536 research outputs found
Tailoring optical fields emitted by nanometric sources
Here we study a simple way of controlling the emitted fields of
sub-wavelength nanometric sources. The system consists of arrays of
nanoparticles (NPs) embedded in optical active media. The key concept is the
careful tuning of NP's damping factors, which changes the eigenmode's decay
rates of the whole array. This, at long time, leads to a locking of relative
phases and frequencies of individual localized-surfaces-plasmons (LSPs) and,
thus, controlls the emitted field. The amplitude of the LSP's oscillations can
be kept constant by embedding the system in optical active media. In the case
of full loss compensation, this implies that, not only the relative phases, but
also the amplitudes of the LSPs remain fixed, leading us, additionally, to
interpret the process as a new example of synchronization. The proposed
approach can be used as a general way of controlling and designing the
electromagnetic fields emitted by nanometric sources, which can find
applications in optoelectronic, nanoscale lithography and probing microscopy
Boxing the face: A comparison of dynamic facial databases used in facial analysis and animation.
Child Witnesses and the Confrontation Clause
After the Supreme Court’s ruling in Crawford v. Washington that a criminal defendant’s right to confront the witnesses against him is violated by the admission of testimonial hearsay that has not been cross-examined, lower courts have overturned convictions in which hearsay from children was admitted after child witnesses were either unwilling or unable to testify. A review of social scientific evidence regarding the dynamics of child sexual abuse suggests a means for facilitating the fair receipt of children’s evidence. Courts should hold that defendants have forfeited their confrontation rights if they exploited a child’s vulnerabilities such that they could reasonably anticipate that the child would be unavailable to testify. Exploitation includes choosing victims on the basis of their filial dependency, their vulnerability, or their immaturity, as well as taking actions that create or accentuate those vulnerabilities
Measures and metrics for automatic emotion classification via FACET
For dynamic emotions to be modelled in a natural and
convincing way, systems must rely on accurate affective analysis
of facial expressions in the first place. The present work
introduces two measures for evaluating automatic emotion
classification performance. It further provides a systematic
comparison between 14 databases of dynamic expressions.
Machine analysis was conducted using the FACET system, with
an algorithm calculating recognition sensitivity and confidence.
Results revealed the proportion of facial stimuli that could be
recognised by the machine algorithm above threshold evidence,
showing significant differences in recognition performance
between the databases
The Loschmidt Echo as a robust decoherence quantifier for many-body systems
We employ the Loschmidt Echo, i.e. the signal recovered after the reversal of
an evolution, to identify and quantify the processes contributing to
decoherence. This procedure, which has been extensively used in single particle
physics, is here employed in a spin ladder. The isolated chains have 1/2 spins
with XY interaction and their excitations would sustain a one-body like
propagation. One of them constitutes the controlled system S whose reversible
dynamics is degraded by the weak coupling with the uncontrolled second chain,
i.e. the environment E. The perturbative SE coupling is swept through arbitrary
combinations of XY and Ising like interactions, that contain the standard
Heisenberg and dipolar ones. Different time regimes are identified for the
Loschmidt Echo dynamics in this perturbative configuration. In particular, the
exponential decay scales as a Fermi golden rule, where the contributions of the
different SE terms are individually evaluated and analyzed. Comparisons with
previous analytical and numerical evaluations of decoherence based on the
attenuation of specific interferences, show that the Loschmidt Echo is an
advantageous decoherence quantifier at any time, regardless of the S internal
dynamics.Comment: 12 pages, 6 figure
Boosting quantum evolutions using Trotter-Suzuki algorithms on GPUs
The evolution calculation of quantum systems represents a great challenge nowadays. Numerical implementations typically scale exponentially with the size of the system, demanding high amounts of resources. General Purpose Graphics Processor Units (GPGPUs) enable a new range of possibilities for numerical simulations of quantum systems. In this work we implemented, optimized and compared the quantum Trotter-Suzuki algorithm running on both CPUs and GPUs.Sociedad Argentina de Informática e Investigación Operativ
Non-Markovian decay and dynamics of decoherence in private and public environments
We study the decay process in an open system, emphasizing on the relevance of
the environment's spectral structure. Non-Markovian effects are included to
quantitatively analyze the degradation rate of the coherent evolution. The way
in which a two level system is coupled to different environments is
specifically addressed: multiple connections to a single bath (public
environment)or single connections to multiple baths (private environments). We
numerically evaluate the decay rate of a local excitation by using the Survival
Probability and the Loschmidt Echo. These rates are compared to analytical
results obtained from the standard Fermi Golden Rule (FGR) in Wide Band
Approximation, and a Self-Consistent evaluation that accounts for the bath's
memory in cases where an exact analytical solution is possible. We observe that
the correlations appearing in a public bath introduce further deviations from
the FGR as compared with a private bath.Comment: 18 pages, 7 figures. Accepted for publication in Physical Review
Experimental quantification of decoherence via the Loschmidt echo in a many spin system with scaled dipolar Hamiltonians
We performed Loschmidt echo nuclear magnetic resonance experiments to study decoherence under a scaled dipolar Hamiltonian by means of a symmetrical time-reversal pulse sequence denominated Proportionally Refocused Loschmidt (PRL) echo. The many-spin system represented by the protons in polycristalline adamantane evolves through two steps of evolution characterized by the secular part of the dipolar Hamiltonian, scaled down with a factor |k| and opposite signs. The scaling factor can be varied continuously from 0 to 1/2, giving access to a range of complexity in the dynamics. The experimental results for the Loschmidt echoes showed a spreading of the decay rates that correlate directly to the scaling factors |k|, giving evidence that the decoherence is partially governed by the coherent dynamics. The average Hamiltonian theory was applied to give an insight into the spin dynamics during the pulse sequence. The calculations were performed for every single radio frequency block in contrast to the most widely used form. The first order of the average Hamiltonian numerically computed for an 8-spin system showed decay rates that progressively decrease as the secular dipolar Hamiltonian becomes weaker. Notably, the first order Hamiltonian term neglected by conventional calculations yielded an explanation for the ordering of the experimental decoherence rates. However, there is a strong overall decoherence observed in the experiments which is not reflected by the theoretical results. The fact that the non-inverted terms do not account for this effect is a challenging topic. A number of experiments to further explore the relation of the complete Hamiltonian with this dominant decoherence rate are proposed.publishedVersionFil: Buljubasich, Lisandro. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Sánchez, Claudia M. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Dente, Axel D. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Levstein, Patricia R. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Chattah, Ana K. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Pastawski, Horacio M. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Buljubasich, Lisandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Dente, Axel D. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Levstein, Patricia R. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Chattah, Ana K. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Pastawski, Horacio M. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Física Atómica, Molecular y Química (física de átomos y moléculas incluyendo colisión, interacción con radiación, resonancia magnética, Moessbauer Efecto.
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