of the surface, fulfill the requirements for one to explore behaviours of quantum transport, probing Bloch oscillations or doing Wannier-Stark spectroscopy. The surface ions of a crystal are well located around a periodic lattice so that the repulsive interaction is periodic along the surface crystalline axes. Such potentials may be probed by particles, as has been intensively demonstrated in experiments of atomic diffraction on surfaces, and calculations with potential models have shown a good agreement with experimental results. Here we propose the use of such a periodic potential for the study of the atomic wave-function coherent behaviour when submitted to an inertial force, due to the surface acceleration. Our calculations are made for He atoms interacting with a LiF surface. This choice is justified by the fact that such a system has only a few well resolved adsorption levels, and because it has already been studied and good potential models are available in the literature.