850 research outputs found
Reply to Comment on "A local realist model for correlations of the singlet state"
The general conclusion of Seevinck and Larsson is that our model exploits the
so-called coincidence-time loophole and produces sinusoidal (quantum-like)
correlations but does not model the singlet state because it does not violate
the relevant Bell inequality derived by Larsson and Gill, since in order to
obtain the sinusoidal correlations the probability of coincidences in our model
goes to zero. In this reply, we refute their arguments that lead to this
conclusion and demonstrate that our model can reproduce results of photon and
ion-trap experiments with frequencies of coincidences that are not in conflict
with the observations.Comment: Corrected typo
Efficient data processing and quantum phenomena: Single-particle systems
We study the relation between the acquisition and analysis of data and
quantum theory using a probabilistic and deterministic model for photon
polarizers. We introduce criteria for efficient processing of data and then use
these criteria to demonstrate that efficient processing of the data contained
in single events is equivalent to the observation that Malus' law holds. A
strictly deterministic process that also yields Malus' law is analyzed in
detail. We present a performance analysis of the probabilistic and
deterministic model of the photon polarizer. The latter is an adaptive
dynamical system that has primitive learning capabilities. This additional
feature has recently been shown to be sufficient to perform event-by-event
simulations of interference phenomena, without using concepts of wave
mechanics. We illustrate this by presenting results for a system of two chained
Mach-Zehnder interferometers, suggesting that systems that perform efficient
data processing and have learning capability are able to exhibit behavior that
is usually attributed to quantum systems only.Comment: http://www.compphys.net/dl
Deceptive Apparent Nonadiabatic Magnetization Process
We discuss the effect of the thermal environment on the low-temperature
response of the magnetization of uniaxial magnets to a time-dependent applied
magnetic field. At sufficiently low temperatures the staircase magnetization
curves observed in molecular magnets such as Mn_{12} and Fe_8 display little
temperature dependence. However the changes of the magnetization at each step
do not seem to be directly related to the probability for a quantum mechanical
nonadiabatic transition. In order to explain this deceptive apparent
nonadiabatic behavior, we study the quantum dynamics of the system in a thermal
environment and propose a relation between the observed magnetization steps and
the quantum mechanical transition probability due to the nonadiabatic
transition.Comment: 4 pages, 7 eps figure
Put on your poker face? Neural systems supporting the anticipation for expressive suppression and cognitive reappraisal
It is a unique human ability to regulate negative thoughts and feelings. Two well-investigated emotion-regulation strategies (ERSs), cognitive reappraisal and expressive suppression, are associated with overlapping prefrontal neural correlates, but differ temporally during the emotion-generation process. Although functional imaging studies have mainly investigated these ERS as a reaction to an emotion-inducing event, the intention to regulate upcoming negative emotions might already be associated with differences in neural activity. Hence, event-related functional magnetic resonance imaging was recorded in 42 participants while they completed an emotion-regulation paradigm. During this task, participants were instructed to proactively prepare to use a specific ERS knowing that a negative, high-arousing image would appear after the preparation period. As expected, the results demonstrated prefrontal and parietal activation while participants were suppressing or reappraising their emotions (family-wise error (FWE)-corrected). The intention to suppress emotions was associated with increased activation in the right inferior frontal gyrus, bilateral putamen, pre-supplementary motor area and right supramarginal gyrus (FWE-corrected). This enhanced proactive inhibitory control: (i) predicted decreased motoric activity during the actual suppression of emotional expressions and (2) trended toward a significant association with how successfully participants suppressed their emotions. However, neural correlates of preparatory control for cognitive reappraisal were not observed, possibly because contextual cues about the upcoming emotional stimulus are necessary to proactively start to cognitively reinterpret the situation
Morphological Image Analysis of Quantum Motion in Billiards
Morphological image analysis is applied to the time evolution of the
probability distribution of a quantum particle moving in two and
three-dimensional billiards. It is shown that the time-averaged Euler
characteristic of the probability density provides a well defined quantity to
distinguish between classically integrable and non-integrable billiards. In
three dimensions the time-averaged mean breadth of the probability density may
also be used for this purpose.Comment: Major revision. Changes include a more detailed discussion of the
theory and results for 3 dimensions. Now: 10 pages, 9 figures (some are
colored), 3 table
Computer simulation of Wheeler's delayed choice experiment with photons
We present a computer simulation model of Wheeler's delayed choice experiment
that is a one-to-one copy of an experiment reported recently (V. Jacques {\sl
et al.}, Science 315, 966 (2007)). The model is solely based on experimental
facts, satisfies Einstein's criterion of local causality and does not rely on
any concept of quantum theory. Nevertheless, the simulation model reproduces
the averages as obtained from the quantum theoretical description of Wheeler's
delayed choice experiment. Our results prove that it is possible to give a
particle-only description of Wheeler's delayed choice experiment which
reproduces the averages calculated from quantum theory and which does not defy
common sense.Comment: Europhysics Letters (in press
Number Partitioning on a Quantum Computer
We present an algorithm to compute the number of solutions of the
(constrained) number partitioning problem. A concrete implementation of the
algorithm on an Ising-type quantum computer is given.Comment: 5 pages, 1 figure, see also
http://rugth30.phys.rug.nl/compphys/qce.ht
Fast Algorithm for Finding the Eigenvalue Distribution of Very Large Matrices
A theoretical analysis is given of the equation of motion method, due to
Alben et al., to compute the eigenvalue distribution (density of states) of
very large matrices. The salient feature of this method is that for matrices of
the kind encountered in quantum physics the memory and CPU requirements of this
method scale linearly with the dimension of the matrix. We derive a rigorous
estimate of the statistical error, supporting earlier observations that the
computational efficiency of this approach increases with matrix size. We use
this method and an imaginary-time version of it to compute the energy and the
specific heat of three different, exactly solvable, spin-1/2 models and compare
with the exact results to study the dependence of the statistical errors on
sample and matrix size.Comment: 24 pages, 24 figure
Beyond the poor man's implementation of unconditionally stable algorithms to solve the time-dependent Maxwell Equations
For the recently introduced algorithms to solve the time-dependent Maxwell
equations (see Phys.Rev.E Vol.64 p.066705 (2001)), we construct a variable grid
implementation and an improved spatial discretization implementation that
preserve the property of the algorithms to be unconditionally stable by
construction. We find that the performance and accuracy of the corresponding
algorithms are significant and illustrate their practical relevance by
simulating various physical model systems.Comment: 18 pages, 16 figure
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