2,834 research outputs found
Limit quantum efficiency for violation of Clauser-Horne Inequality for qutrits
In this paper we present the results of numerical calculations about the
minimal value of detection efficiency for violating the Clauser - Horne
inequality for qutrits. Our results show how the use of non-maximally entangled
states largely improves this limit respect to maximally entangled ones. A
stronger resistance to noise is also found.Comment: Phys. Rev. A in pres
Multiquark Systems in a Constituent Quark Model with Chiral Dynamics
We discuss the stability of multiquark systems within the recent model of
Glozman et al. where the chromomagnetic hyperfine interaction is replaced by
pseudoscalar-meson exchange. We find that such an interaction binds a heavy
tetraquark system ( and by GeV.
This is at variance with results of previous models where is
unstable.Comment: 6 pages, Plain Latex, Contribution to the Workshop''Quark Confinement
and the Hadron Spectrum II'', Como, Italy, June 26--29, 1996, to appear in
the Proceedings, ed. Nora Brambilla, World Scientifi
Heavy-Flavour Pentaquarks in a Chiral Constituent Quark Model
Within the chiral constituent quark model of Glozman and Riska, we discuss
the stability of heavy pentaquarks, i.e. hadrons containing four light quarks
and a heavy antiquark. The spin-dependent part of the Hamiltonian is dominated
by the short-range part of the Goldstone-boson-exchange interaction. We find
that these systems are not bound, having an energy above the lowest
dissociation threshold into a baryon and a meson.Comment: 10 pages + table
A new source detection algorithm using FDR
The False Discovery Rate (FDR) method has recently been described by Miller
et al (2001), along with several examples of astrophysical applications. FDR is
a new statistical procedure due to Benjamini and Hochberg (1995) for
controlling the fraction of false positives when performing multiple hypothesis
testing. The importance of this method to source detection algorithms is
immediately clear. To explore the possibilities offered we have developed a new
task for performing source detection in radio-telescope images, Sfind 2.0,
which implements FDR. We compare Sfind 2.0 with two other source detection and
measurement tasks, Imsad and SExtractor, and comment on several issues arising
from the nature of the correlation between nearby pixels and the necessary
assumption of the null hypothesis. The strong suggestion is made that
implementing FDR as a threshold defining method in other existing
source-detection tasks is easy and worthwhile. We show that the constraint on
the fraction of false detections as specified by FDR holds true even for highly
correlated and realistic images. For the detection of true sources, which are
complex combinations of source-pixels, this constraint appears to be somewhat
less strict. It is still reliable enough, however, for a priori estimates of
the fraction of false source detections to be robust and realistic.Comment: 17 pages, 7 figures, accepted for publication by A
Measuring the photon distribution by ON/OFF photodectors
Reconstruction of photon statistics of optical states provide fundamental
information on the nature of any optical field and find various relevant
applications. Nevertheless, no detector that can reliably discriminate the
number of incident photons is available. On the other hand the alternative of
reconstructing density matrix by quantum tomography leads to various technical
difficulties that are particular severe in the pulsed regime (where mode
matching between signal an local oscillator is very challenging). Even if
on/off detectors, as usual avalanche PhotoDiodes operating in Geiger mode, seem
useless as photocounters, recently it was shown how reconstruction of photon
statistics is possible by considering a variable quantum efficiency. Here we
present experimental reconstructions of photon number distributions of both
continuous-wave and pulsed light beams in a scheme based on on/off avalanche
photodetection assisted by maximum-likelihood estimation. Reconstructions of
the distribution for both semiclassical and quantum states of light (as single
photon, coherent, pseudothermal and multithermal states) are reported for
single-mode as well as for multimode beams. The stability and good accuracy
obtained in the reconstruction of these states clearly demonstrate the
interesting potentialities of this simple technique.Comment: 6 pages, 7 figures, to appear on Laser Physic
Isospin Splittings of Baryons
We discuss the isospin-breaking mass differences among baryons, with
particular attention in the charm sector to the ,
, and splittings. Simple potential
models cannot accommodate the trend of the available data on charm baryons.
More precise measurements would offer the possibility of testing how well
potential models describe the non-perturbative limit of QCD.Comment: 4 pages, aipproc.sty, Proceeding of Hadron 9
Baryons Electromagnetic Mass Splittings in Potential Models
We study electromagnetic mass splittings of charmed baryons. We point out
discrepancies among theoretical predictions in non-relativistic potential
models. None of them seems supported by experimental data. A new calculation is
presented.Comment: 4 pages, Proc. of ISS97 Tashkent 6-13 Oct. 9
Optimal Control of Superconducting N-level quantum systems
We consider a current-biased dc SQUID in the presence of an applied
time-dependent bias current or magnetic flux. The phase dynamics of such a
Josephson device is equivalent to that of a quantum particle trapped in a D
anharmonic potential, subject to external time-dependent control fields, {\it
i.e.} a driven multilevel quantum system. The problem of finding the required
time-dependent control field that will steer the system from a given initial
state to a desired final state at a specified final time is formulated in the
framework of optimal control theory. Using the spectral filter technique, we
show that the selected optimal field which induces a coherent population
transfer between quantum states is represented by a carrier signal having a
constant frequency but which is time-varied both in amplitude and phase. The
sensitivity of the optimal solution to parameter perturbations is also
addressed
The functional relevance of olfactory marker protein in the vertebrate olfactory system: a never-ending story
Olfactory marker protein (OMP) was first described as a protein expressed in olfactory receptor neurons (ORNs) in the nasal cavity. In particular, OMP, a small cytoplasmic protein, marks mature ORNs and is also expressed in the neurons of other nasal chemosensory systems: the vomeronasal organ, the septal organ of Masera, and the Grueneberg ganglion. While its expression pattern was more easily established, OMPâs function remained relatively vague. To date, most of the work to understand OMPâs role has been done using mice lacking OMP. This mostly phenomenological work has shown that OMP is involved in sharpening the odorant response profile and in quickening odorant response kinetics of ORNs and that it contributes to targeting of ORN axons to the olfactory bulb to refine the glomerular response map. Increasing evidence shows that OMP acts at the early stages of olfactory transduction by modulating the kinetics of cAMP, the second messenger of olfactory transduction. However, how this occurs at a mechanistic level is not understood, and it might also not be the only mechanism underlying all the changes observed in mice lacking OMP. Recently, OMP has been detected outside the nose, including the brain and other organs. Although no obvious logic has become apparent regarding the underlying commonality between nasal and extranasal expression of OMP, a broader approach to diverse cellular systems might help unravel OMPâs functions and mechanisms of action inside and outside the nose
Generation of different Bell states within the SPDC phase-matching bandwidth
We study the frequency-angular lineshape for a phase-matched nonlinear
process producing entangled states and show that there is a continuous variety
of maximally-entangled states generated for different mismatch values within
the natural bandwidth. Detailed considerations are made for two specific
methods of polarization entanglement preparation, based on type-II spontaneous
parametric down-conversion (SPDC) and on SPDC in two subsequent type-I crystals
producing orthogonally polarized photon pairs. It turns out that different Bell
states are produced at the center of the SPDC line and on its slopes,
corresponding to about half-maximum intensity level. These Bell states can be
filtered out by either frequency selection or angular selection, or both. Our
theoretical calculations are confirmed by a series of experiments, performed
for the two above-mentioned schemes of producing polarization-entangled photon
pairs and with two kinds of measurements: frequency-selective and
angular-selective.Comment: submitted for publicatio
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