307 research outputs found
Entanglement witnesses and a loophole problem
We consider a possible detector-efficiency loophole in experiments that
detect entanglement via the local measurement of witness operators. Here, only
local properties of the detectors are known. We derive a general threshold for
the detector efficiencies which guarantees that a negative expectation value of
a witness is due to entanglement, rather than to erroneous detectors. This
threshold depends on the local decomposition of the witness and its measured
expectation value. For two-qubit witnesses we find the local operator
decomposition that is optimal with respect to closing the loophole.Comment: 5 pages, 2 figures, published versio
A redshift survey of IRAS galaxies
Results are presented from a redshift survey of all 72 galaxies detected by IRAS in Band 3 at flux levels equal to or greater then 2 Jy. The luminosity function at the high luminosity end is proportional to L sup -2, however, a flattening was observed at the low luminosity end indicating that a single power law is not a good description of the entire luminosity function. Only three galaxies in the sample have emission line spectra indicative of AGN's, suggesting that, at least in nearby galaxies, unobscured nuclear activity is not a strong contributor to the far infrared flux. Comparisons between the selected IRAS galaxies and an optically complete sample taken from the CfA redshift survey show that they are more narrowly distributed than those optically selected, in the sence that the IRAS sample includes few galaxies of low absolute blue luminosity. It was also found that the space distributions of the two samples differ: the density enhancement or IRAS galaxies is only approx. 1/3 that of the optically selected galaxies in the core of the Coma cluster
Single-attribute utility analysis may be futile, but this can't be the end of the story: causal chain analysis as an aternative
Research on providing singleâattribute utility analysis has shown moderate or even negative effects on the acceptance of selection and training tests by human resource decision makers. In this study, we contrasted the perceived utility of singleâattribute utility analysis with causal chain analysis as an alternative way of conducting utility analysis. Causal chain analysis focuses on measuring the linkages between HRM interventions and organizational outcomes mediated by employee attitudes and customer perceptions. We compared 144 managers' reactions to both methods of utility analysis concerning the variables understandability, information quality, perceived usefulness, user information satisfaction, and intention to use. Causal chain analysis yielded higher results than singleâattribute analysis for these variables, and a compound measure of these constructs supported this finding. This indicates that causal chain analysis is a valuable alternative method of communicating the utility of HRM interventions
Optimal inequalities for state-independent contextuality
Contextuality is a natural generalization of nonlocality which does not need
composite systems or spacelike separation and offers a wider spectrum of
interesting phenomena. Most notably, in quantum mechanics there exist scenarios
where the contextual behavior is independent of the quantum state. We show that
the quest for an optimal inequality separating quantum from classical
noncontextual correlations in an state-independent manner admits an exact
solution, as it can be formulated as a linear program. We introduce the
noncontextuality polytope as a generalization of the locality polytope, and
apply our method to identify two different tight optimal inequalities for the
most fundamental quantum scenario with state-independent contextuality.Comment: REVTeX4.1, 5 pages, 1 figure; v2: improved presentation and
significantly extended result
Compatibility and noncontextuality for sequential measurements
A basic assumption behind the inequalities used for testing noncontextual
hidden variable models is that the observables measured on the same individual
system are perfectly compatible. However, compatibility is not perfect in
actual experiments using sequential measurements. We discuss the resulting
"compatibility loophole" and present several methods to rule out certain hidden
variable models which obey a kind of extended noncontextuality. Finally, we
present a detailed analysis of experimental imperfections in a recent trapped
ion experiment and apply our analysis to that case.Comment: 15 pages, 2 figures, v2: problem with latex solve
Typical local measurements in generalised probabilistic theories: emergence of quantum bipartite correlations
What singles out quantum mechanics as the fundamental theory of Nature? Here
we study local measurements in generalised probabilistic theories (GPTs) and
investigate how observational limitations affect the production of
correlations. We find that if only a subset of typical local measurements can
be made then all the bipartite correlations produced in a GPT can be simulated
to a high degree of accuracy by quantum mechanics. Our result makes use of a
generalisation of Dvoretzky's theorem for GPTs. The tripartite correlations can
go beyond those exhibited by quantum mechanics, however.Comment: 5 pages, 1 figure v2: more details in the proof of the main resul
ESO Imaging Survey: infrared observations of CDF-S and HDF-S
This paper presents infrared data obtained from observations carried out at
the ESO 3.5m New Technology Telescope (NTT) of the Hubble Deep Field South
(HDF-S) and the Chandra Deep Field South (CDF-S). These data were taken as part
of the ESO Imaging Survey (EIS) program, a public survey conducted by ESO to
promote follow-up observations with the VLT. In the HDF-S field the infrared
observations cover an area of ~53 square arcmin, encompassing the HST WFPC2 and
STIS fields, in the JHKs passbands. The seeing measured in the final stacked
images ranges from 0.79" to 1.22" and the median limiting magnitudes (AB
system, 2" aperture, 5sigma detection limit) are J_AB~23.0, H_AB~22.8 and
K_AB~23.0 mag. Less complete data are also available in JKs for the adjacent
HST NICMOS field. For CDF-S, the infrared observations cover a total area of
\~100 square arcmin, reaching median limiting magnitudes (as defined above) of
J_AB~23.6 and K_AB~22.7 mag. For one CDF-S field H-band data are also
available. This paper describes the observations and presents the results of
new reductions carried out entirely through the un-supervised, high-throughput
EIS Data Reduction System and its associated EIS/MVM C++-based image processing
library developed, over the past 5 years, by the EIS project and now publicly
available. The paper also presents source catalogs extracted from the final
co-added images which are used to evaluate the scientific quality of the survey
products, and hence the performance of the software. This is done comparing the
results obtained in the present work with those obtained by other authors from
independent data and/or reductions carried out with different software packages
and techniques. The final science-grade catalogs and co-added images are
available at CDS.Comment: Accepted for publication in A&A, 13 pages, 12 figures; a full
resolution version of the paper is available from
http://www.astro.ku.dk/~lisbeth/eisdata/papers/4528.pdf ; related catalogs
and images are available through http://www.astro.ku.dk/~lisbeth/eisdata
Relativistic analysis of the 208Pb(e,e'p)207Tl reaction at high momentum
The recent 208Pb(e,e'p)207Tl data from NIKHEF-K at high missing momentum
(p_m>300 MeV/c) are compared to theoretical results obtained with a fully
relativistic formalism previously applied to analyze data on the low missing
momentum (p_m < 300 MeV/c) region. The same relativistic optical potential and
mean field wave functions are used in the two p_m-regions. The spectroscopic
factors of the various shells are extracted from the analysis of the low-p_m
data and then used in the high-p_m region. In contrast to previous analyses
using a nonrelativistic mean field formalism, we do not find a substantial
deviation from the mean field predictions other than that of the spectroscopic
factors, which appear to be consistent with both low- and high-p_m data. We
find that the difference between results of relativistic and nonrelativistic
formalisms is enhanced in the p_m<0 region that will be interesting to explore
experimentally.Comment: 12 pages, LaTeX+Revtex, included 3 postscript figures. To appear in
the Physical Review C (Rapid Communications
A framework for bounding nonlocality of state discrimination
We consider the class of protocols that can be implemented by local quantum
operations and classical communication (LOCC) between two parties. In
particular, we focus on the task of discriminating a known set of quantum
states by LOCC. Building on the work in the paper "Quantum nonlocality without
entanglement" [BDF+99], we provide a framework for bounding the amount of
nonlocality in a given set of bipartite quantum states in terms of a lower
bound on the probability of error in any LOCC discrimination protocol. We apply
our framework to an orthonormal product basis known as the domino states and
obtain an alternative and simplified proof that quantifies its nonlocality. We
generalize this result for similar bases in larger dimensions, as well as the
"rotated" domino states, resolving a long-standing open question [BDF+99].Comment: 33 pages, 7 figures, 1 tabl
Separable Dual Space Gaussian Pseudo-potentials
We present pseudo-potential coefficients for the first two rows of the
periodic table. The pseudo potential is of a novel analytic form, that gives
optimal efficiency in numerical calculations using plane waves as basis set. At
most 7 coefficients are necessary to specify its analytic form. It is separable
and has optimal decay properties in both real and Fourier space. Because of
this property, the application of the nonlocal part of the pseudo-potential to
a wave-function can be done in an efficient way on a grid in real space. Real
space integration is much faster for large systems than ordinary multiplication
in Fourier space since it shows only quadratic scaling with respect to the size
of the system. We systematically verify the high accuracy of these
pseudo-potentials by extensive atomic and molecular test calculations.Comment: 16 pages, 4 postscript figure
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