738 research outputs found
Continuous variable quantum teleportation with sculptured and noisy non-Gaussian resources
We investigate continuous variable (CV) quantum teleportation using relevant
classes of non-Gaussian states of the radiation field as entangled resources.
First, we introduce the class two-mode squeezed symmetric superposition of Fock
states, including finite truncations of twin-beam Gaussian states as special
realizations. These states depend on a set of free independent parameters that
can be adjusted for the optimization of teleportation protocols, with an
enhancement of the success probability of teleportation both for coherent and
Fock input states. We show that the optimization procedure reduces the
entangled resources to truncated twin beam states, which thus represents an
optimal class of non-Gaussian resources for quantum teleportation. We then
introduce a further class of two-mode non-Gaussian entangled resources, in the
form of squeezed cat-like states. We analyze the performance and the properties
of such states when optimized for (CV) teleportation, and compare them to the
optimized squeezed Bell-like states introduced in a previous work
\cite{CVTelepNoi}. We discuss how optimal resources for teleportation are
characterized by a suitable balance of entanglement content and squeezed vacuum
affinity. We finally investigate the effects of thermal noise on the efficiency
of quantum teleportation. To this aim, a convenient framework is to describe
noisy entangled resources as linear superpositions of non-Gaussian state and
thermal states. Although the presence of the thermal component strongly reduces
the teleportation fidelity, noisy non-Gaussian states remain preferred
resources when compared to noisy twin-beam Gaussian states.Comment: 11 pages, 8 figures. Largely revised and expanded version. New
material and sections added. To appear in EPJ-ST (Proceedings of the Central
European Workshop on Quantum Optics 2007. 14th Edition, 1-5 June 2007,
Palermo, Italy
Seismic scattering and absorption mapping from intermediate-depth earthquakes reveals complex tectonic interactions acting in the Vrancea region and surroundings (Romania)
The present study was performed during a stay at the University of Münster financed by a grant awarded by the German Academic Exchange Service (DAAD) in 2014. Data used in the present study were provided by the National Institute for Earth Physics (Romania) and processed within the National Data Centre in Magurele. Seismic Analysis Code (SAC) (Goldstein and Snoke, 2005) and GMT (Wessel et al., 2013) codes were used. We thank the College of Physical Sciences (University of Aberdeen) and the Santander Mobility Award for providing travel grant to LDS to complete this manuscript. We are grateful as well to the anonymous reviewer for his useful remarks which helped us to improve the paper.Peer reviewedPostprin
Space-weighted seismic attenuation mapping of the aseismic source of Campi Flegrei 1983-84 unrest
Peer reviewedPublisher PD
Realistic continuous-variable quantum teleportation with non-Gaussian resources
We present a comprehensive investigation of nonideal continuous-variable
quantum teleportation implemented with entangled non-Gaussian resources. We
discuss in a unified framework the main decoherence mechanisms, including
imperfect Bell measurements and propagation of optical fields in lossy fibers,
applying the formalism of the characteristic function. By exploiting
appropriate displacement strategies, we compute analytically the success
probability of teleportation for input coherent states, and two classes of
non-Gaussian entangled resources: Two-mode squeezed Bell-like states (that
include as particular cases photon-added and photon-subtracted de-Gaussified
states), and two-mode squeezed cat-like states. We discuss the optimization
procedure on the free parameters of the non-Gaussian resources at fixed values
of the squeezing and of the experimental quantities determining the
inefficiencies of the non-ideal protocol. It is found that non-Gaussian
resources enhance significantly the efficiency of teleportation and are more
robust against decoherence than the corresponding Gaussian ones. Partial
information on the alphabet of input states allows further significant
improvement in the performance of the non-ideal teleportation protocol.Comment: 14 pages, 6 figure
Continuous variable quantum teleportation with non-Gaussian resources
We investigate continuous variable quantum teleportation using non-Gaussian
states of the radiation field as entangled resources. We compare the
performance of different classes of degaussified resources, including two-mode
photon-added and two-mode photon-subtracted squeezed states. We then introduce
a class of two-mode squeezed Bell-like states with one-parameter dependence for
optimization. These states interpolate between and include as subcases
different classes of degaussified resources. We show that optimized squeezed
Bell-like resources yield a remarkable improvement in the fidelity of
teleportation both for coherent and nonclassical input states. The
investigation reveals that the optimal non-Gaussian resources for continuous
variable teleportation are those that most closely realize the simultaneous
maximization of the content of entanglement, the degree of affinity with the
two-mode squeezed vacuum and the, suitably measured, amount of non-Gaussianity.Comment: 12 pages, 12 figure
Determination of ground state properties in quantum spin systems by single qubit unitary operations and entanglement excitation energies
We introduce a method for analyzing ground state properties of quantum many
body systems, based on the characterization of separability and entanglement by
single subsystem unitary operations. We apply the method to the study of the
ground state structure of several interacting spin-1/2 models, described by
Hamiltonians with different degrees of symmetry. We show that the approach
based on single qubit unitary operations allows to introduce {\it
``entanglement excitation energies''}, a set of observables that can
characterize ground state properties, including the quantification of
single-site entanglement and the determination of quantum critical points. The
formalism allows to identify the existence and location of factorization
points, and a purely quantum {\it ``transition of entanglement''} that occurs
at the approach of factorization. This kind of quantum transition is
characterized by a diverging ratio of excitation energies associated to
single-qubit unitary operations.Comment: To appear in Phys. Rev.
Lactobacillus Cell Surface Proteins Involved in Interaction with Mucus and Extracellular Matrix Components
The gut microbiota is a complex microbial ecosystem where bacteria, through mutual interactions, cooperate in maintaining of wellbeing and health. Lactobacilli are among the most important constituents of human and animal intestinal microbiota and include many probiotic strains. Their presence ensures protection from invasion of pathogens, as well as stimulation of the immune system and protection of the intestinal flora, often exerted through the ability to interact with mucus and extracellular matrix components. The main factors responsible for mediating adhesion of pathogens and commensals to the gut are cell surface proteins that recognize host targets, as mucus layer and extracellular matrix proteins. In the last years, several adhesins have been reported to be involved in lactobacilli–host interaction often miming the same mechanism used by pathogens
Geomorphology and surface geology of Mount St. Helens volcano
Acknowledgments This work has been supported by SAGES (Scottish Alliance for Geosciences Environment and Society) Small Grants Scheme and the Jack Kleinman Grant for Volcano Research to travel to the US and perform fieldwork necessary for the realization and interpretation of the map. Thanks to the Associate Editor, Prof. Knight and the reviewers Dr. Heike Apps, Mr. Adolfo Quesada and Dr. Guido Ventura for their constructive comments and suggestions. Thanks to Alexa Van Eaton, J. J. Major and R. Waitt for their suggestions and Corrado Palucci for fieldwork assistance.Peer reviewedPublisher PD
Re-calibration of the magnitude scales at Campi Flegrei, Italy, on the basis of measured path and site and transfer functions
The quantification of the seismic energy of earthquakes occurring in volcanic regions is of great importance in order to better understand the dynamics of the volcano. The amount of the released energy and its variation during seismic crises can be considered as an indicator of the source processes acting inside the volcano. In this context, the effect of the propagation in attenuative media should be considered to correct for path effects and to properly estimate the seismic energy released at the source. Moreover, in order to allow a comparison with the dynamic processes occurring in different volcanic areas, the use of magnitude scales as homogeneous as possible is strongly recommended,
In this framework, new duration-based Local (Ml) and Moment (Mw) magnitude scales are obtained for the Campi Flegrei area (southern Italy), by analysing a data-set of local volcano-tectonic earthquakes. First the S-wave quality factor for the investigated area was experimentally calculated and then the distance-correction curve, logA0(r), to be used in the Richter formula Ml = logAmax − logA0(r), was numerically estimated by measuring the attenuation properties and hence propagating a synthetic S-wave-packet in the earth medium. The Local magnitude scale was normalized in order to fit the Richter formula valid for Southern California at a distance of 10 km. Ml magnitude was estimated by synthesizing Wood-Anderson seismograms and measuring the maximum amplitude. For the same data-set, Moment magnitude from S-wave distance and site corrected displacement spectra was obtained. Comparisons between Local and Moment magnitudes determined in the present paper, and the old Duration magnitude (Md) routinely used at the Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Vesuviano are presented. Moreover, relationships between Ml and Mw calculated for two reference sites are also derived
3-D attenuation image of fluid storage and tectonic interactions across the Pollino fault network
The Pollino range is a region of slow deformation where earthquakes generally nucleate on low-angle normal faults. Recent studies have mapped fault structures and identified fluid-related dynamics responsible for historical and recent seismicity in the area. Here, we apply the coda-normalization method at multiple frequencies and scales to image the 3-D P-wave attenuation (QP) properties of its slowly deforming fault network. The wide-scale average attenuation properties of the Pollino range are typical for a stable continental block, with a dependence of QP on frequency of . Using only waveforms comprised in the area of seismic swarms, the dependence of attenuation on frequency increases [], as expected when targeting seismically active faults. A shallow very-low-attenuation anomaly (max depth of 4-5 km) caps the seismicity recorded within the western cluster 1 of the Pollino seismic sequence (2012, maximum magnitude Mw = 5.1). High-attenuation volumes below this anomaly are likely related to fluid storage and comprise the western and northern portions of cluster 1 and the Mercure basin. These anomalies are constrained to the NW by a sharp low-attenuation interface, corresponding to the transition towards the eastern unit of the Apennine Platform under the Lauria mountains. The low-seismicity volume between cluster 1 and cluster 2 (maximum magnitude Mw = 4.3, east of the primary) shows diffuse low-to-average attenuation features. There is no clear indication of fluid-filled pathways between the two clusters resolvable at our resolution. In this volume, the attenuation values are anyway lower than in recognized low-attenuation blocks, like the Lauria Mountain and Pollino Range. As the volume develops in a region marked at surface by small-scale cross-faulting, it suggests no actual barrier between clusters, more likely a system of small locked fault patches that can break in the future. Our model loses resolution at depth, but it can still resolve a 5-to-15-km-deep high-attenuation anomaly that underlies the Castrovillari basin. This anomaly is an ideal deep source for the SE-to-NW migration of historical seismicity. Our novel deep structural maps support the hypothesis that the Pollino sequence has been caused by a mechanism of deep and lateral fluid-induced migration
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