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

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

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

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

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

Comparative effects of macro-sized aluminum oxide and aluminum oxide nanoparticles on erythrocyte hemolysis: influence of cell source, temperature and size

Al2O3 is the most abundantly produced nanomaterial and has been used in diverse fields, including the medical, military and industrial sectors. As there are concerns about the health effects of nanoparticles, it is important to understand how they interact with cells, and specifically with red blood cells. The hemolysis induced by three commercial nano-sized aluminum oxide particles (nanopowder 13 nm, nanopowder <50 nm and nanowire 2-6 nm × 200-400 nm) was compared to aluminum oxide and has been studied on erythrocytes from humans, rats and rabbits, in order to elucidate the mechanism of action and the influence of size and shape on hemolytic behavior. The concentrations inducing 50% hemolysis (HC50) were calculated for each compound studied. The most hemolytic aluminum oxide particles were of nanopowder 13, followed by nanowire and nanopowder 50. The addition of albumin to PBS induced a protective effect on hemolysis in all the nano-forms of Al2O3, but not on Al2O3. The drop in HC50 correlated to a decrease in nanomaterial size, which was induced by a reduction of aggregation Aluminum oxide nanoparticles are less hemolytic than other oxide nanoparticles, and behave differently depending on the size and shape of the nanoparticles. The hemolytic behavior of aluminum oxide nanoparticles differs from that of aluminum oxide

The Problem of Large Leptonic Mixing

Unlike in the quark sector where simple $S_3$ permutation symmetries can generate the general features of quark masses and mixings, we find it impossible (under conditions of hierarchy for the charged leptons and without considering the see-saw mechanism or a more elaborate extension of the SM) to guarantee large leptonic mixing angles with any general symmetry or transformation of only known particles. If such symmetries exist, they must be realized in more extended scenarios.Comment: RevTeX, 4 pages, no figure

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