731 research outputs found
Spin-Injection Spectroscopy of a Spin-Orbit Coupled Fermi Gas
The coupling of the spin of electrons to their motional state lies at the
heart of recently discovered topological phases of matter. Here we create and
detect spin-orbit coupling in an atomic Fermi gas, a highly controllable form
of quantum degenerate matter. We reveal the spin-orbit gap via spin-injection
spectroscopy, which characterizes the energy-momentum dispersion and spin
composition of the quantum states. For energies within the spin-orbit gap, the
system acts as a spin diode. To fully inhibit transport, we open an additional
spin gap, thereby creating a spin-orbit coupled lattice whose spinful band
structure we probe. In the presence of s-wave interactions, such systems should
display induced p-wave pairing, topological superfluidity, and Majorana edge
states
NileTMRG at SemEval-2017 Task 4: Arabic Sentiment Analysis
This paper describes two systems that were used by the authors for addressing
Arabic Sentiment Analysis as part of SemEval-2017, task 4. The authors
participated in three Arabic related subtasks which are: Subtask A (Message
Polarity Classification), Sub-task B (Topic-Based Message Polarity
classification) and Subtask D (Tweet quantification) using the team name of
NileTMRG. For subtask A, we made use of our previously developed sentiment
analyzer which we augmented with a scored lexicon. For subtasks B and D, we
used an ensemble of three different classifiers. The first classifier was a
convolutional neural network for which we trained (word2vec) word embeddings.
The second classifier consisted of a MultiLayer Perceptron, while the third
classifier was a Logistic regression model that takes the same input as the
second classifier. Voting between the three classifiers was used to determine
the final outcome. The output from task B, was quantified to produce the
results for task D. In all three Arabic related tasks in which NileTMRG
participated, the team ranked at number one
Cryogenic Ion Trapping Systems with Surface-Electrode Traps
We present two simple cryogenic RF ion trap systems in which cryogenic
temperatures and ultra high vacuum pressures can be reached in as little as 12
hours. The ion traps are operated either in a liquid helium bath cryostat or in
a low vibration closed cycle cryostat. The fast turn around time and
availability of buffer gas cooling made the systems ideal for testing
surface-electrode ion traps. The vibration amplitude of the closed cycled
cryostat was found to be below 106 nm. We evaluated the systems by loading
surface-electrode ion traps with Sr ions using laser ablation, which
is compatible with the cryogenic environment. Using Doppler cooling we observed
small ion crystals in which optically resolved ions have a trapped lifetime
over 2500 minutes.Comment: 10 pages, 13 EPS figure
Laser ablation loading of a surface-electrode ion trap
We demonstrate loading by laser ablation of Sr ions into a
mm-scale surface-electrode ion trap. The laser used for ablation is a pulsed,
frequency-tripled Nd:YAG with pulse energies of 1-10 mJ and durations of 3-5
ns. An additional laser is not required to photoionize the ablated material.
The efficiency and lifetime of several candidate materials for the laser
ablation target are characterized by measuring the trapped ion fluorescence
signal for a number of consecutive loads. Additionally, laser ablation is used
to load traps with a trap depth (40 meV) below where electron impact ionization
loading is typically successful ( 500 meV).Comment: 4 pages, 4 figure
Data of chemical analysis and electrical properties of SnO2-TiO2 composite nanofibers
In this data article, we provide energy dispersive X-ray spectroscopy (EDX) spectra of the electrospun composite (SnO2-TiO2) nanowires with the elemental values measured in atomic and weight%. The linear sweep voltammetry data of composite and its component nanofibers are provided. The data collected in this article is directly related to our research article “Synergistic combination of electronic and electrical properties of SnO2 and TiO2 in a single SnO2-TiO2 composite nanowire for dye-sensitized solar cells
Experimental investigation of planar ion traps
Chiaverini et al. [Quant. Inf. Comput. 5, 419 (2005)] recently suggested a
linear Paul trap geometry for ion trap quantum computation that places all of
the electrodes in a plane. Such planar ion traps are compatible with modern
semiconductor fabrication techniques and can be scaled to make compact, many
zone traps. In this paper we present an experimental realization of planar ion
traps using electrodes on a printed circuit board to trap linear chains of tens
of 0.44 micron diameter charged particles in a vacuum of 15 Pa (0.1 torr). With
these traps we address concerns about the low trap depth of planar ion traps
and develop control electrode layouts for moving ions between trap zones
without facing some of the technical difficulties involved in an atomic ion
trap experiment. Specifically, we use a trap with 36 zones (77 electrodes)
arranged in a cross to demonstrate loading from a traditional four rod linear
Paul trap, linear ion movement, splitting and joining of ion chains, and
movement of ions through intersections. We further propose an additional DC
biased electrode above the trap which increases the trap depth dramatically,
and a novel planar ion trap geometry that generates a two dimensional lattice
of point Paul traps.Comment: 11 pages, 20 figure
5-(4-FluoroÂphenÂyl)-3-[5-methyl-1-(4-methylÂphenÂyl)-1H-1,2,3-triazol-4-yl]-4,5-dihydro-1H-pyrazole-1-carbothioÂamide
In the title compound, C20H19FN6S, the pyrazole ring has an envelope conformation, with the methine C atom being the flap atom. The dihedral angle between the least-squares plane through the pyrazole and triazole rings is 7.59 (9)°, and the triazole and attached benzene ring form a dihedral angle of 74.79 (9)°. The thioÂurea group is coplanar with the pyrazole ring [N—N—C—S torsion angle = −179.93 (11)°], which enables the formation of an intraÂmolecular N—H⋯N hydrogen bond. In the crystal, inversion-related molÂecules associate via N—H⋯S hydrogen bonds and eight-membered {⋯HNCS}2 synthons feature in the crystal packing. These synthons are connected into supraÂmolecular chains along the a axis via N—H⋯F hydrogen bonds, and the chains are consolidated into layers in the ab plane via C—H⋯S and C—H⋯F contacts
4-{1-[4-(4-BromoÂphenÂyl)-1,3-thiaÂzol-2-yl]-5-(4-fluoroÂphenÂyl)-4,5-dihydro-1H-pyrazol-3-yl}-5-methyl-1-(4-methylÂphenÂyl)-1H-1,2,3-triazole
In the title compound, C28H22BrFN6S, the central pyrazole ring has an envelope conformation, with the methine C atom being the flap atom. The dihedral angles between the least-squares plane through this ring and the adjacent thiaÂzole [18.81 (15)°] and triazole [1.83 (16)°] rings indicate a twist in the molÂecule. A further twist is evident by the dihedral angle of 64.48 (16)° between the triazole ring and the attached benzene ring. In the crystal, C—H⋯N, C—H⋯F, C—H⋯π and π–π interÂactions [occurring between the thiaÂzole and triazole rings, centroid–centroid distance = 3.571 (2) Å] link molÂecules into a three-dimensional architecture. The sample studied was a non-merohedral twin; the minor twin component refined to 47.16 (7)%
Lattice dynamical signature of charge density wave formation in underdoped YBa2Cu3O6+x
We report a detailed Raman scattering study of the lattice dynamics in
detwinned single crystals of the underdoped high temperature superconductor
YBa2Cu3O6+x (x=0.75, 0.6, 0.55 and 0.45). Whereas at room temperature the
phonon spectra of these compounds are similar to that of optimally doped
YBa2Cu3O6.99, additional Raman-active modes appear upon cooling below ~170-200
K in underdoped crystals. The temperature dependence of these new features
indicates that they are associated with the incommensurate charge density wave
state recently discovered using synchrotron x-ray scattering techniques on the
same single crystals. Raman scattering has thus the potential to explore the
evolution of this state under extreme conditions.Comment: 12 pages, 11 figure
Single-particle-sensitive imaging of freely propagating ultracold atoms
We present a novel imaging system for ultracold quantum gases in expansion.
After release from a confining potential, atoms fall through a sheet of
resonant excitation laser light and the emitted fluorescence photons are imaged
onto an amplified CCD camera using a high numerical aperture optical system.
The imaging system reaches an extraordinary dynamic range, not attainable with
conventional absorption imaging. We demonstrate single-atom detection for
dilute atomic clouds with high efficiency where at the same time dense
Bose-Einstein condensates can be imaged without saturation or distortion. The
spatial resolution can reach the sampling limit as given by the 8 \mu m pixel
size in object space. Pulsed operation of the detector allows for slice images,
a first step toward a 3D tomography of the measured object. The scheme can
easily be implemented for any atomic species and all optical components are
situated outside the vacuum system. As a first application we perform
thermometry on rubidium Bose-Einstein condensates created on an atom chip.Comment: 24 pages, 10 figures. v2: as publishe
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