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[en] Polycrystalline Ag, covered with a nm thin siloxane layer, was irradiated with ultraviolet light in vacuum at 500 K. Ag particles of different aspect ratios, 50-1000 nm in size, formed on the surface, including a small fraction of nanorods. Pressurized water vapor bubbles are created in the subsurface region by hydrogen radicals photo-chemically released by the siloxane layer. They provide the driving force for a diffusive material flux along grain boundaries to the surface. This mechanism was modeled and found to agree with the experimental timescale: approximately 300 h are required for a 1000 nm particle to form.
[en] Ultracold atomic gases are a versatile instrument allowing to study the rich field of many body physics with unprecedented control. Indeed the coupled dynamics is governed by few parameters only, namely temperature, masses of the constituents and the interactions between them. In ultracold gases these interactions are ruled by the s-wave scattering length. Control over this parameter is provided by magnetic Feshbach resonances. The physics involved can be enriched by choosing a mixture of different atomic species with different masses and different quantum statistics i.e. Bose-Fermi mixtures. The lithium-rubidium system is remarkable among these because of its large mass difference. In recent experiments we were able to detect two heteronuclear Feshbach resonances in the 6Li-87Rb system, that now make it possible to study the physics of this rich system in more detail. The characterization of these resonances and further experiments are discussed in this presentation
[en] Trapping and manipulating ultracold atoms and degenerate quantum gases in magnetic micropotentials is reviewed. Starting with a comprehensive description of the basic concepts and fabrication techniques of microtraps together with early pioneering experiments, emphasis is placed on current experiments on degenerate quantum gases. This includes the loading of quantum gases in microtraps, coherent manipulation, and transport of condensates together with recently reported experiments on matter-wave interferometry on a chip. Theoretical approaches for describing atoms in waveguides and beam splitters are briefly summarized, and, finally, the interaction between atoms and the surface of microtraps is covered in some detail
[en] A survey of the physics of ultracold atoms and molecules, taking into consideration the latest research on ultracold phenomena, such as Bose Einstein condensation and quantum computing. This textbook covers recent experimental results on atom and molecule cooling as well as the theoretical treatment. (orig.)
[en] Superconducting microstructures for trapping and manipulating ultracold quantum gases are expected to provide intriguing physical scenarios in which atomic physics and superconductor science converge. In this study, we investigate the impact of the Meissner effect on magnetic microtraps generated by superconducting microstructures. Both numerical simulations and experiments demonstrate that the Meissner effect shortens the distance between the microtrap and the superconducting surface, reduces the radial magnetic-field gradients and lowers the trap depth. Simulations based on the London theory have been carried out to calculate the supercurrent densities in thin-film microstructures. Experiments were done in a recently-built apparatus that loads ultracold 87Rb atomic clouds into a magnetic microtrap generated by a superconducting Nb wire with circular cross section. By monitoring the position of the atomic cloud, we observe how the Meissner effect changes the microtrap parameters. Measurements of the trap position reveal a complete exclusion of the magnetic field from the superconducting wire for T<6 K. For higher T, the magnetic field partially penetrates the superconducting wire and the microtrap parameters become more similar to those expected for a normal-conducting wire.
[en] We report on the observation of collective atomic recoil lasing and superradiant Rayleigh scattering with ultracold and Bose-Einstein condensed atoms in an optical ring cavity. Both phenomena are based on instabilities evoked by the collective interaction of light with cold atomic gases. This publication clarifies the link between the two effects. The observation of superradiant behavior with thermal clouds as hot as several tens of μK proves that the phenomena are driven by the cooperative dynamics of the atoms, which is strongly enhanced by the presence of the ring cavity
[en] We experimentally and theoretically investigate mechanical nanooscillators coupled to the light in an optical ring resonator made of dielectric mirrors. We identify an optomechanical damping mechanism that is fundamentally different to the well known cooling in standing wave cavities. While in a standing wave cavity the mechanical oscillation shifts the resonance frequency of the cavity, in a ring resonator the frequency does not change. Instead the position of the nodes is shifted with the mechanical excursion. We derive the damping rates and test the results experimentally with a silicon-nitride nanomembrane. It turns out that scattering from small imperfections of the dielectric mirror coatings has to be taken into account to explain the value of the measured damping rate. We extend our theoretical model and consider a second reflector in the cavity that captures the effects of mirror back scattering. This model can be used to also describe the situation of two membranes that both interact with the cavity fields. This may be interesting for future work on synchronization of distant oscillators that are coupled by intracavity light fields. (paper)