94 research outputs found
Direct, Non-Destructive Imaging of Magnetization in a Spin-1 Bose Gas
Polarization-dependent phase-contrast imaging is used to spatially resolve
the magnetization of an optically trapped ultracold gas. This probe is applied
to Larmor precession of degenerate and nondegenerate spin-1 Rb gases.
Transverse magnetization of the Bose-Einstein condensate persists for the
condensate lifetime, with a spatial response to magnetic field inhomogeneities
consistent with a mean-field model of interactions. Rotational symmetry implies
that the Larmor frequency of a spinor condensate be density-independent, and
thus suitable for precise magnetometry with high spatial resolution. In
comparison, the magnetization of the noncondensed gas decoheres rapidly.Comment: 4 pages, 4 figure
Specular reflection of matter waves from a rough mirror
We have made a high resolution study of the specularity of the atomic reflection from an evanescent wave mirror using velocity selective Raman transitions. We have observed a double structure in the velocity distribution after reflection: a peak consistent with specular reflection and a diffuse reflection pedestal, whose contribution decreases rapidly with increasing detuning. The diffuse reflection is due to two distinct effects: spontaneous emission in the evanescent wave and a roughness in the evanescent wave potential whose amplitude is smaller than the de Broglie wavelength of the reflected atoms
Towards surface quantum optics with Bose-Einstein condensates in evanescent waves
We present a surface trap which allows for studying the coherent interaction
of ultracold atoms with evanescent waves. The trap combines a magnetic Joffe
trap with a repulsive evanescent dipole potential. The position of the magnetic
trap can be controlled with high precision which makes it possible to move
ultracold atoms to the surface of a glass prism in a controlled way. The
optical potential of the evanescent wave compensates for the strong attractive
van der Waals forces and generates a potential barrier at only a few hundred
nanometers from the surface. The trap is tested with Rb Bose-Einstein
condensates (BEC), which are stably positioned at distances from the surfaces
below one micrometer
Resolved diffraction patterns from a reflection grating for atoms
We have studied atomic diffraction at normal incidence from an evanescent
standing wave with a high resolution using velocity selective Raman
transitions. We have observed up to 3 resolved orders of diffraction, which are
well accounted for by a scalar diffraction theory. In our experiment the
transverse coherence length of the source is greater than the period of the
diffraction grating.Comment: 8 pages, 4 figure
Non-destructive, dynamic detectors for Bose-Einstein condensates
We propose and analyze a series of non-destructive, dynamic detectors for
Bose-Einstein condensates based on photo-detectors operating at the shot noise
limit. These detectors are compatible with real time feedback to the
condensate. The signal to noise ratio of different detection schemes are
compared subject to the constraint of minimal heating due to photon absorption
and spontaneous emission. This constraint leads to different optimal operating
points for interference-based schemes. We find the somewhat counter-intuitive
result that without the presence of a cavity, interferometry causes as much
destruction as absorption for optically thin clouds. For optically thick
clouds, cavity-free interferometry is superior to absorption, but it still
cannot be made arbitrarily non-destructive . We propose a cavity-based
measurement of atomic density which can in principle be made arbitrarily
non-destructive for a given signal to noise ratio
Dynamics of Dipolar Spinor Condensates
We study the semiclassical dynamics of a spinor condensate with the magnetic
dipole-dipole interaction included. The time evolution of the population
imbalance and the relative phase among different spin components depends
greatly on the relative strength of interactions as well as on the initial
conditions. The interplay of spin exchange and dipole-dipole interaction makes
it possible to manipulate the atomic population on different components,
leading to the phenomena of spontaneous magnetization and Macroscopic Quantum
Self Trapping. Simple estimate demonstrates that these effects are accessible
and controllable by modifying the geometry of the trapping potential.Comment: 13 pages,3 figure
Properties of Microelectromagnet Mirrors as Reflectors of Cold Rb Atoms
Cryogenically cooled microelectromagnet mirrors were used to reflect a cloud
of free-falling laser-cooled 85Rb atoms at normal incidence. The mirrors
consisted of microfabricated current-carrying Au wires in a periodic serpentine
pattern on a sapphire substrate. The fluorescence from the atomic cloud was
imaged after it had bounced off a mirror. The transverse width of the cloud
reached a local minimum at an optimal current corresponding to minimum mirror
roughness. A distinct increase in roughness was found for mirror configurations
with even versus odd number of lines. These observations confirm theoretical
predictions.Comment: Physical Review A, in print; 11 pages, 4 figure
Atazanavir and darunavir in pregnant women with HIV: Evaluation of laboratory and clinical outcomes from an observational national study
Background: Atazanavir and darunavir represent the main HIV PIs recommended in pregnancy, but comparativedata in pregnant women are limited.We assessed the safety and activity profile of these two drugs in pregnancyusing data from a national observational study.Methods: Women with atazanavir or darunavir exposure in pregnancy were evaluated for laboratory measuresand main pregnancy outcomes (e.g. preterm delivery, low birthweight, non-elective caesarean section and neonatalgestational age-adjusted birthweight Z-score).Results: Final analysis included 500 pregnancies with either atazanavir (n"409) or darunavir (n"91) exposure.No differences in pregnancy outcomes, weight gain in pregnancy, drug discontinuations, undetectable HIV-RNA,haemoglobin, ALT, total cholesterol, HDL cholesterol and LDL cholesterol were observed between the twogroups. At third trimester, exposure to darunavir was associated with higher levels of plasma triglycerides(median 235.5 versus 179 mg/dL; P"0.032) and a higher total cholesterol/HDL cholesterol ratio (median 4.03versus 3.27; P"0.028) and exposure to atazanavir was associated with higher levels of plasma bilirubin (1.54versus 0.32 mg/dL; P<0.001).Conclusions: In this observational study, the two main HIV PIs currently recommended by perinatal guidelinesshowed similar safety and activity in pregnancy, with no evidence of differences between the two drugs in termsof main pregnancy outcomes. Based on the minor differences observed in laboratory measures, prescribingphysicians might prefer either drug in some particular situations where the different impacts of treatment onlipid profile and bilirubin may have clinical relevance
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