3,093 research outputs found
Intensity correlations, entanglement properties and ghost imaging in multimode thermal-seeded parametric downconversion: Theory
We address parametric-downconversion seeded by multimode pseudo-thermal
fields. We show that this process may be used to generate multimode pairwise
correlated states with entanglement properties that can be tuned by controlling
the seed intensities. Multimode pseudo-thermal fields seeded
parametric-downconversion represents a novel source of correlated states, which
allows one to explore the classical-quantum transition in pairwise correlations
and to realize ghost imaging and ghost diffraction in regimes not yet explored
by experiments.Comment: 9 pages, 3 figure
Experimental reconstruction of photon statistics without photon counting
Experimental reconstructions of photon number distributions of both
continuous-wave and pulsed light beams are reported. Our scheme is based on
on/off avalanche photodetection assisted by maximum-likelihood estimation and
does not involve photon counting. Reconstructions of the distribution for both
semiclassical and quantum states of light are reported for single-mode as well
as for multimode beams.Comment: Revised version: in press on PRL. 4 pages, 4 fig
Conditional measurements on multimode pairwise entangled states from spontaneous parametric downconversion
We address the intrinsic multimode nature of the quantum state of light
obtained by pulsed spontaneous parametric downconversion and develop a
theoretical model based only on experimentally accessible quantities. We
exploit the pairwise entanglement as a resource for conditional multimode
measurements and derive closed formulas for the detection probability and the
density matrix of the conditional states. We present a set of experiments
performed to validate our model in different conditions that are in excellent
agreement with experimental data. Finally, we evaluate nonGaussianity of the
conditional states obtained from our source with the aim of discussing the
effects of the different experimental parameters on the efficacy of this type
of conditional state preparation
The quantum-classical transition in thermally seeded parametric downconversion
We address the pair of conjugated field modes obtained from
parametric-downconversion as a convenient system to analyze the
quantum-classical transition in the continuous variable regime. We explicitly
evaluate intensity correlations, negativity and entanglement for the system in
a thermal state and show that a hierarchy of nonclassicality thresholds
naturally emerges in terms of thermal and downconversion photon number. We show
that the transition from quantum to classical regime may be tuned by
controlling the intensities of the seeds and detected by intensity
measurements. Besides, we show that the thresholds are not affected by losses,
which only modify the amount of nonclassicality. The multimode case is also
analyzed in some detail.Comment: 12 pages, 3 figure
Robot adoption and FDI driven transformation in the automotive industry
This paper explores the relationship between inward foreign direct investments and the adoption of industrial robots, across different segments of the automotive value chain. Using the International Federation of Robotics and FDI Market datasets at a fine level of disaggregation of the automotive sector, we investigate the extent to which FDIs are related to the operational stock of industrial robots in 34 countries over the period 2005-2014. We find distinct patterns linking FDIs and robot adoption for different groups of countries and for different segments of the automotive value chain, that, is assembling and components production. With some relevant exceptions, FDIs are found to be highly correlated with robot adoption in the assembling segment across major leading countries. However, this correlation becomes weak for components production. To explain this differential role of FDIs in robot adoption, we formulate hypotheses around the country-specific drivers of robotisation for the components segment by pointing to the role of domestic ecosystems of suppliers and industrial policy as drivers of technology absorption and diffusion
Reliable source of conditional non-Gaussian states from single-mode thermal fields
We address both theoretically and experimentally the generation of pulsed
non-Gaussian states from classical Gaussian ones by means of conditional
measurements. The setup relies on a beam splitter and a pair of linear
photodetectors able to resolve up to tens of photons in the two outputs. We
show the reliability of the setup and the good agreement with the theory for a
single-mode thermal field entering the beam splitter and present a thorough
characterization of the photon statistics of the conditional states.Comment: 18 pages, 12 figure
The quantum-classical transition in thermally seeded parametric downconversion
We address the pair of conjugated field modes obtained from
parametric-downconversion as a convenient system to analyze the
quantum-classical transition in the continuous variable regime. We explicitly
evaluate intensity correlations, negativity and entanglement for the system in
a thermal state and show that a hierarchy of nonclassicality thresholds
naturally emerges in terms of thermal and downconversion photon number. We show
that the transition from quantum to classical regime may be tuned by
controlling the intensities of the seeds and detected by intensity
measurements. Besides, we show that the thresholds are not affected by losses,
which only modify the amount of nonclassicality. The multimode case is also
analyzed in some detail.Comment: 12 pages, 3 figure
State reconstruction by on/off measurements
We demonstrate a state reconstruction technique which provides either the
Wigner function or the density matrix of a field mode and requires only
avalanche photodetectors, without any phase or amplitude discrimination power.
It represents an alternative, of simpler implementation, to quantum homodyne
tomography.Comment: 6 pages, 4 figures, revised and enlarged versio
Ab initio Molecular Dynamics in Adaptive Coordinates
We present a new formulation of ab initio molecular dynamics which exploits
the efficiency of plane waves in adaptive curvilinear coordinates, and thus
provides an accurate treatment of first-row elements. The method is used to
perform a molecular dynamics simulation of the CO_2 molecule, and allows to
reproduce detailed features of its vibrational spectrum such as the splitting
of the Raman sigma+_g mode caused by Fermi resonance. This new approach opens
the way to highly accurate ab initio simulations of organic compounds.Comment: 11 pages, 3 PostScript figure
Sub-shot-noise photon-number correlation in mesoscopic twin-beam of light
We demonstrate sub-shot-noise photon-number correlations in a (temporal)
multimode mesoscopic ( detected photons) twin-beam produced by
ps-pulsed spontaneous non-degenerate parametric downconversion. We have
separately detected the signal and idler distributions of photons collected in
twin coherence areas and found that the variance of the photon-count difference
goes below the shot-noise limit by 3.25 dB. The number of temporal modes
contained in the twin-beam, as well as the size of the twin coherence areas,
depends on the pump intensity. Our scheme is based on spontaneous
downconversion and thus does not suffer from limitations due to the finite gain
of the parametric process. Twin-beams are also used to demonstrate the
conditional preparation of a nonclassical (sub-Poissonian) state.Comment: 5 pages, 5 (low-res) figures, to appear on PR
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