Finite-size scaling exponents and entanglement in the two-level BCS model

We analyze the finite-size properties of the two-level BCS model. Using the continuous unitary transformation technique, we show that nontrivial scaling exponents arise at the quantum critical point for various observables such as the magnetization or the spin-spin correlation functions. We also discuss the entanglement properties of the ground state through the concurrence which appears to be singular at the transition.Comment: 4 pages, 3 figures, published versio

Violation of area-law scaling for the entanglement entropy in spin 1/2 chains

Entanglement entropy obeys area law scaling for typical physical quantum systems. This may naively be argued to follow from locality of interactions. We show that this is not the case by constructing an explicit simple spin chain Hamiltonian with nearest neighbor interactions that presents an entanglement volume scaling law. This non-translational model is contrived to have couplings that force the accumulation of singlet bonds across the half chain. Our result is complementary to the known relation between non-translational invariant, nearest neighbor interacting Hamiltonians and QMA complete problems.Comment: 9 pages, 4 figure

Renormalization group transformations on quantum states

We construct a general renormalization group transformation on quantum states, independent of any Hamiltonian dynamics of the system. We illustrate this procedure for translational invariant matrix product states in one dimension and show that product, GHZ, W and domain wall states are special cases of an emerging classification of the fixed points of this coarse--graining transformation.Comment: 5 pages, 2 figur

Continuous unitary transformations and finite-size scaling exponents in the Lipkin-Meshkov-Glick model

We analyze the finite-size scaling exponents in the Lipkin-Meshkov-Glick model by means of the Holstein-Primakoff representation of the spin operators and the continuous unitary transformations method. This combination allows us to compute analytically leading corrections to the ground state energy, the gap, the magnetization, and the two-spin correlation functions. We also present numerical calculations for large system size which confirm the validity of this approach. Finally, we use these results to discuss the entanglement properties of the ground state focusing on the (rescaled) concurrence that we compute in the thermodynamical limit.Comment: 20 pages, 9 figures, published versio

Half the entanglement in critical systems is distillable from a single specimen

We establish that the leading critical scaling of the single-copy entanglement is exactly one half of the entropy of entanglement of a block in critical infinite spin chains in a general setting, using methods of conformal field theory. Conformal symmetry imposes that the single-copy entanglement for critical many-body systems scales as E_1(\rho_L)=(c/6) \log L- (c/6) (\pi^2/\log L) + O(1/L), where L is the number of constituents in a block of an infinite chain and c corresponds to the central charge. This proves that from a single specimen of a critical chain, already half the entanglement can be distilled compared to the rate that is asymptotically available. The result is substantiated by a quantitative analysis for all translationally invariant quantum spin chains corresponding to general isotropic quasi-free fermionic models. An analytic example of the XY model shows that away from criticality the above simple relation is only maintained near the quantum phase transition point.Comment: 4 pages RevTeX, 1 figure, final versio

¿Existe alguna relación entre la capacidad de movimiento funcional y el estado ponderal? Un estudio en escolares españoles

Indexación: Scopus.Background: to examine relations between functional movement patterns and weight status in Spanish primary school children and to determine the differences between sexes. Methods: three hundred and thirty-three, 6-13 years old children (164 boys and 169 girls), participated in this study. The main outcome measures were the body mass index (BMI) and the Functional Movement Screen™ (FMS). Children were classified as normal weight (NW), overweight (OV) or obese (OB) according to international cut-offs. Results: total FMS score was negatively correlated with BMI (p < 0.001). FMS score was different between children from NW, OV and OB groups (p = 0.001), lower with the increased BMI (p < 0.001 between all groups). Significant differences (p < 0.05) between NW, OV and OB were found in deep squat, hurdle step, in-line lunge, shoulder mobility, straight leg-raise and push-up tests. As for the sex differences, girls obtained higher scores (p < 0.05) in in-line lunge, shoulder mobility and straight leg-raise, whereas boys did it in push-up (p = 0.044) test. Conclusions: these results confirm that total FMS score significantly and inversely correlates with BMI in a group of 333 school-age children. As for the sex differences, girls outperform boys in movements requiring flexibility and balance, whilst boys outperform girls in tests where muscular strength is required. © 2018 SENPE and Arán Ediciones S.L.Introducción: examinar la relación entre los patrones de movimiento funcional y el estado ponderal en escolares españoles, determinando también la infl uencia de la variable sexo. Métodos: trescientos treinta y tres niños de 6-13 años de edad (164 niños y 169 niñas), participaron voluntariamente en este estudio. Las variables objeto de estudio fueron el índice de masa corporal (IMC) y la batería de test Functional Movement ScreenTM (FMS). Los niños fueron clasifi cados como normopeso (NW), sobrepeso (OV) y obesos (OB) de acuerdo con los puntos de corte internacionales. Resultados: la puntuación total en el FMS correlacionó de forma negativa y signifi cativa con el IMC (p < 0,001). La puntuación en FMS fue diferente entre las categorías de peso (p = 0,001), hallando un peor rendimiento en FMS conforme aumenta el IMC (p < 0,001 entre todos los grupos). Se hallaron diferencias signifi cativas (p < 0,05) entre NW, OV y OB en los test de deep squat, hurdle step, in-line lunge, shoulder mobility, straight leg-raise and push-up. En cuanto a las diferencias por sexo, las chicas obtuvieron puntuaciones más altas en FMS (p < 0,05) en los test in-line lunge, shoulder mobility and straight leg-raise; mientras los chicos obtuvieron puntuaciones superiores en el test de push-up (p = 0,044). Conclusiones: los resultados confi rman que la puntuación total en el FMS correlaciona signifi cativa y negativamente con el IMC en este grupo de 333 escolares. En cuanto a la infl uencia del sexo, las chicas obtuvieron mayor puntuación que los chicos en los test que requerían fl exibilidad y equilibrio, mientras los chicos fueron superiores en los test en los que predominaba la fuerza muscular.https://www.nutricionhospitalaria.org/index.php/articles/01670/show#

Valence Bond Entanglement Entropy

We introduce for SU(2) quantum spin systems the Valence Bond Entanglement Entropy as a counting of valence bond spin singlets shared by two subsystems. For a large class of antiferromagnetic systems, it can be calculated in all dimensions with Quantum Monte Carlo simulations in the valence bond basis. We show numerically that this quantity displays all features of the von Neumann entanglement entropy for several one-dimensional systems. For two-dimensional Heisenberg models, we find a strict area law for a Valence Bond Solid state and multiplicative logarithmic corrections for the Neel phase.Comment: 4 pages, 3 figures, v2: small corrections, published versio

GHZ extraction yield for multipartite stabilizer states

Let $|\Psi>$ be an arbitrary stabilizer state distributed between three remote parties, such that each party holds several qubits. Let $S$ be a stabilizer group of $|\Psi>$. We show that $|\Psi>$ can be converted by local unitaries into a collection of singlets, GHZ states, and local one-qubit states. The numbers of singlets and GHZs are determined by dimensions of certain subgroups of $S$. For an arbitrary number of parties $m$ we find a formula for the maximal number of $m$-partite GHZ states that can be extracted from $|\Psi>$ by local unitaries. A connection with earlier introduced measures of multipartite correlations is made. An example of an undecomposable four-party stabilizer state with more than one qubit per party is given. These results are derived from a general theoretical framework that allows one to study interconversion of multipartite stabilizer states by local Clifford group operators. As a simple application, we study three-party entanglement in two-dimensional lattice models that can be exactly solved by the stabilizer formalism.Comment: 12 pages, 1 figur

Radiation and magnetic field effects on new semiconductor power devices for HL-LHC experiments

The radiation hardness of commercial Silicon Carbide and Gallium Nitride power MOSFETs is presented in this paper, for Total Ionizing Dose effects and Single Event Effects, under gamma, neutrons, protons and heavy ions. Similar tests are discussed for commercial DC-DC converters, also tested in operation under magnetic field