arXiv subjects

S. Kraft

Publications and source records attributed to S. Kraft.

25 records · Page 2Linked to original sources

arXiv2002

Bose-Einstein Condensates in Magnetic Waveguides

In this article, we describe an experimental system for generating Bose-Einstein condensates and controlling the shape and motion of the condensate by using miniaturised magnetic potentials. In particular, we describe the magnetic trap setup, the vacuum system, the use of dispenser sources for loading a high number of atoms into the magneto-optical trap, the magnetic transfer of atoms into the microtrap, and the experimental cycle for generating Bose-Einstein condensates. We present first results on outcoupling of condensates into a magnetic waveguide and discuss influences of the trap surface on the ultracold ensembles.

cond-mat.soft↗

arXiv2002

Anomalous Longitudinal Magnetic Field near the Surface of Copper Conductors

We have used ultracold atoms to characterize the magnetic field near the surface of copper conductors at room temperature carrying currents between 0.045 A and 2 A. In addition to the usual circular field we find an additional, 1000 - 10000 times smaller longitudinal field. The field changes its strength periodically with a period of 200-300 um.

cond-mat.soft↗

arXiv2002

Surface Effects in Magnetic Microtraps

We have investigated Bose-Einstein condensates and ultra cold atoms in the vicinity of a surface of a magnetic microtrap. The atoms are prepared along copper conductors at distances to the surface between 300 um and 20 um. In this range, the lifetime decreases from 20 s to 0.7 s showing a linear dependence on the distance to the surface. The atoms manifest a weak thermal coupling to the surface, with measured heating rates remaining below 500 nK/s. In addition, we observe a periodic fragmentation of the condensate and thermal clouds when the surface is approached.

cond-mat.soft↗

arXiv2001

Sympathetic Cooling with Two Atomic Species in an Optical Trap

We simultaneously trap ultracold lithium and cesium atoms in an optical dipole trap formed by the focus of a CO$_2$ laser and study the exchange of thermal energy between the gases. The cesium gas, which is optically cooled to $20 μ$K, efficiently decreases the temperature of the lithium gas through sympathetic cooling. The measured cross section for thermalizing $^{133}$Cs-$^7$Li collisions is $8 \times 10^{-12}$ cm$^2$, for both species in their lowest hyperfine ground state. Besides thermalization, we observe evaporation of lithium purely through elastic cesium-lithium collisions (sympathetic evaporation).

physics.atom-ph↗

arXiv2001

Mixture of ultracold lithium and cesium atoms in an optical dipole trap

We present the first simultaneous trapping of two different ultracold atomic species in a conservative trap. Lithium and cesium atoms are stored in an optical dipole trap formed by the focus of a CO$_2$ laser. Techniques for loading both species of atoms are discussed and observations of elastic and inelastic collisions between the two species are presented. A model for sympathetic cooling of two species with strongly different mass in the presence of slow evaporation is developed. From the observed Cs-induced evaporation of Li atoms we estimate a cross section for cold elastic Li-Cs collisions.

physics.atom-ph↗

arXiv2001

Sympathetic Cooling of Lithium by Laser-cooled Cesium

We present first indications of sympathetic cooling between two neutral, optically trapped atomic species. Lithium and cesium atoms are simultaneously stored in an optical dipole trap formed by the focus of a CO$_2$ laser, and allowed to interact for a given period of time. The temperature of the lithium gas is found to decrease when in thermal contact with cold cesium. The timescale of thermalization yields an estimate for the Li-Cs cross-section.

physics.atom-ph↗

arXiv1997

Characterising a Si(Li) detector element for the SIXA X-ray spectrometer

The detection efficiency and response function of a Si(Li) detector element for the SIXA spectrometer have been determined in the 500 eV to 5 keV energy range using synchrotron radiation emitted at a bending magnet of the electron storage ring BESSY, which is a primary radiation standard. The agreement between the measured spectrum and the model calculation is better than 2%. PACS: 95.55.Ka; 07.85.Nc; 29.40.Wk; 85.30.De Keywords: Si(Li) detectors, X-ray spectrometers, detector calibration, X-ray response, spectral lineshape

physics.ins-det↗