462 research outputs found
A Quantum-Bayesian Route to Quantum-State Space
In the quantum-Bayesian approach to quantum foundations, a quantum state is
viewed as an expression of an agent's personalist Bayesian degrees of belief,
or probabilities, concerning the results of measurements. These probabilities
obey the usual probability rules as required by Dutch-book coherence, but
quantum mechanics imposes additional constraints upon them. In this paper, we
explore the question of deriving the structure of quantum-state space from a
set of assumptions in the spirit of quantum Bayesianism. The starting point is
the representation of quantum states induced by a symmetric informationally
complete measurement or SIC. In this representation, the Born rule takes the
form of a particularly simple modification of the law of total probability. We
show how to derive key features of quantum-state space from (i) the requirement
that the Born rule arises as a simple modification of the law of total
probability and (ii) a limited number of additional assumptions of a strong
Bayesian flavor.Comment: 7 pages, 1 figure, to appear in Foundations of Physics; this is a
condensation of the argument in arXiv:0906.2187v1 [quant-ph], with special
attention paid to making all assumptions explici
TIME-VARIANT SPECTRAL ANALYSIS OF SURFACE EMG SIGNALS – EXEMPLARILY SHOWN FOR ARCHERY
To analyse the spectral density of electromyographic (EMG) signals Fourier transforms are commonly used. The prerequisite of this transform is that the analysed signal is stationary. Generally, this can not be assumed for the electromyograms of muscle contractions of human movement. A new method to analyse non-stationary biological signals is the time-variant spectral analysis. The aim of this paper is to use the timevariant spectral analysis in a realistic sport application to show connections of the athlete’s level and the spectral density of the EMG. Five top-level archers participated in the study. The results suggest, that a higher level of performance generally corresponds to lower median-frequencies and a smaller variability of the median-frequencies of the EMG-signals
Competitive tenders on analogue hospital pharmaceuticals in Denmark 2017-2020
BACKGROUND: Competitive tenders on pharmaceuticals are one of the most effective cost-containment instruments in healthcare systems. Its effectiveness has been demonstrated, among other things, in markets for generic medicine and biosimilars. In Denmark, an internationally unique model for competitive tenders on analogue substitutable pharmaceuticals has been developed and implemented for all public hospitals. METHODS: We obtained data on all analogue competitive tenders carried out by the Danish Medicines Council from its foundation on January 1, 2017, to October 9, 2020. We calculated univariate descriptive statistics, pairwise correlations and made a multiple regression analysis on tender savings. RESULTS: Average annual saving on hospital pharmaceutical purchase prices was 44.1% ranging from 0.4% to 92.8% between therapeutic areas and areas of indication. There was a significant positive correlation between tender savings and the number of competitors participating in the tender, and a significant negative correlation between tender savings and the number of days since market authorization. CONCLUSIONS: This study finds analogue tenders to be similar in effect and mechanism to competitive tenders in markets for generic medicine and biosimilars. It supports the increasing number of empirical findings that competitive tendering has a high potential to generate substantial savings on healthcare budgets
Respecting One's Fellow: QBism's Analysis of Wigner's Friend
According to QBism, quantum states, unitary evolutions, and measurement
operators are all understood as personal judgments of the agent using the
formalism. Meanwhile, quantum measurement outcomes are understood as the
personal experiences of the same agent. Wigner's conundrum of the friend, in
which two agents ostensibly have different accounts of whether or not there is
a measurement outcome, thus poses no paradox for QBism. Indeed the resolution
of Wigner's original thought experiment was central to the development of QBist
thinking. The focus of this paper concerns two very instructive modifications
to Wigner's puzzle: One, a recent no-go theorem by Frauchiger and Renner, and
the other a thought experiment by Baumann and Brukner. We show that the
paradoxical features emphasized in these works disappear once both friend and
Wigner are understood as agents on an equal footing with regard to their
individual uses of quantum theory. Wigner's action on his friend then becomes,
from the friend's perspective, an action the friend takes on Wigner. Our
analysis rests on a kind of quantum Copernican principle: When two agents take
actions on each other, each agent has a dual role as a physical system for the
other agent. No user of quantum theory is more privileged than any other. In
contrast to the sentiment of Wigner's original paper, neither agent should be
considered as in "suspended animation." In this light, QBism brings an entirely
new perspective to understanding Wigner's friend thought experiments.Comment: 15 pages, 1 figur
Followup Study of Oklahoma Vocational and Nonvocational Students Nine Years after Graduation
Higher Educatio
Experimental Polarization State Tomography using Optimal Polarimeters
We report on the experimental implementation of a polarimeter based on a
scheme known to be optimal for obtaining the polarization vector of ensembles
of spin-1/2 quantum systems, and the alignment procedure for this polarimeter
is discussed. We also show how to use this polarimeter to estimate the
polarization state for identically prepared ensembles of single photons and
photon pairs and extend the method to obtain the density matrix for generic
multi-photon states. State reconstruction and performance of the polarimeter is
illustrated by actual measurements on identically prepared ensembles of single
photons and polarization entangled photon pairs
Chaos for Liouville probability densities
Using the method of symbolic dynamics, we show that a large class of
classical chaotic maps exhibit exponential hypersensitivity to perturbation,
i.e., a rapid increase with time of the information needed to describe the
perturbed time evolution of the Liouville density, the information attaining
values that are exponentially larger than the entropy increase that results
from averaging over the perturbation. The exponential rate of growth of the
ratio of information to entropy is given by the Kolmogorov-Sinai entropy of the
map. These findings generalize and extend results obtained for the baker's map
[R. Schack and C. M. Caves, Phys. Rev. Lett. 69, 3413 (1992)].Comment: 26 pages in REVTEX, no figures, submitted to Phys. Rev.
Quantum computers in phase space
We represent both the states and the evolution of a quantum computer in phase
space using the discrete Wigner function. We study properties of the phase
space representation of quantum algorithms: apart from analyzing important
examples, such as the Fourier Transform and Grover's search, we examine the
conditions for the existence of a direct correspondence between quantum and
classical evolutions in phase space. Finally, we describe how to directly
measure the Wigner function in a given phase space point by means of a
tomographic method that, itself, can be interpreted as a simple quantum
algorithm.Comment: 16 pages, 7 figures, to appear in Phys Rev
Realistic simulations of single-spin nondemolition measurement by magnetic resonance force microscopy
A requirement for many quantum computation schemes is the ability to measure
single spins. This paper examines one proposed scheme: magnetic resonance force
microscopy, including the effects of thermal noise and back-action from
monitoring. We derive a simplified equation using the adiabatic approximation,
and produce a stochastic pure state unraveling which is useful for numerical
simulations.Comment: 33 pages LaTeX, 9 figure files in EPS format. Submitted to Physical
Review
Qubit-Qutrit Separability-Probability Ratios
Paralleling our recent computationally-intensive (quasi-Monte Carlo) work for
the case N=4 (quant-ph/0308037), we undertake the task for N=6 of computing to
high numerical accuracy, the formulas of Sommers and Zyczkowski
(quant-ph/0304041) for the (N^2-1)-dimensional volume and (N^2-2)-dimensional
hyperarea of the (separable and nonseparable) N x N density matrices, based on
the Bures (minimal monotone) metric -- and also their analogous formulas
(quant-ph/0302197) for the (non-monotone) Hilbert-Schmidt metric. With the same
seven billion well-distributed (``low-discrepancy'') sample points, we estimate
the unknown volumes and hyperareas based on five additional (monotone) metrics
of interest, including the Kubo-Mori and Wigner-Yanase. Further, we estimate
all of these seven volume and seven hyperarea (unknown) quantities when
restricted to the separable density matrices. The ratios of separable volumes
(hyperareas) to separable plus nonseparable volumes (hyperareas) yield
estimates of the separability probabilities of generically rank-six (rank-five)
density matrices. The (rank-six) separability probabilities obtained based on
the 35-dimensional volumes appear to be -- independently of the metric (each of
the seven inducing Haar measure) employed -- twice as large as those (rank-five
ones) based on the 34-dimensional hyperareas. Accepting such a relationship, we
fit exact formulas to the estimates of the Bures and Hilbert-Schmidt separable
volumes and hyperareas.(An additional estimate -- 33.9982 -- of the ratio of
the rank-6 Hilbert-Schmidt separability probability to the rank-4 one is quite
clearly close to integral too.) The doubling relationship also appears to hold
for the N=4 case for the Hilbert-Schmidt metric, but not the others. We fit
exact formulas for the Hilbert-Schmidt separable volumes and hyperareas.Comment: 36 pages, 15 figures, 11 tables, final PRA version, new last
paragraph presenting qubit-qutrit probability ratios disaggregated by the two
distinct forms of partial transpositio
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