Self-interfering wavepackets

We study the propagation of non-interacting polariton wavepackets. We show how two qualitatively different concepts of mass that arise from the peculiar polariton dispersion lead to a new type of particle-like object from non-interacting fields---much like self-accelerating beams---shaped by the Rabi coupling out of Gaussian initial states. A divergence and change of sign of the diffusive mass results in a "mass wall" on which polariton wavepackets bounce back. Together with the Rabi dynamics, this yield propagation of ultrafast subpackets and ordering of a spacetime crystal.Comment: (no movies part of this preprint

Comparison of SVM and some older classification algorithms in text classification tasks

Document classification has already been widely studied. In fact, some studies compared feature selection techniques or feature space transformation whereas some others compared the performance of different algorithms. Recently, following the rising interest towards the Support Vector Machine, various studies showed that SVM outperforms other classification algorithms. So should we just not bother about other classification algorithms and opt always for SVM We have decided to investigate this issue and compared SVM to kNN and naive Bayes on binary classification tasks. An important issue is to compare optimized versions of these algorithms, which is what we have done. Our results show all the classifiers achieved comparable performance on most problems. One surprising result is that SVM was not a clear winner, despite quite good overall performance. If a suitable preprocessing is used with kNN, this algorithm continues to achieve very good results and scales up well with the number of documents, which is not the case for SVM. As for naive Bayes, it also achieved good performance.IFIP International Conference on Artificial Intelligence in Theory and Practice - Knowledge Acquisition and Data MiningRed de Universidades con Carreras en Informática (RedUNCI

Formation of nonlinear X-waves in condensed matter systems

X-waves are an example of a localized wave packet solution of the homogeneous wave equation, and can potentially arise in any area of physics relating to wave phenomena, such as acoustics, electromagnetism, or quantum mechanics. They have been predicted in condensed matter systems such as atomic Bose-Einstein condensates in optical lattices, and were recently observed in exciton-polariton condensates. Here we show that polariton X-waves result from an interference between two separating wave packets that arise from the combination of a locally hyperbolic dispersion relation and nonlinear interactions. We show that similar X-wave structures could also be observed in expanding spin-orbit coupled Bose-Einstein condensates.Published onlin

Concordanciers : Thème et variations

International audienceThe computation of a concordance is usually determined by three parameters : the word (or linguistic pattern) to be found, the size of the context given for each token, and the way the extracts should be sorted in order to facilitate the analysis. The power of this technic lies in the visual effects it creates by aligning and grouping the contexts through the centered-column presentation and the sorting of the lines. These principles can be generalized and extended : the pattern to be found can be decomposed into several zones, and each of them can be aligned as a column, or/and can be sorted.We illustrate these proposals by the implementation of a concordancer (KWAC-LLI) specialized for corpus linguistics in a distributional semantics approach. The corpus can be analysed according to four strategies, based on the syntagmatic or paradigmatic relation between predicates and arguments. The specialized concordancer tests two new features. The first one is a table which gives a global view of the concordance, with hypertext access to the detailed contexts. The second new feature is a linguistic sort, directly derived from the "classe d'objets" theory.Le calcul d'un concordancier se définit classiquement par trois paramètres : l'expression d'un pivot, la délimitation du contexte donné pour chaque occurrence relevée du pivot, et l'organisation des extraits par un tri facilitant le dépouillement. L'efficacité propre à cette technique tient essentiellement aux effets d'alignement et de regroupement issus de la présentation du pivot sur une colonne et des tris sur le pivot et son environnement. Nous proposons donc une généralisation de la technique des concordances avec l'articulation interne du pivot en plusieurs zones, focalisant et démultipliant les possibilités d'alignement et de tri.Nous prenons appui sur cette réflexion pour développer un concordancier (KWAC-LLI) adapté aux besoins linguistiques d'une sémantique distributionnelle, en l'occurrence la théorie des classes d'objets. Une combinatoire de quatre stratégies d'exploration de corpus peut être ainsi outillée, selon que l'on part de prédicats ou d'arguments pour rechercher d'autres prédicats ou d'autres arguments. Le concordancier s'enrichit dans ce contexte de deux innovations significatives : la présentation globale et synthétique des résultats sous forme de tableau hypertexte, et le tri des lignes du tableau traduisant directement un critère de pertinence linguistique donné par la théorie des classes d'objets

Comparison of SVM and some older classification algorithms in text classification tasks

Document classification has already been widely studied. In fact, some studies compared feature selection techniques or feature space transformation whereas some others compared the performance of different algorithms. Recently, following the rising interest towards the Support Vector Machine, various studies showed that SVM outperforms other classification algorithms. So should we just not bother about other classification algorithms and opt always for SVM We have decided to investigate this issue and compared SVM to kNN and naive Bayes on binary classification tasks. An important issue is to compare optimized versions of these algorithms, which is what we have done. Our results show all the classifiers achieved comparable performance on most problems. One surprising result is that SVM was not a clear winner, despite quite good overall performance. If a suitable preprocessing is used with kNN, this algorithm continues to achieve very good results and scales up well with the number of documents, which is not the case for SVM. As for naive Bayes, it also achieved good performance.IFIP International Conference on Artificial Intelligence in Theory and Practice - Knowledge Acquisition and Data MiningRed de Universidades con Carreras en Informática (RedUNCI

Topologically driven Rabi-oscillating interference dislocation

Quantum vortices are the quantized version of classical vortices. Their center is a phase singularity or vortex core around which the flow of particles as a whole circulates and is typical in superfluids, condensates and optical fields. However, the exploration of the motion of the phase singularities in coherently-coupled systems is still underway. We theoretically analyze the propagation of an interference dislocation in the regime of strong coupling between light and matter, with strong mass imbalance, corresponding to the case of microcavity exciton-polaritons. To this end, we utilize combinations of vortex and tightly focused Gaussian beams, which are introduced through resonant pulsed pumping. We show that a dislocation originates from self-interference fringes, due to the non-parabolic dispersion of polaritons combined with moving Rabi-oscillating vortices. The morphology of singularities is analyzed in the Poincar\'{e} space for the pseudospin associated to the polariton states. The resulting beam carries orbital angular momentum with decaying oscillations due to the loss of overlap between the normal modes of the polariton system.Comment: 9 pages, 6 figure

Negative-mass effects in spin-orbit coupled Bose-Einstein condensates

Negative effective masses can be realized by engineering the dispersion relation of a variety of quantum systems. A recent experiment with spin-orbit coupled Bose-Einstein condensates has shown that a negative effective mass can halt the free expansion of the condensate and lead to fringes in the density [M. A. Khamehchi et al., Phys. Rev. Lett. 118, 155301 (2017)]. Here, we show that the underlying cause of these observations is the self-interference of the wave packet that arises when only one of the two effective mass parameters that characterize the dispersion of the system is negative. We show that spin-orbit coupled Bose-Einstein condensates may access regimes where both mass parameters controlling the propagation and diffusion of the condensate are negative, which leads to the novel phenomenon of counterpropagating self-interfering packets.EU project polaflo