969 research outputs found
Using adiabatic coupling techniques in atom-chip waveguide structures
Adiabatic techniques are well known tools in multi-level electron systems to
transfer population between different states with high fidelity. Recently it
has been realised that these ideas can also be used in ultra-cold atom systems
to achieve coherent manipulation of the atomic centre-of-mass states. Here we
present an investigation into a realistic setup using three atomic waveguides
created on top of an atom chip and show that such systems hold large potential
for the observation of adiabatic phenomena in experiments.Comment: 10 pages, 6 figures, accepted for publication in Physica Scripta for
the CEWQO2009 proceeding
Deterministic single-atom excitation via adiabatic passage and Rydberg blockade
We propose to use adiabatic rapid passage with a chirped laser pulse in the
strong dipole blockade regime to deterministically excite only one Rydberg atom
from randomly loaded optical dipole traps or optical lattices. The chirped
laser excitation is shown to be insensitive to the random number \textit{N} of
the atoms in the traps. Our method overcomes the problem of the
dependence of the collective Rabi frequency, which was the main obstacle for
deterministic single-atom excitation in the ensembles with unknown \textit{N},
and can be applied for single-atom loading of dipole traps and optical
lattices.Comment: 6 pages, 5 figures. Version 5 is expanded and submitted to PRA. Typo
in Fig.4 corrected in Version 2. Version 3 and 4 are duplicates of V
Sublattice addressing and spin-dependent motion of atoms in a double-well lattice
We load atoms into every site of an optical lattice and selectively spin flip
atoms in a sublattice consisting of every other site. These selected atoms are
separated from their unselected neighbors by less than an optical wavelength.
We also show spin-dependent transport, where atomic wave packets are coherently
separated into adjacent sites according to their internal state. These tools
should be useful for quantum information processing and quantum simulation of
lattice models with neutral atoms
Profiteers of environmental change in the Swiss Alps: increase of thermophilous and generalist plants in wetland ecosystems within the last 10years
It has been predicted that Europe will experience a rise in temperature of 2.2-5.3°C within this century. This increase in temperature may lead to vegetation change along altitudinal gradients. To test whether vegetation composition has already changed in the recent decade due to current warming (and other concomitant environmental changes), we recorded plant species composition in 1995 and 2005/2006 in Swiss pre-alpine fen meadows (800-1,400ma.s.l.). Despite no obvious changes in the management of these fens, overall, plant species richness (cumulative number of plant species at five plots per site) significantly increased over this period. This was mainly due to an increase in the number of thermophilous, rich-soil-indicator and shade-indicator species, which corresponded to increased community productivity and shading within the vegetation layer. In contrast, fen specialists significantly declined in species numbers. The strongest species shifts occurred at the lowest sites, which overall had a higher colonization rate by new species than did sites at higher altitudes. Vegetation change along the altitudinal gradient was also affected by different types of land management: early-flowering species and species with low habitat specificity had high colonization rates in grazed fens, especially at low altitude
Extracting Accurate Long-Term Behavior Changes from a Large Pig Dataset
Visual observation of uncontrolled real-world behavior leads to noisy observations, complicated by occlusions, ambiguity, variable motion rates, detection and tracking errors, slow transitions between behaviors, etc. We show in this paper that reliable estimates of long-term trends can be extracted given enough data, even though estimates from individual frames may be noisy. We validate this concept using a new public dataset of approximately 20+ million daytime pig observations over 6 weeks of their main growth stage, and we provide annotations for various tasks including 5 individual behaviors. Our pipeline chains detection, tracking and behavior classification combining deep and shallow computer vision techniques. While individual detections may be noisy, we show that long-term behavior changes can still be extracted reliably, and we validate these results qualitatively on the full dataset. Eventually, starting from raw RGB video data we are able to both tell what pigs main daily activities are, and how these change through time
Bose-Einstein condensation in dark power-law laser traps
We investigate theoretically an original route to achieve Bose-Einstein
condensation using dark power-law laser traps. We propose to create such traps
with two crossing blue-detuned Laguerre-Gaussian optical beams. Controlling
their azimuthal order allows for the exploration of a multitude of
power-law trapping situations in one, two and three dimensions, ranging from
the usual harmonic trap to an almost square-well potential, in which a
quasi-homogeneous Bose gas can be formed. The usual cigar-shaped and
disk-shaped Bose-Einstein condensates obtained in a 1D or 2D harmonic trap take
the generic form of a "finger" or of a "hockey puck" in such Laguerre-Gaussian
traps. In addition, for a fixed atom number, higher transition temperatures are
obtained in such configurations when compared with a harmonic trap of same
volume. This effect, which results in a substantial acceleration of the
condensation dynamics, requires a better but still reasonable focusing of the
Laguerre-Gaussian beams
Measurement of the electric dipole moments for transitions to rubidium Rydberg states via Autler-Townes splitting
We present the direct measurements of electric-dipole moments for
transitions with for Rubidium atoms. The
measurements were performed in an ultracold sample via observation of the
Autler-Townes splitting in a three-level ladder scheme, commonly used for
2-photon excitation of Rydberg states. To the best of our knowledge, this is
the first systematic measurement of the electric dipole moments for transitions
from low excited states of rubidium to Rydberg states. Due to its simplicity
and versatility, this method can be easily extended to other transitions and
other atomic species with little constraints. Good agreement of the
experimental results with theory proves the reliability of the measurement
method.Comment: 12 pages, 6 figures; figure 6 replaced with correct versio
Bending the curve: Simple but massive conservation action leads to landscape-scale recovery of amphibians
Success stories are rare in conservation science, hindered also by the research-implementation gap, where scientific insights rarely inform practice and practical implementation is rarely evaluated scientifically. Amphibian population declines, driven by multiple stressors, are emblematic of the freshwater biodiversity crisis. Habitat creation is a straightforward conservation action that has been shown to locally benefit amphibians, as well as other taxa, but does it benefit entire amphibian communities at large spatial scales? Here, we evaluate a landscape-scale pond-construction program by fitting dynamic occupancy models to 20 y of monitoring data for 12 pond-breeding amphibian species in the Swiss state Aargau, a densely populated area of the Swiss lowlands with intensive land use. After decades of population declines, the number of occupied ponds increased statewide for 10 out of 12 species, while one species remained stable and one species further declined between 1999 and 2019. Despite regional differences, in 77% of all 43 regional metapopulations, the colonization and subsequent occupation of new ponds stabilized (14%) or increased (63%) metapopulation size. Likely mechanisms include increased habitat availability, restoration of habitat dynamics, and increased connectivity between ponds. Colonization probabilities reflected species-specific preferences for characteristics of ponds and their surroundings, which provides evidence-based information for future pond construction targeting specific species. The relatively simple but landscape-scale and persistent conservation action of constructing hundreds of new ponds halted declines and stabilized or increased the state-wide population size of all but one species, despite ongoing pressures from other stressors in a human-dominated landscape
Vacuum Solutions of Einstein's Equations in Parabolic Coordinates
We present a simple method to obtain vacuum solutions of Einstein's equations
in parabolic coordinates starting from ones with cylindrical symmetries.
Furthermore, a generalization of the method to a more general situation is
given together with a discussion of the possible relations between our method
and the Belinsky-Zakharov soliton-generating solutions.Comment: 15 pages, version published in Class. Quantum Gra
- …