Single atoms in a standing-wave dipole trap

We trap a single cesium atom in a standing-wave optical dipole trap. Special experimental procedures, designed to work with single atoms, are used to measure the oscillation frequency and the atomic energy distribution in the dipole trap. These methods rely on unambiguously detecting presence or loss of the atom using its resonance fluorescence in the magneto-optical trap.Comment: 8 pages, 7 figures, submitted to Phys. Rev.

An optical conveyor belt for single neutral atoms

Using optical dipole forces we have realized controlled transport of a single or any desired small number of neutral atoms over a distance of a centimeter with sub-micrometer precision. A standing wave dipole trap is loaded with a prescribed number of cesium atoms from a magneto-optical trap. Mutual detuning of the counter-propagating laser beams moves the interference pattern, allowing us to accelerate and stop the atoms at preselected points along the standing wave. The transportation efficiency is close to 100%. This optical "single-atom conveyor belt" represents a versatile tool for future experiments requiring deterministic delivery of a prescribed number of atoms on demand.Comment: 8 pages, 8 figures, submitted to Applied Physics

Internet-Unterstützung der Lehre

<br

Eine kritische Analyse von Ruschs Theorien zur Bodenfruchtbarkeit als Grundlage für die Bodenbewirtschaftung im Ökologischen Landbau

Auf die in den 50er und 60er Jahren publizierten Theorien zur Bodenfruchtbarkeit von Hans Peter Rusch wird im organisch-biologischen Landbau heute noch Bezug genommen. Zu nennen sind hier der Rusch-Test zur Einstufung der biologischen Qualität der organischen Substanz und von Böden, die Systematisierung des Abbaus organischer Substanz im Boden und der Humusbildung sowie die Flächenkompostierung. Ruschs Lehren zielen auf eine Verbesserung der Bodengare durch effiziente Zufuhr organischer Substanz und Humusbildung sowie auf die Verbesserung der Ausnutzung von Nährstoffen. Gegen den Geist seiner Zeit grenzte sich Rusch von der Mineraldüngung ab und hebt die auch heute unbestrittene Rolle des Humus für die Bodenfruchtbarkeit hervor. Die tatsächliche Bedeutung von Ruschs Nachweismethoden zur Charakterisierung der Abbaubarkeit von Materialien und von mikrobiellen Kennziffern im Boden für die Landwirtschaft ist vermutlich gering und wissenschaftlich nicht belegt. Sein systematischer Ansatz zum Abbau organischer Substanz im Boden, zur Humusbildung und seine daraus abgeleiteten Konsequenzen für das Management von Wirtschaftsdüngern und anderen in der Landwirtschaft anfallenden organischen Materialien sind auch nach heutigen Kenntnisstand nicht zu widerlegen, erfordern aber eine Überprüfung

Contribution of organic farming to conserving and improving biodiversity in Germany – the example avi-fauna

Although it is the aim of organic farming to increase biodiversity, there is little knowledge about the impact of organic farming on birds. From 2001 to 2003, the number of breeding birds was recorded annually on the organic experimental farm of the Institute of Organic Farming (600 ha), and on adjacent conventional and organic farms (60 ha and 40 ha) in Northern Germany. The number of skylark (Alauda arvensis) territories increased considerably after the conversion from conventional to organic farming on the premises of the Institute. Their number remained unvaried on the conventional farm. The highest density of skylark territories was found on the farm which has been under organic management for many years. The number of yellowhammer (Emberiza citronella) territories fluctuated largely in relation to the availability of field margin strips, both on conventional and organic land. During the breeding season aerial hunters (swallows and swifts) and raptors significantly preferred organic fields. Outside the breeding season, densities of raptors (in autumn and in winter), seed-eating birds (in autumn) and insect-eating birds (in autumn) were significantly higher on organic than on conventional fields

Kurzfristige Auswirkungen des Pflugverzichts auf Collembolen- Gemeinschaften des Bodens

Collembolans, a widespread group of soil fauna, could potentially be used as indicators of management changes in (organic) farming systems. Therefore, we studied effects of reduced tillage compared with conventional tillage on collembolan communities in the short term. Results of a two-year field trial showed that collembolan communities are likely influenced by different tillage systems. However, these effects could not be statistically verified. Furthermore, annual variation seems to strongly influence the composition of collembolan communities. We tend to assign these effects to different crops cultivated during our study