54 research outputs found
Interferometric Tests of Teleportation
We investigate a direct test of teleportation efficacy based on a
Mach-Zehnder interferometer. The analysis is performed for continuous variable
teleportation of both discrete and continuous observables
Numerical analyses of the nonequilibrium electron transport through the Kondo impurity beside the Toulouse point
Nonequilibrium electron transport through the Kondo impurity is investigated
numerically for the system with twenty conduction-electron levels. The electron
current under finite voltage drop is calculated in terms of the `conductance
viewed as transmission' picture proposed by Landauer. Here, we take into
account the full transmission processes of both the many-body correlation and
the hybridization amplitude up to infinite order. Our results demonstrate, for
instance, how the exact solution of the differential conductance by Schiller
and Hershfield obtained at the Toulouse point becomes deformed by more
realistic interactions. The differential-conductance-peak height is suppressed
below e^2/h with the width hardly changed through reducing the Kondo coupling
from the Toulouse point, whereas it is kept unchanged by further increase of
the coupling. We calculated the nonequilibrium local Green function as well.
This clarifies the spectral property of the Kondo impurity driven far from
equilibrium
Remembering 'zeal' but not 'thing':reverse frequency effects as a consequence of deregulated semantic processing
More efficient processing of high frequency (HF) words is a ubiquitous finding in healthy individuals, yet frequency effects are often small or absent in stroke aphasia. We propose that some patients fail to show the expected frequency effect because processing of HF words places strong demands on semantic control and regulation processes, counteracting the usual effect. This may occur because HF words appear in a wide range of linguistic contexts, each associated with distinct semantic information. This theory predicts that in extreme circumstances, patients with impaired semantic control should show an outright reversal of the normal frequency effect. To test this prediction, we tested two patients with impaired semantic control with a delayed repetition task that emphasised activation of semantic representations. By alternating HF and low frequency (LF) trials, we demonstrated a significant repetition advantage for LF words, principally because of perseverative errors in which patients produced the previous LF response in place of the HF target. These errors indicated that HF words were more weakly activated than LF words. We suggest that when presented with no contextual information, patients generate a weak and unstable pattern of semantic activation for HF words because information relating to many possible contexts and interpretations is activated. In contrast, LF words tend are associated with more stable patterns of activation because similar semantic information is activated whenever they are encountered
Quantum Optical Systems for the Implementation of Quantum Information Processing
We review the field of Quantum Optical Information from elementary
considerations through to quantum computation schemes. We illustrate our
discussion with descriptions of experimental demonstrations of key
communication and processing tasks from the last decade and also look forward
to the key results likely in the next decade. We examine both discrete (single
photon) type processing as well as those which employ continuous variable
manipulations. The mathematical formalism is kept to the minimum needed to
understand the key theoretical and experimental results
Semantic diversity:A measure of contextual variation in word meaning based on latent semantic analysis
Kondo-resonance, Coulomb blockade, and Andreev transport through a quantum dot
We study resonant tunneling through an interacting quantum dot coupled to
normal metallic and superconducting leads. We show that large Coulomb
interaction gives rise to novel effects in Andreev transport. Adopting an exact
relation for the Green's function, we find that at zero temperature, the linear
response conductance is enhanced due to Kondo-Andreev resonance in the Kondo
limit, while it is suppressed in the empty site limit. In the Coulomb blockaded
region, on the other hand, the conductance is reduced more than the
corresponding conductance with normal leads because large charging energy
suppresses Andreev reflection.Comment: 3 pages Revtex, 4 Postscript figures, accepted for publication in
Phys. Rev.
Evidence for saturation of channel transmission from conductance fluctuations in atomic-size point contacts
The conductance of atomic size contacts has a small, random, voltage
dependent component analogous to conductance fluctuations observed in diffusive
wires (UCF). A new effect is observed in gold contacts, consisting of a marked
suppression of these fluctuations when the conductance of the contact is close
to integer multiples of the conductance quantum. Using a model based on the
Landauer-Buettiker formalism we interpret this effect as evidence that the
conductance tends to be built up from fully transmitted (i.e., saturated)
channels plus a single, which is partially transmitted.Comment: An error in Eq.(2) was corrected, where a square root was added to
the factor (1-cos(gamma)). This results in a revised estimate for the mean
free path of 5 nm, which is now fully consistent with the estimates from the
series resistance and the thermopowe
Resonant multiple Andreev reflections in mesoscopic superconducting junctions
We investigate the properties of subharmonic gap structure (SGS) in
superconducting quantum contacts with normal-electron resonances. We find two
distinct new features of the SGS in resonant junctions which distinguish them
from non-resonant point contacts: (i) The odd-order structures on the
current-voltage characteristics of resonant junctions are strongly enhanced and
have pronounced peaks, while the even-order structures are suppressed, in the
case of a normal electron resonance being close to the Fermi level. (ii)
Tremendous current peaks develop at where indicates a
distance of the resonance to the Fermi level. These properties are determined
by the effect of narrowing of the resonance during multiple Andreev reflections
and by overlap of electron and hole resonances.Comment: 13 pages, 10 figure
On staying grounded and avoiding Quixotic dead ends
The 15 articles in this special issue on The Representation of Concepts illustrate the rich variety of theoretical positions and supporting research that characterize the area. Although much agreement exists among contributors, much disagreement exists as well, especially about the roles of grounding and abstraction in conceptual processing. I first review theoretical approaches raised in these articles that I believe are Quixotic dead ends, namely, approaches that are principled and inspired but likely to fail. In the process, I review various theories of amodal symbols, their distortions of grounded theories, and fallacies in the evidence used to support them. Incorporating further contributions across articles, I then sketch a theoretical approach that I believe is likely to be successful, which includes grounding, abstraction, flexibility, explaining classic conceptual phenomena, and making contact with real-world situations. This account further proposes that (1) a key element of grounding is neural reuse, (2) abstraction takes the forms of multimodal compression, distilled abstraction, and distributed linguistic representation (but not amodal symbols), and (3) flexible context-dependent representations are a hallmark of conceptual processing
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