831 research outputs found
Computer generation of human gait kinematics
The paper describes a computer program that generates absolute motion variables of human gait from predetermined relative motions. Relative displacements are measured over a range of step rates during both free (self-determined step rate at different speeds) and forced (forced step rate at a constant speed) walking, converted into harmonic coefficients and stored in an array as a function of step rate. Only six variable identifiers need to be specified to compute any absolute variable or its derivatives at any desirable step rate. The paper displays some examples of measured relative motions and reconstituted absolute variables.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23673/1/0000641.pd
Spin squeezing, entanglement and quantum metrology with Bose-Einstein condensates
Squeezed states, a special kind of entangled states, are known as a useful
resource for quantum metrology. In interferometric sensors they allow to
overcome the "classical" projection noise limit stemming from the independent
nature of the individual photons or atoms within the interferometer. Motivated
by the potential impact on metrology as wells as by fundamental questions in
the context of entanglement, a lot of theoretical and experimental effort has
been made to study squeezed states. The first squeezed states useful for
quantum enhanced metrology have been proposed and generated in quantum optics,
where the squeezed variables are the coherences of the light field. In this
tutorial we focus on spin squeezing in atomic systems. We give an introduction
to its concepts and discuss its generation in Bose-Einstein condensates. We
discuss in detail the experimental requirements necessary for the generation
and direct detection of coherent spin squeezing. Two exemplary experiments
demonstrating adiabatically prepared spin squeezing based on motional degrees
of freedom and diabatically realized spin squeezing based on internal hyperfine
degrees of freedom are discussed.Comment: Phd tutorial, 23 pages, 17 figure
f-Oscillators and Nonlinear Coherent States
The notion of f-oscillators generalizing q-oscillators is introduced. For
classical and quantum cases, an interpretation of the f-oscillator is provided
as corresponding to a special nonlinearity of vibration for which the frequency
of oscillation depends on the energy. The f-coherent states (nonlinear coherent
states) generalizing q-coherent states are constructed. Applied to quantum
optics, photon distribution function, photon number means, and dispersions are
calculated for the f-coherent states as well as the Wigner function and
Q-function. As an example, it is shown how this nonlinearity may affect the
Planck distribution formula.Comment: Latex, 32 pages, accepted by Physica Script
Education and older adults at the University of the Third Age
This article reports a critical analysis of older adult education in Malta. In educational gerontology, a critical perspective demands the exposure of how relations of power and inequality, in their myriad forms, combinations, and complexities, are manifest in late-life learning initiatives. Fieldwork conducted at the University of the Third Age (UTA) in Malta uncovered the political nature of elder-learning, especially with respect to three intersecting lines of inequality - namely, positive aging, elitism, and gender. A cautionary note is, therefore, warranted at the dominant positive interpretations of UTAs since late-life learning, as any other education activity, is not politically neutral.peer-reviewe
Wehrl entropy, Lieb conjecture and entanglement monotones
We propose to quantify the entanglement of pure states of
bipartite quantum system by defining its Husimi distribution with respect to
coherent states. The Wehrl entropy is minimal if and only
if the pure state analyzed is separable. The excess of the Wehrl entropy is
shown to be equal to the subentropy of the mixed state obtained by partial
trace of the bipartite pure state. This quantity, as well as the generalized
(R{\'e}nyi) subentropies, are proved to be Schur--convex, so they are
entanglement monotones and may be used as alternative measures of entanglement
Geometric approach to nonlinear coherent states using the Higgs model for harmonic oscillator
In this paper, we investigate the relation between the curvature of the
physical space and the deformation function of the deformed oscillator algebra
using non-linear coherent states approach. For this purpose, we study
two-dimensional harmonic oscillators on the flat surface and on a sphere by
applying the Higgs modell. With the use of their algebras, we show that the
two-dimensional oscillator algebra on a surface can be considered as a deformed
one-dimensional oscillator algebra where the effect of the curvature of the
surface is appeared as a deformation function. We also show that the curvature
of the physical space plays the role of deformation parameter. Then we
construct the associated coherent states on the flat surface and on a sphere
and compare their quantum statistical properties, including quadrature
squeezing and antibunching effect.Comment: 12 pages, 7 figs. To be appeared in J. Phys.
Entanglement capability of self-inverse Hamiltonian evolution
We determine the entanglement capability of self-inverse Hamiltonian
evolution, which reduces to the known result for Ising Hamiltonian, and
identify optimal input states for yielding the maximal entanglement rate. We
introduce the concept of the operator entanglement rate, and find that the
maximal operator entanglement rate gives a lower bound on the entanglement
capability of a general Hamiltonian.Comment: 4 pages, no figures. Version 3: small change
Quantum learning: optimal classification of qubit states
Pattern recognition is a central topic in Learning Theory with numerous
applications such as voice and text recognition, image analysis, computer
diagnosis. The statistical set-up in classification is the following: we are
given an i.i.d. training set where
represents a feature and is a label attached to that
feature. The underlying joint distribution of is unknown, but we can
learn about it from the training set and we aim at devising low error
classifiers used to predict the label of new incoming features.
Here we solve a quantum analogue of this problem, namely the classification
of two arbitrary unknown qubit states. Given a number of `training' copies from
each of the states, we would like to `learn' about them by performing a
measurement on the training set. The outcome is then used to design mesurements
for the classification of future systems with unknown labels. We find the
asymptotically optimal classification strategy and show that typically, it
performs strictly better than a plug-in strategy based on state estimation.
The figure of merit is the excess risk which is the difference between the
probability of error and the probability of error of the optimal measurement
when the states are known, that is the Helstrom measurement. We show that the
excess risk has rate and compute the exact constant of the rate.Comment: 24 pages, 4 figure
The Utility of Video Diaries for Organizational Research
This article assesses the utility of video diaries as a method for organization studies. While it is frequently suggested that video-based research methodologies have the capacity to capture new data about the minutiae of complex organizational affairs, as well as offering new forms of dissemination to both academic and professional audiences, little is known about the specific benefits and drawbacks of video diaries. We compare video diaries with two established and “adjacent” methods: traditional diary studies (written or audio) and other video methods. We evaluate each in relation to three key research areas: bodily expressions, identity, and practice studies. Our assessment of video diaries suggests that the approach is best used as a complement to other forms of research and is particularly suited to capturing plurivocal, asynchronous accounts of organizational phenomena. We use illustrations from an empirical research project to exemplify our claims before concluding with five points of advice for researchers wishing to employ this method
Renyi-Wehrl entropies as measures of localization in phase space
We generalize the concept of the Wehrl entropy of quantum states which gives
a basis-independent measure of their localization in phase space. We discuss
the minimal values and the typical values of these R{enyi-Wehrl entropies for
pure states for spin systems. According to Lieb's conjecture the minimal values
are provided by the spin coherent states. Though Lieb's conjecture remains
unproven, we give new proofs of partial results that may be generalized for
other systems. We also investigate random pure states and calculate the mean
Renyi-Wehrl entropies averaged over the natural measure in the space of pure
quantum states.Comment: 18 pages, no figures, some improved versions of main proofs, added
J.referenc
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