59 research outputs found
Scaling of entanglement between separated blocks in spin chains at criticality
We compute the entanglement between separated blocks in certain spin models
showing that at criticality this entanglement is a function of the ratio of the
separation to the length of the blocks and can be written as a product of a
power law and an exponential decay. It thereby interpolates between the
entanglement of individual spins and blocks of spins. It captures features of
correlation functions at criticality as well as the monogamous nature of
entanglement. We exemplify invariant features of this entanglement to
microscopic changes within the same universality class. We find this
entanglement to be invariant with respect to simultaneous scale transformations
of the separation and the length of the blocks. As a corollary, this study
estimates the entanglement between separated regions of those quantum fields to
which the considered spin models map at criticality.Comment: 4 pages, 3 figures; comments welcom
AER Neuro-Inspired interface to Anthropomorphic Robotic Hand
Address-Event-Representation (AER) is a
communication protocol for transferring asynchronous events
between VLSI chips, originally developed for neuro-inspired
processing systems (for example, image processing). Such
systems may consist of a complicated hierarchical structure
with many chips that transmit data among them in real time,
while performing some processing (for example, convolutions).
The information transmitted is a sequence of spikes coded using
high speed digital buses. These multi-layer and multi-chip AER
systems perform actually not only image processing, but also
audio processing, filtering, learning, locomotion, etc. This paper
present an AER interface for controlling an anthropomorphic
robotic hand with a neuro-inspired system.Unión Europea IST-2001-34124 (CAVIAR)Ministerio de Ciencia y Tecnología TIC-2003-08164-C03-02Ministerio de Ciencia y Tecnología TIC2000-0406-P4- 0
Fracton-elasticity duality on curved manifolds
Mechanical properties of crystals on curved substrates mix elastic, geometric
and topological degrees of freedom. In order to elucidate properties of such
crystals we formulate the low-energy effective action that combines metric
degrees of freedom with displacement fields and defects. We propose new
dualities for elasticity coupled to curved geometry formulated in terms of
tensor gauge theories. We show that the metric degrees of freedom, evolving
akin to linearized gravity are mapped to tensors with three indices. When
coupled to crystals these degrees of freedom become gapped and, in the presence
of dislocations and disclinations, multivalued. The elastic degrees of freedom
remain gapless and mapped to symmetric gauge fields with two indices. In the
dual formulation, topological defects, which act as sources for the gauge
fields, are fractons or excitations with restricted mobility. We show that
mobility restrictions are manifest only when singularities in both displacement
fields and metric are taken into account.Comment: 5 pages, 1 figur
Extraction of Pure Entangled States from Many Body Systems by Distant Local Projections
We study the feasibility of extracting a pure entangled state of
non-complementary, and potentially well separated, regions of a quantum
many-body system. It is shown that this can indeed be accomplished in
non-equilibrium scenarios as well as the ground state of the considered spin
chain models when one locally measures observables such as magnetization in
separated blocks of spins. A general procedure is presented, which can search
for the optimal way to extract a pure entangled state through local
projections. Our results indicate a connection of the projective extraction of
entanglement to good quantum numbers of the underlying Hamiltonian.Comment: 7 pages, 5 figures. Comments welcom
Emulación del sistema músculo-esqueletal y el control de movimiento en una plataforma experimental
Muchos fisiólogos han observado que el músculo
humano o animal es una especie de tejido elástico
(como un muelle) con componentes contráctiles,
los cuales dan una longitud de umbral modificable
neuralmente para el desarrollo de fuerzas.
La determinación de las fuerzas del músculo durante
el movimiento no es solamente esencial para
el análisis de las cargas internas que actúan en
los huesos y articulaciones, si no que también
contribuyen ha entender más profundamente los
controladores neuronales. Los sistemas de control
biológicos han sido estudiados como una posible
inspiración para la construción de controladores
de sistemas robóticos. En este trabajo,
se diseño e implemento un sistema biomecánico
que tiene propiedades mécanicas casi similares a
las de un brazo humano o animal. En este sistema
se implementaron modelos matemáticos del
músculo biológico, para la generación de fuerzas
en el músculo esqueletal total. Además, se desarrollo
una red cortical para el control de movimientos
voluntarios con restricciones neurofisiológicas
y psicofísicas motoras. El controlador neuronal
es propuesto para realizar el seguimiento de trajectorias
deseadas en la articulación de un simple
eslabón controlado por un par de actuadores
agonista-antagonista con propiedades musculares.
El sistema es capaz de ejecutar movimientos de
alcance voluntarios, con perfiles de velocidad en
forma de campana bajo perturbaciones. Los resultados
experimentales muestran que el sistema
presenta las propiedades básicas del músculoesqueletal
las cuales son las relaciones fuerza-longitud
y fuerza-velocidad. El controlador neuronal
permite controlar los movimientos deseados
y compesar las fuerzas externas.Se agradece el apoyo recibido por los miembros
del grupo de investigación de Neurotecnología,
Control y Robótica (NEUROCOR) del departamento
de Ingeniería de Sistemas y Automática de
la Universidad Politécnica de Cartagena. Este
trabajo fue financiado en parte por la CICYTTIC99-
0446-C02-01, y por el proyecto SYNERAGH
- BRE2-CT980797 BRITE EURAM- de
Investigación Básica
Holographic View on Quantum Correlations and Mutual Information between Disjoint Blocks of a Quantum Critical System
In (d+1) dimensional Multiscale Entanglement Renormalization Ansatz (MERA)
networks, tensors are connected so as to reproduce the discrete, (d + 2)
holographic geometry of Anti de Sitter space (AdSd+2) with the original system
lying at the boundary. We analyze the MERA renormalization flow that arises
when computing the quantum correlations between two disjoint blocks of a
quantum critical system, to show that the structure of the causal cones
characteristic of MERA, requires a transition between two different regimes
attainable by changing the ratio between the size and the separation of the two
disjoint blocks. We argue that this transition in the MERA causal developments
of the blocks may be easily accounted by an AdSd+2 black hole geometry when the
mutual information is computed using the Ryu-Takayanagi formula. As an explicit
example, we use a BTZ AdS3 black hole to compute the MI and the quantum
correlations between two disjoint intervals of a one dimensional boundary
critical system. Our results for this low dimensional system not only show the
existence of a phase transition emerging when the conformal four point ratio
reaches a critical value but also provide an intuitive entropic argument
accounting for the source of this instability. We discuss the robustness of
this transition when finite temperature and finite size effects are taken into
account.Comment: 21 pages, 5 figures. Abstract and Figure 1 has been modified. Minor
modifications in Section 1 and Section
Holographic Geometry of Entanglement Renormalization in Quantum Field Theories
We study a conjectured connection between the AdS/CFT and a real-space
quantum renormalization group scheme, the multi-scale entanglement
renormalization ansatz (MERA). By making a close contact with the holographic
formula of the entanglement entropy, we propose a general definition of the
metric in the MERA in the extra holographic direction, which is formulated
purely in terms of quantum field theoretical data. Using the continuum version
of the MERA (cMERA), we calculate this emergent holographic metric explicitly
for free scalar boson and free fermions theories, and check that the metric so
computed has the properties expected from AdS/CFT. We also discuss the cMERA in
a time-dependent background induced by quantum quench and estimate its
corresponding metric.Comment: 42pages, 9figures, reference added, minor chang
Boundary States as Holographic Duals of Trivial Spacetimes
We study real-space quantum entanglement included in conformally invariant
boundary states in conformal field theories (CFTs). First, we argue that
boundary states essentially have no real-space entanglement by computing the
entanglement entropy when we bipartite the system into two spatial regions.
From the viewpoint of holography, this shows that boundary states are dual to
trivial spacetimes of zero spactime volume. Next, we point out that a
continuous multiscale entanglement renormalization ansatz (cMERA) for any CFTs
can be formulated by employing a boundary state as its infrared unentangled
state with an appropriate regularization. Exploiting this idea, we propose an
approximation scheme of cMERA construction for general CFTs.Comment: 30 pages, 4 figure
Entanglement Entropy from a Holographic Viewpoint
The entanglement entropy has been historically studied by many authors in
order to obtain quantum mechanical interpretations of the gravitational
entropy. The discovery of AdS/CFT correspondence leads to the idea of
holographic entanglement entropy, which is a clear solution to this important
problem in gravity. In this article, we would like to give a quick survey of
recent progresses on the holographic entanglement entropy. We focus on its
gravitational aspects, so that it is comprehensible to those who are familiar
with general relativity and basics of quantum field theory.Comment: Latex, 30 pages, invited review for Classical and Quantum Gravity,
minor correction
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