@article{HaakhHenkel2012, author = {Haakh, Harald Richard and Henkel, Carsten}, title = {Magnetic near fields as a probe of charge transport in spatially dispersive conductors}, series = {The European physical journal : B, Condensed matter and complex systems}, volume = {85}, journal = {The European physical journal : B, Condensed matter and complex systems}, number = {1}, publisher = {Springer}, address = {New York}, issn = {1434-6028}, doi = {10.1140/epjb/e2011-20567-1}, pages = {12}, year = {2012}, abstract = {We calculate magnetic field fluctuations above a conductor with a nonlocal response (spatial dispersion) and consider a large range of distances. The cross-over from ballistic to diffusive charge transport leads to a reduced noise spectrum at distances below the electronic mean free path, as compared to a local description. We also find that the mean free path provides a lower limit to the correlation (coherence) length of the near field fluctuations. The short-distance behaviour is common to a wide range of materials, including semiconductors and superconductors. Our discussion is aimed at atom chip experiments where spin-flip transitions give access to material properties with mesoscopic spatial resolution. The results also hint at fundamental limits to the coherent operation of miniaturised atom traps and matter-wave interferometers.}, language = {en} } @phdthesis{Haakh2012, author = {Haakh, Harald Richard}, title = {Fluctuation-mediated interactions of atoms and surfaces on a mesoscopic scale}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-61819}, school = {Universit{\"a}t Potsdam}, year = {2012}, abstract = {Thermal and quantum fluctuations of the electromagnetic near field of atoms and macroscopic bodies play a key role in quantum electrodynamics (QED), as in the Lamb shift. They lead, e.g., to atomic level shifts, dispersion interactions (Van der Waals-Casimir-Polder interactions), and state broadening (Purcell effect) because the field is subject to boundary conditions. Such effects can be observed with high precision on the mesoscopic scale which can be accessed in micro-electro-mechanical systems (MEMS) and solid-state-based magnetic microtraps for cold atoms ('atom chips'). A quantum field theory of atoms (molecules) and photons is adapted to nonequilibrium situations. Atoms and photons are described as fully quantized while macroscopic bodies can be included in terms of classical reflection amplitudes, similar to the scattering approach of cavity QED. The formalism is applied to the study of nonequilibrium two-body potentials. We then investigate the impact of the material properties of metals on the electromagnetic surface noise, with applications to atomic trapping in atom-chip setups and quantum computing, and on the magnetic dipole contribution to the Van der Waals-Casimir-Polder potential in and out of thermal equilibrium. In both cases, the particular properties of superconductors are of high interest. Surface-mode contributions, which dominate the near-field fluctuations, are discussed in the context of the (partial) dynamic atomic dressing after a rapid change of a system parameter and in the Casimir interaction between two conducting plates, where nonequilibrium configurations can give rise to repulsion.}, language = {en} }