754 research outputs found
Single ions trapped in a one-dimensional optical lattice
We report on three-dimensional optical trapping of single ions in an optical
lattice formed by two counter-propagating laser beams. We characterize the
trapping parameters of the standing wave using the ion as a sensor stored in a
hybrid trap consisting of a radio-frequency (rf), a dc, and the optical
potential. When loading ions directly from the rf into the standing-wave trap,
we observe a dominant heating rate. Monte Carlo simulations confirm rf-induced
parametric excitations within the deep optical lattice as the main source. We
demonstrate a way around this effect by an alternative transfer protocol which
involves an intermediate step of optical confinement in a single-beam trap
avoiding the temporal overlap of the standing wave and the rf field.
Implications arise for hybrid (rf/optical) and pure optical traps as platforms
for ultra-cold chemistry experiments exploring atom--ion collisions or quantum
simulation experiments with ions, or combinations of ions and atoms.Comment: 5 pages, 4 figure
Two-loop current-current operator contribution to the non-leptonic QCD penguin amplitude
The computation of direct CP asymmetries in charmless B decays at
next-to-next-to-leading order (NNLO) in QCD is of interest to ascertain the
short-distance contribution. Here we compute the two-loop penguin contractions
of the current-current operators Q_{1,2} and provide a first estimate of NNLO
CP asymmetries in penguin-dominated b -> s transitions.Comment: 14 pages, 4 figures, 1 tabl
A puzzle in decays and extraction of the fragmentation fraction
We provide updated predictions for the hadronic decays and . They are based on
results for the QCD factorization amplitudes at
leading power and on recent results for the
form factors up to order in the
heavy-quark expansion. We give quantitative estimates of the matrix elements
entering the hadronic decay amplitudes at order for the first time. Our results are very precise, and uncover a
substantial discrepancy between the theory predictions and the experimental
measurements. We explore two possibilities for this discrepancy:
non-factorizable contributions larger than predicted by the QCD factorization
power counting, and contributions beyond the Standard Model. We determine the
fragmentation fraction for the CDF, D0 and LHCb experiments for both
scenarios.Comment: 13 pages, 4 tables: v2: minor modifications, accepted for publication
in EPJ
Influence of static electric fields on an optical ion trap
We recently reported on a proof-of-principle experiment demonstrating optical
trapping of an ion in a single-beam dipole trap superimposed by a static
electric potential [Nat. Photonics 4, 772--775 (2010)]. Here, we first discuss
the experimental procedures focussing on the influence and consequences of the
static electric potential. These potentials can easily prevent successful
optical trapping, if their configuration is not chosen carefully. Afterwards,
we analyse the dipole trap experiments with different analytic models, in which
different approximations are applied. According to these models the
experimental results agree with recoil heating as the relevant heating effect.
In addition, a Monte-Carlo simulation has been developed to refine the
analysis. It reveals a large impact of the static electric potential on the
dipole trap experiments in general. While it supports the results of the
analytic models for the parameters used in the experiments, the analytic models
cease their validity for significantly different parameters. Finally, we
propose technical improvements for future realizations of experiments with
optically trapped ions.Comment: 16 pages, 16 figure
Technological implementation of a photonic Bier-Glass cavity
In this paper, we introduce a novel quantum photonic device, which we term
photonic Bier-Glass cavity. We discuss its fabrication and functionality, which
is based on the coupling of integrated In(Ga)As quantum dots to a broadband
photonic cavity resonance. By design, the device architecture uniquely combines
the Purcell enhancement of a photonic micropillar structure with broadband
photonic mode shaping of a vertical, tapered waveguide, making it an
interesting candidate to enable the efficient extraction of entangled photon
pairs. We detail the epitaxial growth of the heterostructure and the necessary
lithography steps to approach a GaAs-based photonic device with a height
exceeding 15 m, supported on a pedestal that can be as thin as 20 nm. We
present an optical characterization, which confirms the presence of broadband
optical resonances, in conjunction with amplified spontaneous emission of
single photons.Comment: 14 pages, 9 figure
Nonlinear terahertz control of the lead halide perovskite lattice
Lead halide perovskites (LHPs) have emerged as an excellent class of semiconductors for next-generation solar cells and optoelectronic devices. Tailoring physical properties by fine-tuning the lattice structures has been explored in these materials by chemical composition or morphology. Nevertheless, its dynamic counterpart, phonon-driven ultrafast material control, as contemporarily harnessed for oxide perovskites, has not yet been established. Here, we use intense THz electric fields to obtain direct lattice control via nonlinear excitation of coherent octahedral twist modes in hybrid CH3NH3PbBr3 and all-inorganic CsPbBr3 perovskites. These Raman-active phonons at 0.9 to 1.3 THz are found to govern the ultrafast THz-induced Kerr effect in the low-temperature orthorhombic phase and thus dominate the phonon-modulated polarizability with potential implications for dynamic charge carrier screening beyond the Fröhlich polaron. Our work opens the door to selective control of LHP’s vibrational degrees of freedom governing phase transitions and dynamic disorder
Stimulus - response curves of a neuronal model for noisy subthreshold oscillations and related spike generation
We investigate the stimulus-dependent tuning properties of a noisy ionic
conductance model for intrinsic subthreshold oscillations in membrane potential
and associated spike generation. On depolarization by an applied current, the
model exhibits subthreshold oscillatory activity with occasional spike
generation when oscillations reach the spike threshold. We consider how the
amount of applied current, the noise intensity, variation of maximum
conductance values and scaling to different temperature ranges alter the
responses of the model with respect to voltage traces, interspike intervals and
their statistics and the mean spike frequency curves. We demonstrate that
subthreshold oscillatory neurons in the presence of noise can sensitively and
also selectively be tuned by stimulus-dependent variation of model parameters.Comment: 19 pages, 7 figure
The use of urinary proteomics in the assessment of suitability of mouse models for ageing
Ageing is a complex process characterised by a systemic and progressive deterioration of biological functions. As ageing is associated with an increased prevalence of age-related chronic disorders, understanding its underlying molecular mechanisms can pave the way for therapeutic interventions and managing complications. Animal models such as mice are commonly used in ageing research as they have a shorter lifespan in comparison to humans and are also genetically close to humans. To assess the translatability of mouse ageing to human ageing, the urinary proteome in 89 wild-type (C57BL/6) mice aged between 8–96 weeks was investigated using capillary electrophoresis coupled to mass spectrometry (CE-MS). Using age as a continuous variable, 295 peptides significantly correlated with age in mice were identified. To investigate the relevance of using mouse models in human ageing studies, a comparison was performed with a previous correlation analysis using 1227 healthy subjects. In mice and humans, a decrease in urinary excretion of fibrillar collagens and an increase of uromodulin fragments was observed with advanced age. Of the 295 peptides correlating with age, 49 had a strong homology to the respective human age-related peptides. These ortholog peptides including several collagen (N = 44) and uromodulin (N = 5) fragments were used to generate an ageing classifier that was able to discriminate the age among both wild-type mice and healthy subjects. Additionally, the ageing classifier depicted that telomerase knock-out mice were older than their chronological age. Hence, with a focus on ortholog urinary peptides mouse ageing can be translated to human ageing
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