330 research outputs found
Semi-device-independent bounds on entanglement
Detection and quantification of entanglement in quantum resources are two key
steps in the implementation of various quantum-information processing tasks.
Here, we show that Bell-type inequalities are not only useful in verifying the
presence of entanglement but can also be used to bound the entanglement of the
underlying physical system. Our main tool consists of a family of
Clauser-Horne-like Bell inequalities that cannot be violated maximally by any
finite-dimensional maximally entangled state. Using these inequalities, we
demonstrate the explicit construction of both lower and upper bounds on the
concurrence for two-qubit states. The fact that these bounds arise from
Bell-type inequalities also allows them to be obtained in a
semi-device-independent manner, that is, with assumption of the dimension of
the Hilbert space but without resorting to any knowledge of the actual
measurements being performed on the individual subsystems.Comment: 8 pages, 2 figures (published version). Note 1: Title changed to
distinguish our approach from the standard device-independent scenario where
no assumption on the Hilbert space dimension is made. Note 2: This paper
contains explicit examples of more nonlocality with less entanglement in the
simplest CH-like scenario (see also arXiv:1011.5206 by Vidick and Wehner for
related results
Multifactorial QT interval prolongation
Acquired long QT interval has been widely reported to be a consequence of drug therapy and
electrolyte disturbances. We describe two cases of multifactorial acquired QT interval prolongation
and torsades de pointes. In the first case, the drugs venlafaxine, amiodarone and
domperidone may have contributed to QT interval prolongation in a patient with hypokalemia
and hypomagnesaemia. In the second case, QT interval prolongation occurred in a patient
taking quetiapine and citalopram, and whose use of hydrocholorothiazide and history of chronic
alcohol abuse likely contributed by rendering the patient hypokalemic. These cases highlight the
potential risks associated with polypharmacy and demonstrate that though torsades de pointes
is an uncommon arrhythmia, the combination of multiple factors known to prolong
QT interval may precipitate this life-threatening arrhythmia. (Cardiol J 2010; 17, 2: 184-188
Nonlocality and entanglement in a strange system
We show that the relation between nonlocality and entanglement is subtler
than one naively expects. In order to do this we consider the neutral kaon
system--which is oscillating in time (particle--antiparticle mixing) and
decaying--and describe it as an open quantum system. We consider a Bell--CHSH
inequality and show a novel violation for non--maximally entangled states.
Considering the change of purity and entanglement in time we find that, despite
the fact that only two degrees of freedom at a certain time can be measured,
the neutral kaon system does not behave like a bipartite qubit system.Comment: 7 pages, 2 figures, extended versio
Quantum networks reveal quantum nonlocality
The results of local measurements on some composite quantum systems cannot be
reproduced classically. This impossibility, known as quantum nonlocality,
represents a milestone in the foundations of quantum theory. Quantum
nonlocality is also a valuable resource for information processing tasks, e.g.
quantum communication, quantum key distribution, quantum state estimation, or
randomness extraction. Still, deciding if a quantum state is nonlocal remains a
challenging problem. Here we introduce a novel approach to this question: we
study the nonlocal properties of quantum states when distributed and measured
in networks. Using our framework, we show how any one-way entanglement
distillable state leads to nonlocal correlations. Then, we prove that
nonlocality is a non-additive resource, which can be activated. There exist
states, local at the single-copy level, that become nonlocal when taking
several copies of it. Our results imply that the nonlocality of quantum states
strongly depends on the measurement context.Comment: 4 + 3 pages, 4 figure
Analytical method for parameterizing the random profile components of nanosurfaces imaged by atomic force microscopy
The functional properties of many technological surfaces in biotechnology,
electronics, and mechanical engineering depend to a large degree on the
individual features of their nanoscale surface texture, which in turn are a
function of the surface manufacturing process. Among these features, the
surface irregularities and self-similarity structures at different spatial
scales, especially in the range of 1 to 100 nm, are of high importance because
they greatly affect the surface interaction forces acting at a nanoscale
distance. An analytical method for parameterizing the surface irregularities
and their correlations in nanosurfaces imaged by atomic force microscopy (AFM)
is proposed. In this method, flicker noise spectroscopy - a statistical physics
approach - is used to develop six nanometrological parameters characterizing
the high-frequency contributions of jump- and spike-like irregularities into
the surface texture. These contributions reflect the stochastic processes of
anomalous diffusion and inertial effects, respectively, in the process of
surface manufacturing. The AFM images of the texture of corrosion-resistant
magnetite coatings formed on low-carbon steel in hot nitrate solutions with
coating growth promoters at different temperatures are analyzed. It is shown
that the parameters characterizing surface spikiness are able to quantify the
effect of process temperature on the corrosion resistance of the coatings. It
is suggested that these parameters can be used for predicting and
characterizing the corrosion-resistant properties of magnetite coatings.Comment: 7 pages, 3 figures, 2 tables; to be published in Analys
Dynamic Interpretation of Hedgehog Signaling in the Drosophila Wing Disc
Morphogens are classically defined as molecules that control patterning by acting at a distance to regulate gene expression in a concentration-dependent manner. In the Drosophila wing imaginal disc, secreted Hedgehog (Hh) forms an extracellular gradient that organizes patterning along the anterior–posterior axis and specifies at least three different domains of gene expression. Although the prevailing view is that Hh functions in the Drosophila wing disc as a classical morphogen, a direct correspondence between the borders of these patterns and Hh concentration thresholds has not been demonstrated. Here, we provide evidence that the interpretation of Hh signaling depends on the history of exposure to Hh and propose that a single concentration threshold is sufficient to support multiple outputs. Using mathematical modeling, we predict that at steady state, only two domains can be defined in response to Hh, suggesting that the boundaries of two or more gene expression patterns cannot be specified by a static Hh gradient. Computer simulations suggest that a spatial “overshoot” of the Hh gradient occurs, i.e., a transient state in which the Hh profile is expanded compared to the Hh steady-state gradient. Through a temporal examination of Hh target gene expression, we observe that the patterns initially expand anteriorly and then refine, providing in vivo evidence for the overshoot. The Hh gene network architecture suggests this overshoot results from the Hh-dependent up-regulation of the receptor, Patched (Ptc). In fact, when the network structure was altered such that the ptc gene is no longer up-regulated in response to Hh-signaling activation, we found that the patterns of gene expression, which have distinct borders in wild-type discs, now overlap. Our results support a model in which Hh gradient dynamics, resulting from Ptc up-regulation, play an instructional role in the establishment of patterns of gene expression
Assessing changes to adolescent health-promoting behaviors following the onset of the COVID-19 pandemic: A multi-methods exploration of the role of within-person combinations of trait perfectionism.
The current work provides a multi-methods exploration of how within-person subtypes of self-oriented perfectionism (SOP) and socially prescribed perfectionism (SPP) were related to shifts in health-promoting behaviors among adolescents following the onset of the COVID-19 pandemic. Study One tested the 2 × 2 and tripartite models of perfectionism through a quantitative test of how such subtypes predicted changes in health behaviors pre-pandemic to intra-pandemic among 202 adolescents (M = 17.86, SD = 1.421). Results indicated that the combination of high SOP/high SPP was linked to the most maladaptive changes to health-promoting behaviors, supporting the tripartite model. Study Two aimed to contextualize these findings by analyzing semi-structured interviews with 31 adolescent self-identified perfectionists (M = 15.97, SD = 1.991) during the initial lockdown mandate. Results indicated that participants experienced a welcome break and found more time to engage in health-promoting behaviors. However, those high in SOP - regardless of their level of SPP - had more difficulty relaxing due to a resistance to relenting their perfectionistic standards. Altogether, these findings support the exacerbating role of SOP when combined with SPP posited by the tripartite model of perfectionism with respect to adolescents' health-promoting behaviors during the COVID-19 pandemic.This work was supported by an Ontario Government Early Researcher Award awarded to Danielle S. Molnar (Ministry of Research and Innovation, Government of Ontario)
Large violation of Bell inequalities with low entanglement
In this paper we obtain violations of general bipartite Bell inequalities of
order with inputs, outputs and
-dimensional Hilbert spaces. Moreover, we construct explicitly, up to a
random choice of signs, all the elements involved in such violations: the
coefficients of the Bell inequalities, POVMs measurements and quantum states.
Analyzing this construction we find that, even though entanglement is necessary
to obtain violation of Bell inequalities, the Entropy of entanglement of the
underlying state is essentially irrelevant in obtaining large violation. We
also indicate why the maximally entangled state is a rather poor candidate in
producing large violations with arbitrary coefficients. However, we also show
that for Bell inequalities with positive coefficients (in particular, games)
the maximally entangled state achieves the largest violation up to a
logarithmic factor.Comment: Reference [16] added. Some typos correcte
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