351 research outputs found
Nonlinear nanomechanical resonators for quantum optoelectromechanics
We present a scheme for tuning and controlling nano mechanical resonators by
subjecting them to electrostatic gradient fields, provided by nearby tip
electrodes. We show that this approach enables access to a novel regime of
optomechanics, where the intrinsic nonlinearity of the nanoresonator can be
explored. In this regime, one or several laser driven cavity modes coupled to
the nanoresonator and suitably adjusted gradient fields allow to control the
motional state of the nanoresonator at the single phonon level. Some
applications of this platform have been presented previously [New J. Phys. 14,
023042 (2012), Phys. Rev. Lett. 110, 120503 (2013)]. Here, we provide a
detailed description of the corresponding setup and its optomechanical coupling
mechanisms, together with an in-depth analysis of possible sources of damping
or decoherence and a discussion of the readout of the nanoresonator state.Comment: 15 pages, 6 figure
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Effects of classification context on categorization in natural categories
The patterns of classification of borderline instances of eight common taxonomic categories were examined under three different instructional conditions to test two predictions: first, that lack of a specified context contributes to vagueness in categorization, and second, that altering the purpose of classification can lead to greater or lesser dependence on similarity in classification. The instructional conditions contrasted purely pragmatic with more technical/quasi-legal contexts as purposes for classification, and these were compared with a no-context control. The measures of category vagueness were between-subjects disagreement and within-subjects consistency, and the measures of similarity based categorization were category breadth and the correlation of instance categorization probability with mean rated typicality, independently measured in a neutral context. Contrary to predictions, none of the measures of vagueness, reliability, category breadth, or correlation with typicality were generally affected by the instructional setting as a function of pragmatic versus technical purposes. Only one subcondition, in which a situational context was implied in addition to a purposive context, produced a significant change in categorization. Further experiments demonstrated that the effect of context was not increased when participants talked their way through the task, and that a technical context did not elicit more all-or-none categorization than did a pragmatic context. These findings place an important boundary condition on the effects of instructional context on conceptual categorization
Quantum Structure in Cognition: Why and How Concepts are Entangled
One of us has recently elaborated a theory for modelling concepts that uses
the state context property (SCoP) formalism, i.e. a generalization of the
quantum formalism. This formalism incorporates context into the mathematical
structure used to represent a concept, and thereby models how context
influences the typicality of a single exemplar and the applicability of a
single property of a concept, which provides a solution of the 'Pet-Fish
problem' and other difficulties occurring in concept theory. Then, a quantum
model has been worked out which reproduces the membership weights of several
exemplars of concepts and their combinations. We show in this paper that a
further relevant effect appears in a natural way whenever two or more concepts
combine, namely, 'entanglement'. The presence of entanglement is explicitly
revealed by considering a specific example with two concepts, constructing some
Bell's inequalities for this example, testing them in a real experiment with
test subjects, and finally proving that Bell's inequalities are violated in
this case. We show that the intrinsic and unavoidable character of entanglement
can be explained in terms of the weights of the exemplars of the combined
concept with respect to the weights of the exemplars of the component concepts.Comment: 10 page
Assessing Semantic Similarities among Geospatial Feature Class Definitions
The assessment of semantic similarity among objects is a basic requirement for semantic interoperability. This paper presents an innovative approach to semantic similarity assessment by combining the advantages of two different strategies: featurematching process and semantic distance calculation. The model involves a knowledge base of spatial concepts that consists of semantic relations (is-a and part-whole) and distinguishing features (functions, parts, and attributes). By taking into consideration cognitive properties of similarity assessments, this model expects to represent a cognitively plausible and computationally achievable method for measuring the degree of interoperability
Feature integration in natural language concepts
Two experiments measured the joint influence of three key sets of semantic features on the frequency with which artifacts (Experiment 1) or plants and creatures (Experiment 2) were categorized in familiar categories. For artifacts, current function outweighed both originally intended function and current appearance. For biological kinds, appearance and behavior, an inner biological function, and appearance and behavior of offspring all had similarly strong effects on categorization. The data were analyzed to determine whether an independent cue model or an interactive model best accounted for how the effects of the three feature sets combined. Feature integration was found to be additive for artifacts but interactive for biological kinds. In keeping with this, membership in contrasting artifact categories tended to be superadditive, indicating overlapping categories, whereas for biological kinds, it was subadditive, indicating conceptual gaps between categories. It is argued that the results underline a key domain difference between artifact and biological concepts
Classical Logical versus Quantum Conceptual Thought: Examples in Economics, Decision theory and Concept Theory
Inspired by a quantum mechanical formalism to model concepts and their
disjunctions and conjunctions, we put forward in this paper a specific
hypothesis. Namely that within human thought two superposed layers can be
distinguished: (i) a layer given form by an underlying classical deterministic
process, incorporating essentially logical thought and its indeterministic
version modeled by classical probability theory; (ii) a layer given form under
influence of the totality of the surrounding conceptual landscape, where the
different concepts figure as individual entities rather than (logical)
combinations of others, with measurable quantities such as 'typicality',
'membership', 'representativeness', 'similarity', 'applicability', 'preference'
or 'utility' carrying the influences. We call the process in this second layer
'quantum conceptual thought', which is indeterministic in essence, and contains
holistic aspects, but is equally well, although very differently, organized
than logical thought. A substantial part of the 'quantum conceptual thought
process' can be modeled by quantum mechanical probabilistic and mathematical
structures. We consider examples of three specific domains of research where
the effects of the presence of quantum conceptual thought and its deviations
from classical logical thought have been noticed and studied, i.e. economics,
decision theory, and concept theories and which provide experimental evidence
for our hypothesis.Comment: 14 page
Iterative algorithm versus analytic solutions of the parametrically driven dissipative quantum harmonic oscillator
We consider the Brownian motion of a quantum mechanical particle in a
one-dimensional parabolic potential with periodically modulated curvature under
the influence of a thermal heat bath. Analytic expressions for the
time-dependent position and momentum variances are compared with results of an
iterative algorithm, the so-called quasiadiabatic propagator path integral
algorithm (QUAPI). We obtain good agreement over an extended range of
parameters for this spatially continuous quantum system. These findings
indicate the reliability of the algorithm also in cases for which analytic
results may not be available a priori.Comment: 15 pages including 11 figures, one reference added, minor typos
correcte
Cumulant Expansions and the Spin-Boson Problem
The dynamics of the dissipative two-level system at zero temperature is
studied using three different cumulant expansion techniques. The relative
merits and drawbacks of each technique are discussed. It is found that a new
technique, the non-crossing cumulant expansion, appears to embody the virtues
of the more standard cumulant methods.Comment: 26 pages, LaTe
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