329 research outputs found
The Role of Source Coherence in Atom Interferometery
The role of source cloud spatial coherence in a Mach-Zehnder type atom
interferometer is experimentally investigated. The visibility and contrast of a
Bose-Einstein condensate (BEC) and three thermal sources with varying spatial
coherence are compared as a function of interferometer time. At short times,
the fringe visibility of a BEC source approaches 100 % nearly independent of pi
pulse efficiency, while thermal sources have fringe visibilities limited to the
mirror efficiency. More importantly for precision measurement systems, the BEC
source maintains interference at interferometer times significantly beyond the
thermal source
80hk Momentum Separation with Bloch Oscillations in an Optically Guided Atom Interferometer
We demonstrate phase sensitivity in a horizontally guided,
acceleration-sensitive atom interferometer with a momentum separation of 80hk
between its arms. A fringe visibility of 7% is observed. Our coherent pulse
sequence accelerates the cold cloud in an optical waveguide, an inherently
scalable route to large momentum separation and high sensitivity. We maintain
coherence at high momentum separation due to both the transverse confinement
provided by the guide, and our use of optical delta-kick cooling on our
cold-atom cloud. We also construct a horizontal interferometric gradiometer to
measure the longitudinal curvature of our optical waveguide.Comment: 6 pages, 6 figure
A Bright Solitonic Matter-Wave Interferometer
We present the first realisation of a solitonic atom interferometer. A
Bose-Einstein condensate of atoms of rubidium-85 is loaded into a
horizontal optical waveguide. Through the use of a Feshbach resonance, the
-wave scattering length of the Rb atoms is tuned to a small negative
value. This attractive atomic interaction then balances the inherent
matter-wave dispersion, creating a bright solitonic matter wave. A Mach-Zehnder
interferometer is constructed by driving Bragg transitions with the use of an
optical lattice co-linear with the waveguide. Matter wave propagation and
interferometric fringe visibility are compared across a range of -wave
scattering values including repulsive, attractive and non-interacting values.
The solitonic matter wave is found to significantly increase fringe visibility
even compared with a non-interacting cloud.Comment: 6 pages, 4 figure
Non-destructive shadowgraph imaging of ultracold atoms
An imaging system is presented that is capable of far-detuned non-destructive
imaging of a Bose-Einstein condensate with the signal proportional to the
second spatial derivative of the density. Whilst demonstrated with application
to , the technique generalizes to other atomic species and is
shown to be capable of a signal to noise of at GHz detuning with
in-trap images showing no observable heating or atom loss. The technique
is also applied to the observation of individual trajectories of stochastic
dynamics inaccessible to single shot imaging. Coupled with a fast optical phase
lock loop, the system is capable of dynamically switching to resonant
absorption imaging during the experiment.Comment: 4 pages, 5 figure
A quantum sensor: simultaneous precision gravimetry and magnetic gradiometry with a Bose-Einstein condensate
A Bose-Einstein condensate is used as an atomic source for a high precision
sensor. A atom F=1 spinor condensate of Rb is released
into free fall for up to ms and probed with a Mach-Zehnder atom
interferometer based on Bragg transitions. The Bragg interferometer
simultaneously addresses the three magnetic states, , facilitating a simultaneous measurement of the acceleration due
to gravity with an asymptotic precision of g/g and
the magnetic field gradient to a precision pT/m
Prediction of peptide and protein propensity for amyloid formation
Understanding which peptides and proteins have the potential to undergo amyloid formation and what driving forces are responsible for amyloid-like fiber formation and stabilization remains limited. This is mainly because proteins that can undergo structural changes, which lead to amyloid formation, are quite diverse and share no obvious sequence or structural homology, despite the structural similarity found in the fibrils. To address these issues, a novel approach based on recursive feature selection and feed-forward neural networks was undertaken to identify key features highly correlated with the self-assembly problem. This approach allowed the identification of seven physicochemical and biochemical properties of the amino acids highly associated with the self-assembly of peptides and proteins into amyloid-like fibrils (normalized frequency of β-sheet, normalized frequency of β-sheet from LG, weights for β-sheet at the window position of 1, isoelectric point, atom-based hydrophobic moment, helix termination parameter at position j+1 and ΔGº values for peptides extrapolated in 0 M urea). Moreover, these features enabled the development of a new predictor (available at http://cran.r-project.org/web/packages/appnn/index.html) capable of accurately and reliably predicting the amyloidogenic propensity from the polypeptide sequence alone with a prediction accuracy of 84.9 % against an external validation dataset of sequences with experimental in vitro, evidence of amyloid formation
Exclusive Photoproduction of the Cascade (Xi) Hyperons
We report on the first measurement of exclusive Xi-(1321) hyperon
photoproduction in gamma p --> K+ K+ Xi- for 3.2 < E(gamma) < 3.9 GeV. The
final state is identified by the missing mass in p(gamma,K+ K+)X measured with
the CLAS detector at Jefferson Laboratory. We have detected a significant
number of the ground-state Xi-(1321)1/2+, and have estimated the total cross
section for its production. We have also observed the first excited state
Xi-(1530)3/2+. Photoproduction provides a copious source of Xi's. We discuss
the possibilities of a search for the recently proposed Xi5-- and Xi5+
pentaquarks.Comment: submitted to Phys. Rev.
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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