160 research outputs found
Momentum isotropisation in random potentials
When particles are multiply scattered by a random potential, their momentum
distribution becomes isotropic on average. We study this quantum dynamics
numerically and with a master equation. We show how to measure the elastic
scattering time as well as characteristic isotropisation times, which permit to
reconstruct the scattering phase function, even in rather strong disorder.Comment: 5 pages, paper contributed to Lyon BEC 2012; v2 minor changes,
version published in prin
Why are we failing to implement imaging studies with radiolabelled new molecular entities in early oncology drug development?
In early drug development advanced imaging techniques can help with progressing new molecular entities (NME) to subsequent phases of drug development and thus reduce attrition. However, several organizational, operational, and regulatory hurdles pose a significant barrier, potentially limiting the impact these techniques can have on modern drug development. Positron emission tomography (PET) of radiolabelled NME is arguably the best example of a complex technique with a potential to deliver unique decision-making data in small cohorts of subjects. However, to realise this potential the impediments to timely inclusion of PET into the drug development process must be overcome. In the present paper, we discuss the value of PET imaging with radiolabelled NME during early anticancer drug development, as exemplified with one such NME. We outline the multiple hurdles and propose options on how to streamline the organizational steps for future studies
Coherent Backscattering of Ultracold Atoms
We report on the direct observation of coherent backscattering (CBS) of
ultracold atoms, in a quasi-two-dimensional configuration. Launching atoms with
a well-defined momentum in a laser speckle disordered potential, we follow the
progressive build up of the momentum scattering pattern, consisting of a ring
associated with multiple elastic scattering, and the CBS peak in the backward
direction. Monitoring the depletion of the initial momentum component and the
formation of the angular ring profile allows us to determine microscopic
transport quantities. The time resolved evolution of the CBS peak is studied
and is found a fair agreement with predictions, at long times as well as at
short times. The observation of CBS can be considered a direct signature of
coherence in quantum transport of particles in disordered media. It is
responsible for the so called weak localization phenomenon, which is the
precursor of Anderson localization.Comment: 5 pages, 4 figure
Anisotropic 2D diffusive expansion of ultra-cold atoms in a disordered potential
We study the horizontal expansion of vertically confined ultra-cold atoms in
the presence of disorder. Vertical confinement allows us to realize a situation
with a few coupled harmonic oscillator quantum states. The disordered potential
is created by an optical speckle at an angle of 30{\deg} with respect to the
horizontal plane, resulting in an effective anisotropy of the correlation
lengths of a factor of 2 in that plane. We observe diffusion leading to
non-Gaussian density profiles. Diffusion coefficients, extracted from the
experimental results, show anisotropy and strong energy dependence, in
agreement with numerical calculations
Synthesis of carbon-11 radiolabelled transition metal complexes using 11C-dithiocarbamates
A novel radiolabelling method exploiting 11C-dithiocarbamate ligands has been used to generate 11C-labelled Au(I), Au(III), Pd(II) and Pt(II) complexes in high radiochemical yields (71–99%). Labelled complexes were prepared in a rapid one-pot procedure via the substitution reaction of 11C-dithiocarbamate ligands with appropriate transition metal chloride precursors
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
Coherence properties of a 2D trapped Bose gas around the superfluid transition
We measure the momentum distribution of a 2D trapped Bose gas and observe the
increase of the range of coherence around the Berezinskii-Kosterlitz-Thouless
(BKT) transition. We quantitatively compare our observed profiles to both a
Hartee-Fock mean-field theory and to quantum Monte-Carlo simulations. In the
normal phase, we already observe a sharpening of the momentum distribution.
This behavior is partially captured in a mean-field approach, in contrast to
the physics of the BKT transition
Theoretical Analysis of a Large Momentum Beamsplitter using Bloch Oscillations
In this paper, we present the implementation of Bloch oscillations in an
atomic interferometer to increase the separation of the two interfering paths.
A numerical model, in very good agreement with the experiment, is developed.
The contrast of the interferometer and its sensitivity to phase fluctuations
and to intensity fluctuations are also calculated. We demonstrate that the
sensitivity to phase fluctuations can be significantly reduced by using a
suitable arrangement of Bloch oscillations pulses
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