Trapped-ion probing of light-induced charging effects on dielectrics

We use a string of confined $^{40}$Ca$^+$ ions to measure perturbations to a trapping potential which are caused by light-induced charging of an anti-reflection coated window and of insulating patches on the ion-trap electrodes. The electric fields induced at the ions' position are characterised as a function of distance to the dielectric, and as a function of the incident optical power and wavelength. The measurement of the ion-string position is sensitive to as few as $40$ elementary charges per $\sqrt{\mathrm{Hz}}$ on the dielectric at distances of order millimetres, and perturbations are observed for illumination with light of wavelengths as long as 729\,nm. This has important implications for the future of miniaturised ion-trap experiments, notably with regards to the choice of electrode material, and the optics that must be integrated in the vicinity of the ion. The method presented can be readily applied to the investigation of charging effects beyond the context of ion trap experiments.Comment: 11 pages, 5 figure

Spatially-resolved potential measurement with ion crystals

We present a method to measure potentials over an extended region using one-dimensional ion crystals in a radio frequency (RF) ion trap. The equilibrium spacings of the ions within the crystal allow the determination of the external forces acting at each point. From this the overall potential, and also potentials due to specific trap features, are calculated. The method can be used to probe potentials near proximal objects in real time, and can be generalized to higher dimensions.Comment: 7 pages (double spaced), 3 figure

Demonstration of integrated microscale optics in surface-electrode ion traps

In ion trap quantum information processing, efficient fluorescence collection is critical for fast, high-fidelity qubit detection and ion-photon entanglement. The expected size of future many-ion processors require scalable light collection systems. We report on the development and testing of a microfabricated surface-electrode ion trap with an integrated high numerical aperture (NA) micromirror for fluorescence collection. When coupled to a low NA lens, the optical system is inherently scalable to large arrays of mirrors in a single device. We demonstrate stable trapping and transport of 40Ca+ ions over a 0.63 NA micromirror and observe a factor of 1.9 enhancement in photon collection compared to the planar region of the trap.Comment: 15 pages, 8 figure

Effects of air pollutant-temperature interactions on mineral-N dynamics and cation leaching in reciplicate forest soil transplantation experiments

Increased emissions of nitrogen compounds have led to atmospheric deposition to forest soils exceeding critical loads of N over large parts of Europe. To determine whether the chemistry of forest soils responds to changes in throughfall chemistry, intact soil columns were reciprocally transplanted between sites, with different physical conditions, across a gradient of N and S deposition in Europe. The transfer of a single soil to the various sites affected its net nitrification. This was not simply due to the nitrification of different levels of N deposition but was explained by differences in physical climates which influenced mineralization rates. Variation in the amount of net nitrification between soil types at a specific site were explained largely by soil pH. Within a site all soil types showed similar trends in net nitrification over time. Seasonal changes in net nitrification corresponds to oscillations in temperature but variable time lags had to be introduced to explain the relationships. With Arrhenius' law it was possible to approximate gross nitrification as a function of temperature. Gross nitrification equalled net nitrification after adaptation of the microbial community of transplanted soils to the new conditions. Time lags, and underestimates of gross nitrification in autumn, were assumed to be the result of increased NH4 + availability due either to changes in the relative rates of gross and net N transformations or to altered soil fauna-microbial interactions combined with improved moisture conditions. Losses of NO3/- were associated with Ca2+ and Mg2+ in non-acidified soil types and with losses of Al3+ in the acidified soils. For single soils the ion equilibrium equation of Gaines-Thomas provided a useful approximation of Al3+ concentrations in the soil solution as a function of the concentration of Ca2+. The between site deviations from this predicted equilibrium, which existed for single soils, could be explained by differences in throughfall chemistry which affected the total ionic strength of the soil solution. The approach of reciprocally transferring soil columns highlighted the importance of throughfall chemistry, interacting with the effect of changes in physical climate on forest soil acidification through internal proton production, in determining soil solution chemistry. A framework outlining the etiology of forest die-back induced by nitrogen saturation is proposed

Ionic balances of forest soils reciprocally transplanted among sites with varying pollution inputs.

Forest ecosystems are currently being exposed to changes in chemical inputs and it is suggested that physical climate is also changing. A novel approach has been used to study the effects of ionic inputs and climatic conditions on forest soils by reciprocally exchanging lysimeters containing undisturbed soil columns between four forest sites in Europe. The soil columns contained no living roots and simulated a clear cut situation. The soils chosen represented different stages of acidification and were taken from sites along a transect of increasing exposure to acidic and nitrogen pollution. The purpose of the study was to quantify the reactions of soils when transferred to different environments. Element balances were used as an aggregated indicator to describe the reaction of the soil. The input of protons in local throughfall increased along the transect from 0.01 kmol h

A bacterial process for selenium nanosphere assembly

During selenate respiration by Thauera selenatis, the reduction of selenate results in the formation of intracellular selenium (Se) deposits that are ultimately secreted as Se nanospheres of approximately 150 nm in diameter. We report that the Se nanospheres are associated with a protein of approximately 95 kDa. Subsequent experiments to investigate the expression and secretion profile of this protein have demonstrated that it is up-regulated and secreted in response to increasing selenite concentrations. The protein was purified from Se nanospheres, and peptide fragments from a tryptic digest were used to identify the gene in the draft T. selenatis genome. A matched open reading frame was located, encoding a protein with a calculated mass of 94.5 kDa. N-terminal sequence analysis of the mature protein revealed no cleavable signal peptide, suggesting that the protein is exported directly from the cytoplasm. The protein has been called Se factor A (SefA), and homologues of known function have not been reported previously. The sefA gene was cloned and expressed in Escherichia coli, and the recombinant His-tagged SefA purified. In vivo experiments demonstrate that SefA forms larger (approximately 300 nm) Se nanospheres in E. coli when treated with selenite, and these are retained within the cell. In vitro assays demonstrate that the formation of Se nanospheres upon the reduction of selenite by glutathione are stabilized by the presence of SefA. The role of SefA in selenium nanosphere assembly has potential for exploitation in bionanomaterial fabrication