66 research outputs found
Suppression of Dephasing of Optically Trapped Atoms
Ultra-cold atoms trapped in an optical dipole trap and prepared in a coherent
superposition of their hyperfine ground states, decohere as they interact with
their environment. We demonstrate than the loss in coherence in an "echo"
experiment, which is caused by mechanisms such as Rayleigh scattering, can be
suppressed by the use of a new pulse sequence. We also show that the coherence
time is then limited by mixing to other vibrational levels in the trap and by
the finite lifetime of the internal quantum states of the atoms
Echo spectroscopy and Atom Optics Billiards
We discuss a recently demonstrated type of microwave spectroscopy of trapped
ultra-cold atoms known as "echo spectroscopy" [M.F. Andersen et. al., Phys.
Rev. Lett., in press (2002)]. Echo spectroscopy can serve as an extremely
sensitive experimental tool for investigating quantum dynamics of trapped atoms
even when a large number of states are thermally populated. We show numerical
results for the stability of eigenstates of an atom-optics billiard of the
Bunimovich type, and discuss its behavior under different types of
perturbations. Finally, we propose to use special geometrical constructions to
make a dephasing free dipole trap
Interaction of hot spots and THz waves in Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks of various geometry
At high enough input power in stacks of Bi_2Sr_2CaCu_2O8 intrinsic Josephson
junctions a hot spot (a region heated to above the superconducting transition
temperature) coexists with regions still in the superconducting state. In the
``cold'' regions cavity resonances can occur, synchronizing the ac Josephson
currents and giving rise to strong coherent THz emission. We investigate the
interplay of hot spots and standing electromagnetic waves by low temperature
scanning laser microscopy and THz emission measurements, using stacks of
various geometries. For a rectangular and a arrow-shaped structure we show that
the standing wave can be turned on and off in various regions of the stack
structure, depending on the hot spot position. We also report on standing wave
and hot spot formation in a disk shaped mesa structure
Hyperfine Spectroscopy of Optically Trapped Atoms
We perform spectroscopy on the hyperfine splitting of Rb atoms trapped
in far-off-resonance optical traps. The existence of a spatially dependent
shift in the energy levels is shown to induce an inherent dephasing effect,
which causes a broadening of the spectroscopic line and hence an inhomogeneous
loss of atomic coherence at a much faster rate than the homogeneous one caused
by spontaneous photon scattering. We present here a number of approaches for
reducing this inhomogeneous broadening, based on trap geometry, additional
laser fields, and novel microwave pulse sequences. We then show how hyperfine
spectroscopy can be used to study quantum dynamics of optically trapped atoms.Comment: Review/Tutoria
Single-Spin Addressing in an Atomic Mott Insulator
Ultracold atoms in optical lattices are a versatile tool to investigate
fundamental properties of quantum many body systems. In particular, the high
degree of control of experimental parameters has allowed the study of many
interesting phenomena such as quantum phase transitions and quantum spin
dynamics. Here we demonstrate how such control can be extended down to the most
fundamental level of a single spin at a specific site of an optical lattice.
Using a tightly focussed laser beam together with a microwave field, we were
able to flip the spin of individual atoms in a Mott insulator with
sub-diffraction-limited resolution, well below the lattice spacing. The Mott
insulator provided us with a large two-dimensional array of perfectly arranged
atoms, in which we created arbitrary spin patterns by sequentially addressing
selected lattice sites after freezing out the atom distribution. We directly
monitored the tunnelling quantum dynamics of single atoms in the lattice
prepared along a single line and observed that our addressing scheme leaves the
atoms in the motional ground state. Our results open the path to a wide range
of novel applications from quantum dynamics of spin impurities, entropy
transport, implementation of novel cooling schemes, and engineering of quantum
many-body phases to quantum information processing.Comment: 8 pages, 5 figure
The handbook for standardised field and laboratory measurements in terrestrial climate-change experiments and observational studies
Climate change is a worldwide threat to biodiversity and ecosystem structure, functioning, and services. To understand the underlying drivers and mechanisms, and to predict the consequences for nature and people, we urgently need better understanding of the direction and magnitude of climateâchange impacts across the soilâplantâatmosphere continuum. An increasing number of climateâchange studies is creating new opportunities for meaningful and highâquality generalisations and improved process understanding. However, significant challenges exist related to data availability and/or compatibility across studies, compromising opportunities for data reâuse, synthesis, and upscaling. Many of these challenges relate to a lack of an established âbest practiceâ for measuring key impacts and responses. This restrains our current understanding of complex processes and mechanisms in terrestrial ecosystems related to climate change
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Non-structural carbohydrates in woody plants compared among laboratories
Non-structural carbohydrates (NSC) in plant tissue are frequently quantified to make inferences about plant responses to environmental conditions. Laboratories publishing estimates of NSC of woody plants use many different methods to evaluate NSC. We asked whether NSC estimates in the recent literature could be quantitatively compared among studies. We also asked whether any differences among laboratories were related to the extraction and quantification methods used to determine starch and sugar concentrations. These questions were addressed by sending sub-samples collected from five woody plant tissues, which varied in NSC content and chemical composition, to 29 laboratories. Each laboratory analyzed the samples with their laboratory-specific protocols, based on recent publications, to determine concentrations of soluble sugars, starch and their sum, total NSC. Laboratory estimates differed substantially for all samples. For example, estimates for Eucalyptus globulus leaves (EGL) varied from 23 to 116 (mean = 56) mg gâ»Âč for soluble sugars, 6â533 (mean = 94) mg gâ»Âč for starch and 53â649 (mean = 153) mg gâ»Âč for total NSC. Mixed model analysis of variance showed that much of the variability among laboratories was unrelated to the categories we used for extraction and quantification methods (method category RÂČ = 0.05â0.12 for soluble sugars, 0.10â0.33 for starch and 0.01â0.09 for total NSC). For EGL, the difference between the highest and lowest least squares means for categories in the mixed model analysis was 33 mg gâ»Âč for total NSC, compared with the range of laboratory estimates of 596 mg gâ»Âč. Laboratories were reasonably consistent in their ranks of estimates among tissues for starch (r = 0.41â0.91), but less so for total NSC (r = 0.45â0.84) and soluble sugars (r = 0.11â0.83). Our results show that NSC estimates for woody plant tissues cannot be compared among laboratories. The relative changes in NSC between treatments measured within a laboratory may be comparable within and between laboratories, especially for starch. To obtain comparable NSC estimates, we suggest that users can either adopt the reference method given in this publication, or report estimates for a portion of samples using the reference method, and report estimates for a standard reference material. Researchers interested in NSC estimates should work to identify and adopt standard methods.This is the publisherâs final pdf. The published article is copyrighted by the author(s) and published by Oxford University Press. The published article can be found at: http://treephys.oxfordjournals.org/Keywords: soluble sugars, starch, particle size, reference method, standardization, non-structural carbohydrate chemical analysis, extraction and quantification consistenc
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