Are collisions with neutral hydrogen important for modelling the Second Solar Spectrum of Ti I and Ca II ?

The physical interpretation of scattering line polarization offers a novel diagnostic window for exploring the thermal and magnetic structure of the quiet regions of the solar atmosphere. Here we evaluate the impact of isotropic collisions with neutral hydrogen atoms on the scattering polarization signals of the 13 lines of multiplet 42 of Ti I and on those of the K line and of the IR triplet of Ca II, with emphasis on the collisional transfer rates between nearby J-levels. To this end, we calculate the linear polarization produced by scattering processes considering realistic multilevel models and solving the statistical equilibrium equations for the multipolar components of the atomic density matrix. We confirm that the lower levels of the 13 lines of multiplet 42 of Ti I are completely depolarized by elastic collisions. We find that upper-level collisional depolarization turns out to have an unnoticeable impact on the emergent linear polarization amplitudes, except for the {\lambda 4536 line for which it is possible to notice a rather small depolarization caused by the collisional transfer rates. Concerning the Ca II lines, we show that the collisional rates play no role on the polarization of the upper level of the K line, while they have a rather small depolarizing effect on the atomic polarization of the metastable lower levels of the Ca II IR triplet.Comment: Accepted for publication in Astronomy and Astrophysic

Quantum error correction may delay, but also cause, entanglement sudden death

Dissipation may cause two initially entangled qubits to evolve into a separable state in a finite time. This behavior is called entanglement sudden death (ESD). We study to what extent quantum error correction can combat ESD. We find that in some cases quantum error correction can delay entanglement sudden death but in other cases quantum error correction may cause ESD for states that otherwise do not suffer from it. Our analysis also shows that fidelity may not be the best measure to compare the efficiency of different error correction codes since the fidelity is not directly coupled to a state's remaining entanglement.Comment: 3 figure

Estimating the magnetic field strength from magnetograms

A properly calibrated longitudinal magnetograph is an instrument that measures circular polarization and gives an estimation of the magnetic flux density in each observed resolution element. This usually constitutes a lower bound of the field strength in the resolution element, given that it can be made arbitrarily large as long as it occupies a proportionally smaller area of the resolution element and/or becomes more transversal to the observer and still produce the same magnetic signal. Yet, we know that arbitrarily stronger fields are less likely --hG fields are more probable than kG fields, with fields above several kG virtually absent-- and we may even have partial information about its angular distribution. Based on a set of sensible considerations, we derive simple formulae based on a Bayesian analysis to give an improved estimation of the magnetic field strength for magnetographs.Comment: 8 pages, 7 figures, accepted for publication in A&

El estado de esfuerzos durante el Terciario en la Depresión de Arnedo (La Rioja)

La aplicación de los métodos de analisis estadisticos en microtectónica frágil a la fracturación a escala microestructural de los materiales terciarios de la Depresión de Arnedo (La Rioja) ha dado como resultado la existencia de un régimen de compresión uniaxial y desgarre con el ejeu, horizontal en dirección 000-020, que se extiende al menos hasta el Mioceno inferior (Ageniense)

El estado de esfuerzos durante el Terciario en la Depresión de Arnedo (La Rioja)

La aplicación de los métodos de analisis estadisticos en microtectónica frágil a la fracturación a escala microestructural de los materiales terciarios de la Depresión de Arnedo (La Rioja) ha dado como resultado la existencia de un régimen de compresión uniaxial y desgarre con el ejeu, horizontal en dirección 000-020, que se extiende al menos hasta el Mioceno inferior (Ageniense)

Detecting non-locality in multipartite quantum systems with two-body correlation functions

Bell inequalities define experimentally observable quantities to detect non-locality. In general, they involve correlation functions of all the parties. Unfortunately, these measurements are hard to implement for systems consisting of many constituents, where only few-body correlation functions are accessible. Here we demonstrate that higher-order correlation functions are not necessary to certify nonlocality in multipartite quantum states by constructing Bell inequalities from one- and two-body correlation functions for an arbitrary number of parties. The obtained inequalities are violated by some of the Dicke states, which arise naturally in many-body physics as the ground states of the two-body Lipkin-Meshkov-Glick Hamiltonian.Comment: 10 pages, 2 figures, 1 tabl