Correlation functions of a Lieb-Liniger Bose gas

The ground-state correlation functions of a one-dimensional homogeneous Bose system described by the Lieb-Liniger Hamiltonian are investigated by using exact quantum Monte Carlo techniques. This article is an extension of a previous study published in Phys. Rev. A {\bf 68}, 031602 (2003). New results on the local three-body correlator as a function of the interaction strength are included and compared with the measured value from three-body loss experiments. We also carry out a thorough study of the short- and long-range behavior of the one-body density matrix.Comment: 10 pages, 8 figures, contribution to Cortona BEC JPB special issu

Universal resources for approximate and stochastic measurement-based quantum computation

We investigate which quantum states can serve as universal resources for approximate and stochastic measurement-based quantum computation, in the sense that any quantum state can be generated from a given resource by means of single-qubit (local) operations assisted by classical communication. More precisely, we consider the approximate and stochastic generation of states, resulting e.g. from a restriction to finite measurement settings or from possible imperfections in the resources or local operations. We show that entanglement-based criteria for universality obtained for the exact, deterministic case can be lifted to the much more general approximate, stochastic case, moving from the idealized situation considered in previous works, to the practically relevant context of non-perfect state preparation. We find that any entanglement measure fulfilling some basic requirements needs to reach its maximum value on some element of an approximate, stochastic universal family of resource states, as the resource size grows. This allows us to rule out various families of states as being approximate, stochastic universal. We provide examples of resources that are efficient approximate universal, but not exact deterministic universal. We also study the robustness of universal resources for measurement-based quantum computation under realistic assumptions about the (imperfect) generation and manipulation of entangled states, giving an explicit expression for the impact that errors made in the preparation of the resource have on the possibility to use it for universal approximate and stochastic state preparation. Finally, we discuss the relation between our entanglement-based criteria and recent results regarding the uselessness of states with a high degree of geometric entanglement as universal resources.Comment: 17 pages; abstract shortened with respect to the published version to respect the arXiv limit of 1,920 character

Enabling science with Gaia observations of naked-eye stars

ESA's Gaia space astrometry mission is performing an all-sky survey of stellar objects. At the beginning of the nominal mission in July 2014, an operation scheme was adopted that enabled Gaia to routinely acquire observations of all stars brighter than the original limit of G~6, i.e. the naked-eye stars. Here, we describe the current status and extent of those observations and their on-ground processing. We present an overview of the data products generated for G<6 stars and the potential scientific applications. Finally, we discuss how the Gaia survey could be enhanced by further exploiting the techniques we developed.Comment: 16 pages, 8 figures. Submitted for the proceedings of the 2016 SPIE Astronomical Instrumentation and Telescopes conference (SPIE 9904

Diferenciación morfotécnica y diacronismo en el Paleolítico medio catalán

[Resumen] Se hace una revisión crítica del "musteriense", su historia, evolución del término, sistemas de análisis y se plantea la alternativa del "continuum evolutivo dinámico" para su estudio. Aplicamos la tipología analítica y el sistema 1ógico analítico al estudio del Paleolítico Medio catalán, trabajando con los lugares de ocupaci6n de Avetllaners y Diable Coix (La Selva), L'Arbreda H-43 - (Serinya), Ermitons (Garrotxa), Abric Romaní C4 Y'C9 (Anoia) y Les Fonts (Segria). Como resultado de la aplicación de este sistema de trabajo se óbtiene información que permite correlacionar lugares de ocupación en abrigo o cueva con los situados al aire libre, así como interpretar, a través de hip6tesis contrastadas, la funcionalidad y cronología de los yacimientos del Paleolítico Medio catalán.[Abstract] The purpose of this paper is to realize a critical revision of Mousterian evolution of this term, its history and analytic sistems,the alternative by "continuum evolutivo dinámico" is stablished for studying it. We apply the logical-analytical sistem to study middle catalan Paleolithic. We work with the placeof ocuppations at Avetllaners y Diable Coix (La Selva), L'Arbreda H-43 (Serinya), Ermitons (Garrotxa), Abric Romaní C4 y C9 (Anoia) y Les Fonts {Segria) The information that we obtain after the application oí this sistem work permit us, to correlate place oí ocuppations in shelter or cave with other in open air as well as we can interpret, by contrasted hypothesis, the funcionality and t~e cronology of sites in the Middle catalan Paleolithi

Class of PPT bound entangled states associated to almost any set of pure entangled states

We analyze a class of entangled states for bipartite $d \otimes d$ systems, with $d$ non-prime. The entanglement of such states is revealed by the construction of canonically associated entanglement witnesses. The structure of the states is very simple and similar to the one of isotropic states: they are a mixture of a separable and a pure entangled state whose supports are orthogonal. Despite such simple structure, in an opportune interval of the mixing parameter their entanglement is not revealed by partial transposition nor by the realignment criterion, i.e. by any permutational criterion in the bipartite setting. In the range in which the states are Positive under Partial Transposition (PPT), they are not distillable; on the other hand, the states in the considered class are provably distillable as soon as they are Nonpositive under Partial Transposition (NPT). The states are associated to any set of more than two pure states. The analysis is extended to the multipartite setting. By an opportune selection of the set of multipartite pure states, it is possible to construct mixed states which are PPT with respect to any choice of bipartite cuts and nevertheless exhibit genuine multipartite entanglement. Finally, we show that every $k$-positive but not completely positive map is associated to a family of nondecomposable maps.Comment: 12 pages, 3 figures. To appear in Phys. Rev.

Intrinsic limitations of inverse inference in the pairwise Ising spin glass

We analyze the limits inherent to the inverse reconstruction of a pairwise Ising spin glass based on susceptibility propagation. We establish the conditions under which the susceptibility propagation algorithm is able to reconstruct the characteristics of the network given first- and second-order local observables, evaluate eventual errors due to various types of noise in the originally observed data, and discuss the scaling of the problem with the number of degrees of freedom