La formetría aplicada a las deformidades de la columna.

La forma de la espalda es un factor importante en la evaluación clínica de varias afecciones de la columna, en particular de la escoliosis. Se describe un método de análisis de la forma de la superficie de la espalda que fue ideado para conocer la mayoría de los parámetros necesarios para evaluar el progreso de la enfermedad en tanto afecte a la forma del cuerpo. La medición de la forma de la superficie de la espalda y de las marcas anatómicas manuales se analizan a través de un sistema de ordenador-monitor en el que se escanea el plano de luz incidente sobre la espalda y desde topografía moiré. Las marcas anatómicas se llevan a cabo para definir los planos de referencia desde los cuales se comparan sucesivos análisis. Este método se emplea para estimar los ángulos de las vértebras límites y los ángulos de Cobb. Las secciones laterales muestran la cifosis y lordosis. Para los resultados se han llevado a cabo correlaciones de la asimetría lateral de la forma de la superficie con el ángulo de Cobb medido mediante radiografía. Las mediciones se llevaron a cabo en tres grupos de pacientes (47 pacientes en total). El rango osciló entre r=0.66 a r=0.88, para una p<0.001. El análisis de los resultados podría reducir en un futuro los exámenes con rayos X en el evolutivo, por lo evidenciado cuantitativamente y con inocuidad total tanto en la asimetría lateral como en la deformidad en el plano transverso.Peer Reviewe

Non-perturbative k-body to two-body commuting conversion Hamiltonians and embedding problem instances into Ising spins

An algebraic method has been developed which allows one to engineer several energy levels including the low-energy subspace of interacting spin systems. By introducing ancillary qubits, this approach allows k-body interactions to be captured exactly using 2-body Hamiltonians. Our method works when all terms in the Hamiltonian share the same basis and has no dependence on perturbation theory or the associated large spectral gap. Our methods allow problem instance solutions to be embedded into the ground energy state of Ising spin systems. Adiabatic evolution might then be used to place a computational system into it's ground state.Comment: Published versio

Entanglement and alpha entropies for a massive Dirac field in two dimensions

We present some exact results about universal quantities derived from the local density matrix, for a free massive Dirac field in two dimensions. We first find the trace of powers of the density matrix in a novel fashion, which involves the correlators of suitable operators in the sine-Gordon model. These, in turn, can be written exactly in terms of the solutions of non-linear differential equations of the Painlev\'e V type. Equipped with the previous results, we find the leading terms for the entanglement entropy, both for short and long distances, and showing that in the intermediate regime it can be expanded in a series of multiple integrals. The previous results have been checked by direct numerical calculations on the lattice, finding perfect agreement. Finally, we comment on a possible generalization of the entanglement entropy c-theorem to the alpha-entropies.Comment: Clarification in section 2, one reference added. 15 pages, 3 figure

Numerical study of the one-dimensional quantum compass model

The ground state magnetic phase diagram of the one-dimensional quantum compass model (QCM) is studied using the numerical Lanczos method. A detailed numerical analysis of the low energy excitation spectrum is presented. The energy gap and the spin-spin correlation functions are calculated for finite chains. Two kind of the magnetic long-range orders, the Neel and a type of the stripe-antiferromagnet, in the ground state phase diagram are identified. Based on the numerical analysis, the first and second order quantum phase transitions in the ground state phase diagram are identified.Comment: 6 pages, 8 figures. arXiv admin note: text overlap with arXiv:1105.211

Block Spin Density Matrix of the Inhomogeneous AKLT Model

We study the inhomogeneous generalization of a 1-dimensional AKLT spin chain model. Spins at each lattice site could be different. Under certain conditions, the ground state of this AKLT model is unique and is described by the Valence-Bond-Solid (VBS) state. We calculate the density matrix of a contiguous block of bulk spins in this ground state. The density matrix is independent of spins outside the block. It is diagonalized and shown to be a projector onto a subspace. We prove that for large block the density matrix behaves as the identity in the subspace. The von Neumann entropy coincides with Renyi entropy and is equal to the saturated value.Comment: 20 page

Entanglement Entropy dynamics in Heisenberg chains

By means of the time-dependent density matrix renormalization group algorithm we study the zero-temperature dynamics of the Von Neumann entropy of a block of spins in a Heisenberg chain after a sudden quench in the anisotropy parameter. In the absence of any disorder the block entropy increases linearly with time and then saturates. We analyze the velocity of propagation of the entanglement as a function of the initial and final anisotropies and compare, wherever possible, our results with those obtained by means of Conformal Field Theory. In the disordered case we find a slower (logarithmic) evolution which may signals the onset of entanglement localization.Comment: 15 pages, 9 figure

Entanglement and Density Matrix of a Block of Spins in AKLT Model

We study a 1-dimensional AKLT spin chain, consisting of spins $S$ in the bulk and $S/2$ at both ends. The unique ground state of this AKLT model is described by the Valence-Bond-Solid (VBS) state. We investigate the density matrix of a contiguous block of bulk spins in this ground state. It is shown that the density matrix is a projector onto a subspace of dimension $(S+1)^{2}$. This subspace is described by non-zero eigenvalues and corresponding eigenvectors of the density matrix. We prove that for large block the von Neumann entropy coincides with Renyi entropy and is equal to $\ln(S+1)^{2}$.Comment: Revised version, typos corrected, references added, 31 page

The Interspersed Spin Boson Lattice Model

We describe a family of lattice models that support a new class of quantum magnetism characterized by correlated spin and bosonic ordering [Phys. Rev. Lett. 112, 180405 (2014)]. We explore the full phase diagram of the model using Matrix-Product-State methods. Guided by these numerical results, we describe a modified variational ansatz to improve our analytic description of the groundstate at low boson frequencies. Additionally, we introduce an experimental protocol capable of inferring the low-energy excitations of the system by means of Fano scattering spectroscopy. Finally, we discuss the implementation and characterization of this model with current circuit-QED technology.Comment: Submitted to EPJ ST issue on "Novel Quantum Phases and Mesoscopic Physics in Quantum Gases

Entanglement properties and moment distributions of a system of hard-core anyons on a ring

We study the one-particle von Neumann entropy of a system of N hard-core anyons on a ring. The entropy is found to have a clear dependence on the anyonic parameter which characterizes the generalized fractional statistics described by the anyons. This confirms the entanglement as a valuable measure to investigate topological properties of quantum states. Furthermore, we determine analytically the large N asymptotics of the anyonic one-particle density matrix. The formula presented here generalizes the Lenard formula obtained for a system of N hard-core bosons. Finally, we present a numerical analysis which confirms the analytical results and provides additional insight into the problem under consideration.Comment: 5 pages, 3 eps figures. v2: Fig 3 changed, Eq 13 changed, minor corrections. References adde