4,151 research outputs found
Collapse and revival oscillations as a probe for the tunneling amplitude in an ultra-cold Bose gas
We present a theoretical study of the quantum corrections to the revival time
due to finite tunneling in the collapse and revival of matter wave interference
after a quantum quench. We study hard-core bosons in a superlattice potential
and the Bose-Hubbard model by means of exact numerical approaches and
mean-field theory. We consider systems without and with a trapping potential
present. We show that the quantum corrections to the revival time can be used
to accurately determine the value of the hopping parameter in experiments with
ultracold bosons in optical lattices.Comment: 10 pages, 12 figures, typos in section 3A correcte
Non-Poissonian statistics from Poissonian light sources with application to passive decoy state quantum key distribution
We propose a method to prepare different non-Poissonian signal pulses from
sources of Poissonian photon number distribution using only linear optical
elements and threshold photon detectors. This method allows a simple passive
preparation of decoy states for quantum key distribution. We show that the
resulting key rates are comparable to the performance of active choices of
intensities of Poissonian signals.Comment: 7 pages, 3 figures, accepted for publication in Opt. Let
Global Growth and Trends of In-Body Communication Research—Insight From Bibliometric Analysis
A bibliometric analysis was conducted to examine research on in-body communication. This study aimed to assess the research growth in different countries, identify influential authors for potential international collaboration, investigate research challenges, and explore future prospects for in-body communication. A total of 148 articles written in English from journals and conference proceedings were gathered from the Scopus database. These articles cover the period from 2006 until August 2023. VOS Viewer 1.6.19 and Tableau Cloud were used to analyze the data. The analysis reveals that research on in-body communication has shown fluctuations but overall tends to increase. The United States, Finland, and Japan were identified as the leading countries (top three) in terms of publication quantity, while researchers from Norway, Finland, and Morocco received the highest number of citations. The University of Oulu in Finland has emerged as a productive institution in this field. Collaborative research opportunities exist with the countries mentioned above or with authors who have expertise in this topic. The dominant research topic within this field pertains to ultra-wideband (UWB) technology. One of the future challenges in this field is the exploration of optical wireless communication (OWC) as a potential communication medium for in-body devices, such as electronic devices implanted in the human body. This includes improving performance to meet the requirements for in-body communication devices. Additionally, this paper provides further insights into the progress of research on OWC for in-body communication conducted in our laboratory
Passive sources for the Bennett-Brassard 1984 quantum key distribution protocol with practical signals
Most experimental realizations of quantum key distribution are based on the
Bennett-Brassard 1984 (so-called BB84) protocol. In a typical optical
implementation of this scheme, the sender uses an active source to produce the
required BB84 signal states. While active state preparation of BB84 signals is
a simple and elegant solution in principle, in practice passive state
preparation might be desirable in some scenarios, for instance, in those
experimental setups operating at high transmission rates. Passive schemes might
also be more robust against side-channel attacks than active sources. Typical
passive devices involve parametric down-conversion. In this paper, we show that
both coherent light and practical single photon sources are also suitable for
passive generation of BB84 signal states. Our method does not require any
external-driven element, but only linear optical components and photodetectors.
In the case of coherent light, the resulting key rate is similar to the one
delivered by an active source. When the sender uses practical single photon
sources, however, the distance covered by a passive transmitter might be longer
than the one of an active configuration.Comment: 14 pages, 11 figure
Formació i tecnologies de la traducció
Aquest número de la Revista Tradumàtica proposa una reflexió sobre la necessària imbricació entre les tecnologies i la formació de traductors. L’objectiu és presentar punts de vista diferents i sovint complementaris relacionats amb els diversos papers que hi entren en joc: interessa saber el que pensen les persones responsables de la formació i conèixer quines característiques té l’oferta docent, però també convé veure com es situen els estudiants. D’igual manera volem pensar en el futur, sense perdre de vista el present d’un context tan àgil i canviant com el que es descriu aquí.Este número de la Revista Tradumàtica propone una reflexión sobre la necesaria imbricación entre las tecnologías y la formación de traductores. El objetivo es presentar puntos de vista diferentes y a menudo complementarios relacionados con los diversos papeles que entran en juego: interesa saber lo que piensan las personas responsables de la formación y conocer las características de la oferta docente, pero también conviene ver como se sitúan los estudiantes. De igual manera queremos pensar en el futuro, pero sin perder de vista el presente de un contexto tan ágil y cambiante como el que aquí se describe
Isothermal Titration Calorimetry and Transmission Electron Microscopy of Main-Chain Viologen Polymer Containing Bromide as Counerions
Polyelectrolytes are an important class of macromolecules that contain dissociable ionic groups. When introduced into polar solvent, usually the universal solvent water, dissociation takes place so that electrically charged macromolecule is suspended in solution. The electrostatic interaction is operative between ionized groups inside the macromolecule, between the macromolecules, between the counterions, and between the macromolecule and counterion. Since this interaction is characterized by its long-range nature, the solution exhibits various interesting properties including the polyelectrolyte behavior very different from solutions of neutral polymers
Influencia de los modelos intuitivos en la comprensión de la multiplicación y la división
Since the stdy by Fischbein et al. (1985) which suggested that children develop intuitive models about multiplication and division early, much research has offered data that corroborate these models. In this study we analyze the differential weight of the models in three kid of task: algorithms, problem solving, and problem posing. We included two age groups (1st of ESO and 8th of EGB), and three kid of quantities (whole numbers, decimals and fractions). The results indicated that the intuitive models did not have the same differential weight for the different tasks. For instance, the problem posing task did not seem suited to the conditions under which the intuitive models act. Likewise, the presence of quantities that failed to observe one or more restrictions of the models did not have a negative influence. In contrast, the errors committed in the two remaining tasks were almost exclusively due to the application of the intuitive rules.A partir del trabajo de Fischbein et al. (1985) que sugiere que los niños construyen tempranamente modelos intuitivos sobre la multiplicación y división, numerosas investigaciones han ofrecido datos consistentes con estos modelos. En este estudio analizamos el peso diferencial de los modelos en tres tipos de tareas: resolver algoritmes, resolver problemas y plantear problemas. Hemos incluido también dos grupos de edad (1º de ESO y 8º de EGB), asi como tres tipos de cantidades (enteros, decimales y fracciones). LoS resultados indicaron que los modelos intuitivos no tuvieron el mismo peso diferencial en las diferentes tareas. Por ejemplo, la tarea de plantear problemas no parecía reunir las condiciones bajo las que actúan los modelos intuitivos. Asimismo, la presencia de cantidades que alteraban una o más imposiciones de los modelos no influyó negativamente. Por el contrario, los errores de las dos tareas restantes se debieron a la aplicación de las reglas intuitivas
Neutron rich nuclei in density dependent relativistic Hartree-Fock theory with isovector mesons
Density dependent relativistic Hartree-Fock theory has been extended to
describe properties of exotic nuclei. The effects of Fock exchange terms and of
pi - and rho - meson contributions are discussed. These effects are found to be
more important for neutron rich nuclei than for nuclei near the valley of
stability.Comment: 10 pages, 5 figures, LaTeX, macro packages graphicx and time
Upper bounds for the secure key rate of decoy state quantum key distribution
The use of decoy states in quantum key distribution (QKD) has provided a
method for substantially increasing the secret key rate and distance that can
be covered by QKD protocols with practical signals. The security analysis of
these schemes, however, leaves open the possibility that the development of
better proof techniques, or better classical post-processing methods, might
further improve their performance in realistic scenarios. In this paper, we
derive upper bounds on the secure key rate for decoy state QKD. These bounds
are based basically only on the classical correlations established by the
legitimate users during the quantum communication phase of the protocol. The
only assumption about the possible post-processing methods is that double click
events are randomly assigned to single click events. Further we consider only
secure key rates based on the uncalibrated device scenario which assigns
imperfections such as detection inefficiency to the eavesdropper. Our analysis
relies on two preconditions for secure two-way and one-way QKD: The legitimate
users need to prove that there exists no separable state (in the case of
two-way QKD), or that there exists no quantum state having a symmetric
extension (one-way QKD), that is compatible with the available measurements
results. Both criteria have been previously applied to evaluate single-photon
implementations of QKD. Here we use them to investigate a realistic source of
weak coherent pulses. The resulting upper bounds can be formulated as a convex
optimization problem known as a semidefinite program which can be efficiently
solved. For the standard four-state QKD protocol, they are quite close to known
lower bounds, thus showing that there are clear limits to the further
improvement of classical post-processing techniques in decoy state QKD.Comment: 10 pages, 3 figure
Tri-Bimaximal Neutrino Mixing from Discrete Symmetry in Extra Dimensions
We discuss a particularly symmetric model of neutrino mixings where, with
good accuracy, the atmospheric mixing angle theta_{23} is maximal, theta_{13}=0
and the solar angle satisfies sin^2(theta_{12})=1/3 (Harrison-Perkins-Scott
(HPS) matrix). The discrete symmetry A_4 is a suitable symmetry group for the
realization of this type of model. We construct a model where the HPS matrix is
exactly obtained in a first approximation without imposing ad hoc relations
among parameters. The crucial issue of the required VEV alignment in the scalar
sector is discussed and we present a natural solution of this problem based on
a formulation with extra dimensions. We study the corrections from higher
dimensionality operators allowed by the symmetries of the model and discuss the
conditions on the cut-off scales and the VEVs in order for these corrections to
be completely under control. Finally, the observed hierarchy of charged lepton
masses is obtained by assuming a larger flavour symmetry. We also show that,
under general conditions, a maximal theta_{23} can never arise from an exact
flavour symmetry.Comment: 24 pages, 1 figure, misprints corrected and references adde
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