Spin-orbit coupling and Berry phase with ultracold atoms in 2D optical lattices

We show how spin-orbit coupling and Berry phase can appear in two-dimensional optical lattices by coupling atoms' internal degrees of freedom to radiation. The Rashba Hamiltonian, a standard description of spin-orbit coupling for two-dimensional electrons, is obtained for the atoms under certain circumstances. We discuss the possibility of observing associated phenomena, such as the anomalous Hall and spin Hall effects, with cold atoms in optical lattices.Comment: 3 figure

Longitudinal Atomic Beam Spin Echo Experiments: A possible way to study Parity Violation in Hydrogen

We discuss the propagation of hydrogen atoms in static electric and magnetic fields in a longitudinal atomic beam spin echo (lABSE) apparatus. Depending on the choice of the external fields the atoms may acquire both dynamical and geometrical quantum mechanical phases. As an example of the former, we show first in-beam spin rotation measurements on atomic hydrogen, which are in excellent agreement with theory. Additional calculations of the behaviour of the metastable 2S states of hydrogen reveal that the geometrical phases may exhibit the signature of parity-(P-)violation. This invites for possible future lABSE experiments, focusing on P-violating geometrical phases in the lightest of all atoms.Comment: 6 pages, 4 figure

Fictitious Magnetic Resonance by Quasi-Electrostatic Field

We propose a new kind of spin manipulation method using a {\it fictitious} magnetic field generated by a quasi-electrostatic field. The method can be applicable to every atom with electron spins and has distinct advantages of small photon scattering rate and local addressability. By using a $\rm{CO_2}$ laser as a quasi-electrostatic field, we have experimentally demonstrated the proposed method by observing the Rabi-oscillation of the ground state hyperfine spin F=1 of the cold $\rm{^{87}Rb}$ atoms and the Bose-Einstein condensate.Comment: 5 pages, 5 figure

Patterns of long‐term vegetation change vary between different types of semi‐natural grasslands in Western and Central Europe

Questions: Has plant species richness in semi‐natural grasslands changed over recent decades? Do the temporal trends of habitat specialists differ from those of habitat generalists? Has there been a homogenization of the grassland vegetation? Location: Different regions in Germany and the UK. Methods: We conducted a formal meta‐analysis of re‐survey vegetation studies of semi‐natural grasslands. In total, 23 data sets were compiled, spanning up to 75 years between the surveys, including 13 data sets from wet grasslands, six from dry grasslands and four from other grassland types. Edaphic conditions were assessed using mean Ellenberg indicator values for soil moisture, nitrogen and pH. Changes in species richness and environmental variables were evaluated using response ratios. Results: In most wet grasslands, total species richness declined over time, while habitat specialists almost completely vanished. The number of species losses increased with increasing time between the surveys and were associated with a strong decrease in soil moisture and higher soil nutrient contents. Wet grasslands in nature reserves showed no such changes or even opposite trends. In dry grasslands and other grassland types, total species richness did not consistently change, but the number or proportions of habitat specialists declined. There were also considerable changes in species composition, especially in wet grasslands that often have been converted into intensively managed, highly productive meadows or pastures. We did not find a general homogenization of the vegetation in any of the grassland types. Conclusions: The results document the widespread deterioration of semi‐natural grasslands, especially of those types that can easily be transformed to high production grasslands. The main causes for the loss of grassland specialists are changed management in combination with increased fertilization and nitrogen deposition. Dry grasslands are most resistant to change, but also show a long‐term trend towards an increase in more mesotrophic species

Spindynamik von Alkaliatomen in Lichtfeldern

This thesis reports on optically induced spin dynamics of alkali atoms. The experiments are performed both on a "7Li atomic beam and on "1"3"3Cs atoms trapped in a novel dipole force trap. The fictitious magnetic field that acts on alkali atoms in an off-resonant, circularly polarized laser field serves as an efficient tool for spatially localized in-beam and in-trap spin manipulation. In the atomic beam the ground state magnetic moments are prepared by optical pumping and sensitively detected by the fluorescence light. The spin precession induced by a fictitious magnetic field is studied in detail and used to create an in-beam spin-echo. The results clearly demonstrate that both D lines lead to a fictitious field of equal magnitude, yet their dispersive resonance shapes have an opposite sign. As a consequence, the effect of the field is enhanced between the D lines, and reduced on either side of the doublet. The atom trap consists of a far red-detuned standing light wave, oriented vertically and allowing for Stern-Gerlach selection of a magnetic substate. By comparing the trapping of a single substate with the simultaneous storage of all sublevels, the decay of spin polarization that results from photon scattering of trap light is measured. Furthermore it is shown that the fictitious magnetic field can easily induce an in-trap spin precession. The results obtained for the fictitious magnetic field are representative for any alkali species, since this field does not depend on the particular nuclear spin, as long as the detuning of the laser is large compared to the excited state hyperfine splitting. (orig.)SIGLEAvailable from TIB Hannover: RO 6920(1999,3) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Broad-area diode-laser system for a rubidium Bose-Einstein condensation experiment

10.1007/s003400000395APPLIED PHYSICS B-LASERS AND OPTICS714475-48

Manipulation of spin-polarized atoms in an optical dipole-force trap

Ultracold cesium atoms are stored in a novel dipole-force trap, which provides long storage times of spin polarization and facilitates easy Stern-Gerlach selection. The trap consists of a far red-detuned standing light wave, oriented vertically in the field of gravity. By comparing the trapping of a single magnetic substate (F=4, mF=0) with the simultaneous storage of all sublevels, we measure the decay of spin polarization that results from photon scattering of trap light. We furthermore observe spin precession in an optically induced “fictitious magnetic field”

Bose-Einstein condensation into nonequilibrium states studied by condensate focusing

10.1103/PhysRevLett.89.270404PHYSICAL REVIEW LETTERS8927270404