570 research outputs found
Chronic pentamidine aerosol prophylaxis does not induce QT-prolongation and vetricular arrythmias
Association of ultracold double-species bosonic molecules
We report on the creation of heterospecies bosonic molecules, associated from
an ultracold Bose-Bose mixture of 41K and 87Rb, by using a resonantly modulated
magnetic field close to two Feshbach resonances. We measure the binding energy
of the weakly bound molecular states versus the Feshbach field and compare our
results to theoretical predictions. We observe the broadening and asymmetry of
the association spectrum due to thermal distribution of the atoms, and a
frequency shift occurring when the binding energy depends nonlinearly on the
Feshbach field. A simple model is developed to quantitatively describe the
association process. Our work marks an important step forward in the
experimental route towards Bose-Einstein condensates of dipolar molecules.Comment: 5 pages, 4 figure
High-order time-splitting Hermite and Fourier spectral methods
In this paper, we are concerned with the numerical solution of the time-dependent Gross-Pitaevskii Equation (GPE) involving a quasi-harmonic potential. Primarily, we consider discretisations that are based on spectral methods in space and higher-order exponential operator splitting methods in time. The resulting methods are favourable in view of accuracy and efficiency; moreover, geometric properties of the equation such as particle number and energy conservation are well captured. Regarding the spatial discretisation of the GPE, we consider two approaches. In the unbounded domain, we employ a spectral decomposition of the solution into Hermite basis functions: on the other hand. restricting the equation to a sufficiently large bounded domain, Fourier techniques are applicable. For the time integration of the GPE, we study various exponential operator splitting methods of convergence orders two, four, and six. Our main objective is to provide accuracy and efficiency comparisons of exponential operator splitting Fourier and Hermite pseudospectral methods for the time evolution of the GPE. Furthermore, we illustrate the effectiveness of higher-order time-splitting methods compared to standard integrators in a long-term integration
Collisional and molecular spectroscopy in an ultracold Bose-Bose mixture
The route toward a Bose-Einstein condensate of dipolar molecules requires the
ability to efficiently associate dimers of different chemical species and
transfer them to the stable rovibrational ground state. Here, we report on
recent spectroscopic measurements of two weakly bound molecular levels and
newly observed narrow d-wave Feshbach resonances. The data are used to improve
the collisional model for the Bose-Bose mixture 41K87Rb, among the most
promising candidates to create a molecular dipolar BEC.Comment: 13 pages, 3 figure
Observation of heteronuclear atomic Efimov resonances
The Efimov effect represents a cornerstone in few-body physics. Building on
the recent experimental observation with ultracold atoms, we report the first
experimental signature of Efimov physics in a heteronuclear system. A mixture
of K and Rb atoms was cooled to few hundred nanoKelvins and
stored in an optical dipole trap. Exploiting a broad interspecies Feshbach
resonance, the losses due to three-body collisions were studied as a function
of the interspecies scattering length. We observe an enhancement of the
three-body collisions for three distinct values of the interspecies scattering
lengths, both positive and negative. We attribute the two features at negative
scattering length to the existence of two kind of Efimov trimers, namely KKRb
and KRbRb.Comment: 4 pages, 4 figure
Acute Onset of Intermittent Claudication Caused by Complete Occlusion of a Persistent Sciatic Artery
High spatial resolution and temporally resolved t(2) (*) mapping of normal human myocardium at 7.0 tesla: an ultrahigh field magnetic resonance feasibility study
Myocardial tissue characterization using T(2) (*) relaxation mapping techniques is an emerging application of (pre)clinical cardiovascular magnetic resonance imaging. The increase in microscopic susceptibility at higher magnetic field strengths renders myocardial T(2) (*) mapping at ultrahigh magnetic fields conceptually appealing. This work demonstrates the feasibility of myocardial T(2) (*) imaging at 7.0 T and examines the applicability of temporally-resolved and high spatial resolution myocardial T(2) (*) mapping. In phantom experiments single cardiac phase and dynamic (CINE) gradient echo imaging techniques provided similar T(2) (*) maps. In vivo studies showed that the peak-to-peak B(0) difference following volume selective shimming was reduced to approximately 80 Hz for the four chamber view and mid-ventricular short axis view of the heart and to 65 Hz for the left ventricle. No severe susceptibility artifacts were detected in the septum and in the lateral wall for T(2) (*) weighting ranging from TE = 2.04 ms to TE = 10.2 ms. For TE >7 ms, a susceptibility weighting induced signal void was observed within the anterior and inferior myocardial segments. The longest T(2) (*) values were found for anterior (T(2) (*) = 14.0 ms), anteroseptal (T(2) (*) = 17.2 ms) and inferoseptal (T(2) (*) = 16.5 ms) myocardial segments. Shorter T(2) (*) values were observed for inferior (T(2) (*) = 10.6 ms) and inferolateral (T(2) (*) = 11.4 ms) segments. A significant difference (p = 0.002) in T(2) (*) values was observed between end-diastole and end-systole with T(2) (*) changes of up to approximately 27% over the cardiac cycle which were pronounced in the septum. To conclude, these results underscore the challenges of myocardial T(2) (*) mapping at 7.0 T but demonstrate that these issues can be offset by using tailored shimming techniques and dedicated acquisition schemes
Optomechanical deformation and strain in elastic dielectrics
Light forces induced by scattering and absorption in elastic dielectrics lead
to local density modulations and deformations. These perturbations in turn
modify light propagation in the medium and generate an intricate nonlinear
response. We generalise an analytic approach where light propagation in
one-dimensional media of inhomogeneous density is modelled as a result of
multiple scattering between polarizable slices. Using the Maxwell stress tensor
formalism we compute the local optical forces and iteratively approach
self-consistent density distributions where the elastic back-action balances
gradient- and scattering forces. For an optically trapped dielectric we derive
the nonlinear dependence of trap position, stiffness and total deformation on
the object's size and field configuration. Generally trapping is enhanced by
deformation, which exhibits a periodic change between stretching and
compression. This strongly deviates from qualitative expectations based on the
change of photon momentum of light crossing the surface of a dielectric. We
conclude that optical forces have to be treated as volumetric forces and that a
description using the change of photon momentum at the surface of a medium is
inappropriate
Ground state cooling, quantum state engineering and study of decoherence of ions in Paul traps
We investigate single ions of in Paul traps for quantum
information processing. Superpositions of the S electronic ground state
and the metastable D state are used to implement a qubit. Laser light
on the S D transition is used for the
manipulation of the ion's quantum state. We apply sideband cooling to the ion
and reach the ground state of vibration with up to 99.9% probability. Starting
from this Fock state , we demonstrate coherent quantum state
manipulation. A large number of Rabi oscillations and a ms-coherence time is
observed. Motional heating is measured to be as low as one vibrational quantum
in 190 ms. We also report on ground state cooling of two ions.Comment: 12 pages, 6 figures. submitted to Journal of Modern Optics, Special
Issue on Quantum Optics: Kuehtai 200
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