Rydberg excitation of Bose-Einstein condensates

Rydberg atoms provide a wide range of possibilities to tailor interactions in a quantum gas. Here, we report on Rydberg excitation of Bose-Einstein condensed 87Rb atoms. The Rydberg fraction was investigated for various excitation times and temperatures above and below the condensation temperature. The excitation is locally blocked by the van der Waals interaction between Rydberg atoms to a density-dependent limit. Therefore, the abrupt change of the thermal atomic density distribution to the characteristic bimodal distribution upon condensation could be observed in the Rydberg fraction. The observed features are reproduced by a simulation based on local collective Rydberg excitations.     

Signatures of gravitational fixed points at the Large Hadron Collider

We study quantum-gravitational signatures at the CERN Large Hadron Collider (LHC) in the context of theories with extra spatial dimensions and a low fundamental Planck scale in the TeV range. Implications of a gravitational fixed point at high energies are worked out using Wilson's renormalization group. We find that relevant cross sections involving virtual gravitons become finite. Based on gravitational lepton pair production we conclude that the LHC is sensitive to a fundamental Planck scale of up to 6 TeV.     

Echo experiments in a strongly interacting Rydberg gas

When ground state atoms are excited to a Rydberg state, van der Waals interactions among them can lead to a strong suppression of the excitation. Despite the strong interactions the evolution can still be reversed by a simple phase shift in the excitation laser field. We experimentally prove the coherence of the excitation in the strong blockade regime by applying an "optical rotary echo" technique to a sample of magnetically trapped ultracold atoms, analogous to a method known from nuclear magnetic resonance. We additionally measured the dephasing time due to the interaction between the Rydberg atoms.     

d-wave collapse and explosion of a dipolar bose-einstein condensate

We investigate the collapse dynamics of a dipolar condensate of 52Cr atoms when the s-wave scattering length characterizing the contact interaction is reduced below a critical value. A complex dynamics, involving an anisotropic, d-wave symmetric explosion of the condensate, is observed. The atom number decreases abruptly during the collapse. We find good agreement between our experimental results and those of a numerical simulation of the three-dimensional Gross-Pitaevskii equation, including contact and dipolar interactions as well as three-body losses. The simulation indicates that the collapse induces the formation of two vortex rings with opposite circulations.     

Effects on the pigment distribution in paint formulations

Modern water-borne paints are applied in different areas ranging from high-gloss lacquers to flat, scrub-resistant interior paints. The pigment volume concentration (PVC) is one key-parameter adjusting the application properties. In this work formulations differing in the type of binder and dispersing agent were investigated by various techniques concerning the distribution of pigments in the liquid paints and films. The structure of the paints was analyzed by Remission Light Spectroscopy (RLS), Disc Centrifugation, Cryo-Replica Transmission Electron Microscopy (Cryo-TEM) and Cryo-Scanning Electron Microscopy (Cryo-SEM). The pigment distribution in the films was examined by means of Atomic Force Microscopy (AFM), TEM and RLS. The tendency of the pigments to form aggregates was found to depend on both: the type of binder and the dispersing agent. Only by adjusting the properties of the binder in combination with common dispersants it is possible to get well distributed TiO₂ particles within the paint. Correlation of application properties e.g. gloss and blocking to the microscopic structure is presented.     

Balancing Transformations for Infinite-Dimensional Control Systems

In order to facilitate model reduction by balanced truncation, we introduce state space transformations that can be used to construct an ℓ₂-balanced realization of a regular, linear input-ouput map with nuclear Hankel-operator directly from the system generators of an arbitrary, given realization. These balancing transformations are based on factors of the Gramians and, for infinite-dimensional systems, they are usually unbounded operators. Subsequently the ℓ₂-balanced realization can be truncated in a non-trivial way to obtain an approximating, finite-dimensional model. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)