Guaranteed emergence of genuine entanglement in 3-qubit evolving systems

Multipartite entanglement has been shown to be of particular relevance for a better understanding and exploitation of the dynamics and flow of entanglement in multiparty systems. This calls for analysis aimed at identifying the appropriate processes that guarantee the emergence of multipartite entanglement in a wide range of scenarios. Here we carry on such analysis considering a system of two initially entangled qubits, one of which is let to interact with a third qubit according to an arbitrary unitary evolution. We establish necessary and sufficient conditions on the corresponding Kraus operators, to discern whether the evolved state pertains to either one of the classes of 3-qubit pure states that exhibit some kind of entanglement, namely biseparable, W-, and GHZ- genuine entangled classes. Our results provide a classification of the Kraus operators according to their capacity of producing 3-qubit entanglement, and pave the way for extending the analysis to larger systems and determining the particular interactions that must be implemented in order to create, enhance and distribute entanglement in a specific manner.Comment: Two new subsections included. Accepted for publication in The European Physical Journal

Horizontal inequality in the transition to upper secondary education in Spain

Effectively maintained inequality theory posits that a reduction in vertical inequality following the expansion of a level of education will be compensated by an increase in horizontal inequality. Although this theory has been intensely studied in various countries, it has barely been explored in the Spanish case. To fill this gap, I use data from the Survey on the Transition from Education/Training to Labour Market Insertion and analyse the sample of students who completed compulsory education in 2001, right after the expansion of upper secondary education (baccalaureate) in Spain. I study two forms of horizontal inequality: the type of education enrolled in (including which modality is preferred in the academic track) and the time for completion of the academic track. I report that the saturation of baccalaureate in the choice against vocational education triggered substantial inequalities in the preference for the most rewarding modalities of baccalaureate: socioeconomically advantaged students preferred the natural sciences and technology, while disadvantaged students preferred the social sciences, humanities, and arts. In turn, inequality in the time for completion of baccalaureate is mostly vertical as the two most likely results for all socioeconomic groups are to complete baccalaureate in two years or not complete it at all.La teoria de la desigualtat efectivament mantinguda postula que la reducció de la desigualtat vertical després de l'expansió d'un nivell educatiu es veurà compensada per un augment de la desigualtat horitzontal. Encara que aquesta teoria ha estat intensament estudiada en diversos països, amb prou feines ha estat explorada en el cas espanyol. Per omplir aquest buit, utilitzo dades de l'Enquesta de transició educativa-formativa i inserció laboral i analitzo la mostra d'estudiants que van acabar l'educació secundària obligatòria el 2001, just després de l'expansió de l'educació secundària superior a Espanya. Estudio dues formes de desigualtat horitzontal: el tipus d'ensenyament cursat (que inclou la modalitat preferida en l'itinerari acadèmic) i el temps invertit en la finalització de l'itinerari acadèmic. Demostro que la saturació del batxillerat en l'elecció davant la formació professional va desencadenar desigualtats substancials en la preferència per les modalitats de batxillerat més atractives: els estudiants d'extracció social alta van preferir Ciències Naturals i Tecnologia, mentre que els estudiants desfavorits van preferir Ciències Socials, Arts i Humanitats. Al seu torn, la desigualtat en el temps invertit en la finalització del batxillerat és majoritàriament vertical, ja que els dos resultats més probables per a tots els grups socioeconòmics són acabar el batxillerat en dos anys o no acabar-lo.La teoría de la desigualdad efectivamente mantenida postula que la reducción de la desigualdad vertical tras la expansión de un nivel educativo se verá compensada por un aumento de la desigualdad horizontal. Aunque esta teoría ha sido intensamente estudiada en varios países, apenas ha sido explorada en el caso español. Para llenar este vacío, utilizo datos de la Encuesta de transición educativa-formativa e inserción laboral y analizo la muestra de estudiantes que terminaron la educación secundaria obligatoria en 2001, justo después de la expansión de la educación secundaria superior en España. Estudio dos formas de desigualdad horizontal: el tipo de enseñanza cursada (que incluye la modalidad preferida en el itinerario académico) y el tiempo invertido en la finalización del itinerario académico. Demuestro que la saturación del bachillerato en la elección frente a la formación profesional desencadenó desigualdades sustanciales en la preferencia por las modalidades de bachillerato más atractivas: los estudiantes de extracción social alta prefirieron Ciencias Naturales y Tecnología, mientras que los estudiantes desfavorecidos prefirieron Ciencias Sociales, Artes y Humanidades. A su vez, la desigualdad en el tiempo invertido en la finalización del bachillerato es mayoritariamente vertical, ya que los dos resultados más probables para todos los grupos socioeconómicos son terminar el bachillerato en dos años o no terminarlo

Month of birth and cognitive effort: a laboratory study of the relative age effect among fifth graders

All around the world school entry cohorts are organized on an annual calendar, so that the age of students in the same cohort differs up to one year. It is a well-established finding that this age gap entails a consequential (dis)advantage for academic performance referred to as the relative age effect (RAE). This study contributes to a recent strand of research that has turned to investigate the RAE on non-academic outcomes such as personality traits. An experimental setup is used to assess the willingness to exert cognitive effort in a sample of 798 fifth grade students enrolled in the Spanish educational system, characterized by strict enrolment rules. After controlling for cognitive ability, we observe that older students outwork their youngest peers by two-fifths of a standard deviation, but only when rewards for performance are in place. Implications for sociological research on educational inequality and policy are discussed.This research has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 758600)

Roles of Bond Alternation in Magnetic Phase Diagram of RMnO3

In order to investigate nature of the antiferromagnetic structures in perovskite RMnO3, we study a Heisenberg J1-J2 model with bond alternation using analytical and numerical approaches. The magnetic phase diagram which includes incommensurate spiral states and commensurate collinear states is reproduced. We discuss that the magnetic structure with up-up-down-down spin configuration (E-type structure) and the ferroelectricity emerge cooperatively to stabilize this phase. Magnetoelastic couplings are crucial to understand the magnetic and electric phase diagram of RMnO3.Comment: 5 pages, 6 figure

A hierarchy of bound states in the 1D ferromagnetic Ising chain CoNb2_2O6_6 investigated by high resolution time-domain terahertz spectroscopy

Kink bound states in the one dimensional ferromagnetic Ising chain compound CoNb$_2$O$_6$ have been studied using high resolution time-domain terahertz spectroscopy in zero applied magnetic field. When magnetic order develops at low temperature, nine bound states of kinks become visible. Their energies can be modeled exceedingly well by the Airy function solutions to a 1D Schr\"odinger equation with a linear confining potential. This sequence of bound states terminates at a threshold energy near two times the energy of the lowest bound state. Above this energy scale we observe a broad feature consistent with the onset of the two particle continuum. At energies just below this threshold we observe a prominent excitation that we interpret as a novel bound state of bound states -- two pairs of kinks on neighboring chains

Electric-dipole active two-magnon excitation in {\textit{ab}} spiral spin phase of a ferroelectric magnet Gd0.7_{\textbf{0.7}}Tb0.3_{\textbf{0.3}}MnO3_{\textbf 3}

A broad continuum-like spin excitation (1--10 meV) with a peak structure around 2.4 meV has been observed in the ferroelectric $ab$ spiral spin phase of Gd$_{0.7}$Tb$_{0.3}$MnO$_3$ by using terahertz (THz) time-domain spectroscopy. Based on a complete set of light-polarization measurements, we identify the spin excitation active for the light $E$ vector only along the a-axis, which grows in intensity with lowering temperature even from above the magnetic ordering temperature but disappears upon the transition to the $A$-type antiferromagnetic phase. Such an electric-dipole active spin excitation as observed at THz frequencies can be ascribed to the two-magnon excitation in terms of the unique polarization selection rule in a variety of the magnetically ordered phases.Comment: 11 pages including 3 figure