1,095 research outputs found
Quality of a Which-Way Detector
We introduce a measure Q of the "quality" of a quantum which-way detector,
which characterizes its intrinsic ability to extract which-way information in
an asymmetric two-way interferometer. The "quality" Q allows one to separate
the contribution to the distinguishability of the ways arising from the quantum
properties of the detector from the contribution stemming from a-priori
which-way knowledge available to the experimenter, which can be quantified by a
predictability parameter P. We provide an inequality relating these two sources
of which-way information to the value of the fringe visibility displayed by the
interferometer. We show that this inequality is an expression of duality,
allowing one to trace the loss of coherence to the two reservoirs of which-way
information represented by Q and P. Finally, we illustrate the formalism with
the use of a quantum logic gate: the Symmetric Quanton-Detecton System (SQDS).
The SQDS can be regarded as two qubits trying to acquire which way information
about each other. The SQDS will provide an illustrating example of the
reciprocal effects induced by duality between system and which-way detector.Comment: 10 pages, 5 figure
Microscopic chaos from Brownian motion?
A recent experiment on Brownian motion has been interpreted to exhibit direct
evidence for microscopic chaos. In this note we demonstrate that virtually
identical results can be obtained numerically using a manifestly
microscopically nonchaotic system.Comment: 3 pages, 1 figure, Comment on P. Gaspard et al, Nature vol 394, 865
(1998); rewritten in a more popular styl
Mutations in SPG11, encoding spatacsin, are a major cause of spastic paraplegia with thin corpus callosum.
Autosomal recessive hereditary spastic paraplegia (ARHSP) with thin corpus
callosum (TCC) is a common and clinically distinct form of familial spastic
paraplegia that is linked to the SPG11 locus on chromosome 15 in most affected
families. We analyzed 12 ARHSP-TCC families, refined the SPG11 candidate interval
and identified ten mutations in a previously unidentified gene expressed
ubiquitously in the nervous system but most prominently in the cerebellum,
cerebral cortex, hippocampus and pineal gland. The mutations were either nonsense
or insertions and deletions leading to a frameshift, suggesting a
loss-of-function mechanism. The identification of the function of the gene will
provide insight into the mechanisms leading to the degeneration of the
corticospinal tract and other brain structures in this frequent form of ARHSP
Spectra of heavy-light and heavy-heavy mesons containing charm quarks, including higher spin states for
We study the spectra of heavy-light and heavy-heavy mesons containing charm
quarks, including higher spin states. We use two sets of gauge
configurations, one set from QCDSF using the SLiNC action, and the other
configurations from the Budapest-Marseille-Wuppertal collaboration, using the
HEX smeared clover action. To extract information about the excited states, we
choose a suitable basis of operators to implement the variational method.Comment: 7 pages, 5 figures, Talk presented at the XXIX International
Symposium on Lattice Field Theory, Lattice2011, July 11-16, 2011, The Village
at Squaw Valley, California, US
Light Hadron Masses from Lattice QCD
This article reviews lattice QCD results for the light hadron spectrum. We
give an overview of different formulations of lattice QCD, with discussions on
the fermion doubling problem and improvement programs. We summarize recent
developments in algorithms and analysis techniques, that render calculations
with light, dynamical quarks feasible on present day computer resources.
Finally, we summarize spectrum results for ground state hadrons and resonances
using various actions.Comment: 53 pages, 24 figures, one table; Rev.Mod.Phys. (published version);
v2: corrected typ
Longitudinal changes in functional connectivity of cortico-basal ganglia networks in manifests and premanifest huntington's disease
Huntington's disease (HD) is a genetic neurological disorder resulting in cognitive and motor impairments. We evaluated the longitudinal changes of functional connectivity in sensorimotor, associative and limbic cortico-basal ganglia networks. We acquired structural MRI and resting-state fMRI in three visits one year apart, in 18 adult HD patients, 24 asymptomatic mutation carriers (preHD) and 18 gender- and age-matched healthy volunteers from the TRACK-HD study. We inferred topological changes in functional connectivity between 182 regions within cortico-basal ganglia networks using graph theory measures. We found significant differences for global graph theory measures in HD but not in preHD. The average shortest path length (L) decreased, which indicated a change toward the random network topology. HD patients also demonstrated increases in degree k, reduced betweeness centrality bc and reduced clustering C. Changes predominated in the sensorimotor network for bc and C and were observed in all circuits for k. Hubs were reduced in preHD and no longer detectable in HD in the sensorimotor and associative networks. Changes in graph theory metrics (L, k, C and bc) correlated with four clinical and cognitive measures (symbol digit modalities test, Stroop, Burden and UHDRS). There were no changes in graph theory metrics across sessions, which suggests that these measures are not reliable biomarkers of longitudinal changes in HD. preHD is characterized by progressive decreasing hub organization, and these changes aggravate in HD patients with changes in local metrics. HD is characterized by progressive changes in global network interconnectivity, whose network topology becomes more random over time. Hum Brain Mapp, 2016. © 2016 Wiley Periodicals, Inc
Testing sequential quantum measurements: how can maximal knowledge be extracted?
The extraction of information from a quantum system unavoidably implies a
modification of the measured system itself. It has been demonstrated recently
that partial measurements can be carried out in order to extract only a portion
of the information encoded in a quantum system, at the cost of inducing a
limited amount of disturbance. Here we analyze experimentally the dynamics of
sequential partial measurements carried out on a quantum system, focusing on
the trade-off between the maximal information extractable and the disturbance.
In particular we consider two different regimes of measurement, demonstrating
that, by exploiting an adaptive strategy, an optimal trade-off between the two
quantities can be found, as observed in a single measurement process. Such
experimental result, achieved for two sequential measurements, can be extended
to N measurement processes.Comment: 5 pages, 3 figure
Filtered overlap: speedup, locality, kernel non-normality and Z_A~1
We investigate the overlap operator with a UV filtered Wilson kernel. The
filtering leads to a better localization of the operator even on coarse
lattices and with the untuned choice . Furthermore, the axial-vector
renormalization constant is much closer to 1, reducing the mismatch with
perturbation theory. We show that all these features persist over a wide range
of couplings and that the details of filtering prove immaterial. We investigate
the properties of the kernel spectrum and find that the kernel non-normality is
reduced. As a side effect we observe that for certain applications of the
filtered overlap a speed-up factor of 2-4 can be achieved.Comment: 30 pp, 23 fig
Quantum decoherence of excitons in a leaky cavity with quasimode
For the excitons in the quantum well placed within a leaky cavity, the
quantum decoherence of a mesoscopically superposed states is investigated based
on the factorization theory for quantum dissipation. It is found that the
coherence of the exciton superposition states will decrease in an oscillating
form when the cavity field interacting with the exciton is of the form of
quasimode. The effect of the thermal cavity fields on the quantum decoherence
of the superposition states of the exciton is studied and it is observed that
the higher the temperature of the environment is, the shorter the decoherence
characteristic time is.Comment: 1 figure, 7 page
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