357 research outputs found
Beating the channel capacity limit for linear photonic superdense coding
Dense coding is arguably the protocol that launched the field of quantum
communication. Today, however, more than a decade after its initial
experimental realization, the channel capacity remains fundamentally limited as
conceived for photons using linear elements. Bob can only send to Alice three
of four potential messages owing to the impossibility of carrying out the
deterministic discrimination of all four Bell states with linear optics,
reducing the attainable channel capacity from 2 to log_2 3 \approx 1.585 bits.
However, entanglement in an extra degree of freedom enables the complete and
deterministic discrimination of all Bell states. Using pairs of photons
simultaneously entangled in spin and orbital angular momentum, we demonstrate
the quantum advantage of the ancillary entanglement. In particular, we describe
a dense-coding experiment with the largest reported channel capacity and, to
our knowledge, the first to break the conventional linear-optics threshold. Our
encoding is suited for quantum communication without alignment and satellite
communication.Comment: Letter: 6 pages, 4 figures. Supplementary Information: 4 pages, 1
figur
Experimental demonstration of a hyper-entangled ten-qubit Schr\"odinger cat state
Coherent manipulation of an increasing number of qubits for the generation of
entangled states has been an important goal and benchmark in the emerging field
of quantum information science. The multiparticle entangled states serve as
physical resources for measurement-based quantum computing and high-precision
quantum metrology. However, their experimental preparation has proved extremely
challenging. To date, entangled states up to six, eight atoms, or six photonic
qubits have been demonstrated. Here, by exploiting both the photons'
polarization and momentum degrees of freedom, we report the creation of
hyper-entangled six-, eight-, and ten-qubit Schr\"odinger cat states. We
characterize the cat states by evaluating their fidelities and detecting the
presence of genuine multi-partite entanglement. Small modifications of the
experimental setup will allow the generation of various graph states up to ten
qubits. Our method provides a shortcut to expand the effective Hilbert space,
opening up interesting applications such as quantum-enhanced super-resolving
phase measurement, graph-state generation for anyonic simulation and
topological error correction, and novel tests of nonlocality with
hyper-entanglement.Comment: 11 pages, 5 figures, comments welcom
Point process time–frequency analysis of dynamic respiratory patterns during meditation practice
Respiratory sinus arrhythmia (RSA) is largely mediated by the autonomic nervous system through its modulating influence on the heart beats. We propose a robust algorithm for quantifying instantaneous RSA as applied to heart beat intervals and respiratory recordings under dynamic breathing patterns. The blood volume pressure-derived heart beat series (pulse intervals, PIs) are modeled as an inverse Gaussian point process, with the instantaneous mean PI modeled as a bivariate regression incorporating both past PIs and respiration values observed at the beats. A point process maximum likelihood algorithm is used to estimate the model parameters, and instantaneous RSA is estimated via a frequency domain transfer function evaluated at instantaneous respiratory frequency where high coherence between respiration and PIs is observed. The model is statistically validated using Kolmogorov–Smirnov goodness-of-fit analysis, as well as independence tests. The algorithm is applied to subjects engaged in meditative practice, with distinctive dynamics in the respiration patterns elicited as a result. The presented analysis confirms the ability of the algorithm to track important changes in cardiorespiratory interactions elicited during meditation, otherwise not evidenced in control resting states, reporting statistically significant increase in RSA gain as measured by our paradigm.National Institutes of Health (U.S.) (Grant R01-HL084502)National Institutes of Health (U.S.) (Grant R01-DA015644)National Institutes of Health (U.S.) (Grant DP1-OD003646)National Institutes of Health (U.S.) (Grant K01-AT00694-01
Scalar geometry and masses in Calabi-Yau string models
We study the geometry of the scalar manifolds emerging in the no-scale sector
of Kahler moduli and matter fields in generic Calabi-Yau string
compactifications, and describe its implications on scalar masses. We consider
both heterotic and orientifold models and compare their characteristics. We
start from a general formula for the Kahler potential as a function of the
topological compactification data and study the structure of the curvature
tensor. We then determine the conditions for the space to be symmetric and show
that whenever this is the case the heterotic and the orientifold models give
the same scalar manifold. We finally study the structure of scalar masses in
this type of geometries, assuming that a generic superpotential triggers
spontaneous supersymmetry breaking. We show in particular that their behavior
crucially depends on the parameters controlling the departure of the geometry
from the coset situation. We first investigate the average sGoldstino mass in
the hidden sector and its sign, and study the implications on vacuum
metastability and the mass of the lightest scalar. We next examine the soft
scalar masses in the visible sector and their flavor structure, and study the
possibility of realizing a mild form of sequestering relying on a global
symmetry.Comment: 36 pages, no figure
Observation of eight-photon entanglement
Using ultra-bright sources of pure-state entangled photons from parametric
down conversion, an eight-photon interferometer and post-selection detection,
we demonstrate the ability to experimentally manipulate eight individual
photons and report the creation of an eight-photon Schr\"odinger cat state with
an observed fidelity of .Comment: 6 pages, 4 figure
Twenty Years of SUGRA
A brief review is given of the developments of mSUGRA and its extensions
since the formulation of these models in 1982. Future directions and prospects
are also discussed.Comment: Invited talk at the International Conference BEYOND-2003, Schloss
Ringberg, Germany, June 10-14, 2003; 21 pages, Late
Prospective study of asbestos-related diseases incidence cases in primary health care in an area of Barcelona province
<p>Abstract</p> <p>Background</p> <p>Asbestos related diseases include a number of conditions due to inhalation of asbestos fibres at work, at home or in the environment, such as pleural mesothelioma, asbestosis and calcified pleural plaques. Few epidemiological studies have established the incidence of asbestos related diseases in our area. The present proposal is based on a retrospective study externally funded in 2005 that is currently taking place in the same area and largely carried out by the same research team.</p> <p>The aim of the study is to achieve a comprehensive and coordinated detection of all new cases of Asbestos Related Diseases presenting to primary care practitioners.</p> <p>Methods/design</p> <p>This is a multicentre, multidisciplinary and pluri-institutional prospective study.</p> <p><b>Setting</b></p> <p>12 municipalities in the Barcelona province within the catchment area of the health facilities that participate in the study.</p> <p><b>Sample</b></p> <p>This is a population based study, of all patients presenting with diseases caused by asbestos in the study area.</p> <p><b>Measurements</b></p> <p>A clinical and epidemiological questionnaire will be filled in by the trained researchers after interviewing the patients and examining their clinical reports.</p> <p>Discussion</p> <p>Data on the incidence of the different Asbestos Related Diseases in this area will be obtained and the most plausible exposure source and space-time-patient profile will be described. The study will also improve the standardization of patient management, the coordination between health care institutions and the development of preventive activities related with asbestos exposure and disease.</p
Free-Space distribution of entanglement and single photons over 144 km
Quantum Entanglement is the essence of quantum physics and inspires
fundamental questions about the principles of nature. Moreover it is also the
basis for emerging technologies of quantum information processing such as
quantum cryptography, quantum teleportation and quantum computation. Bell's
discovery, that correlations measured on entangled quantum systems are at
variance with a local realistic picture led to a flurry of experiments
confirming the quantum predictions. However, it is still experimentally
undecided whether quantum entanglement can survive global distances, as
predicted by quantum theory. Here we report the violation of the
Clauser-Horne-Shimony-Holt (CHSH) inequality measured by two observers
separated by 144 km between the Canary Islands of La Palma and Tenerife via an
optical free-space link using the Optical Ground Station (OGS) of the European
Space Agency (ESA). Furthermore we used the entangled pairs to generate a
quantum cryptographic key under experimental conditions and constraints
characteristic for a Space-to-ground experiment. The distance in our experiment
exceeds all previous free-space experiments by more than one order of magnitude
and exploits the limit for ground-based free-space communication; significantly
longer distances can only be reached using air- or space-based platforms. The
range achieved thereby demonstrates the feasibility of quantum communication in
space, involving satellites or the International Space Station (ISS).Comment: 10 pages including 2 figures and 1 table, Corrected typo
Modulation of the Akt/Ras/Raf/MEK/ERK pathway by A3 adenosine receptor
Downstream A3 receptor signalling plays an important role in the regulation of cell death and proliferation. Therefore, it is important to determine the molecular pathways involved through A3 receptor stimulation. The phosphatidylinositide-3-OH kinase (PI3K)/Akt and the Raf/mitogen-activated protein kinase (MAPK/ERK) kinase (MEK)/mitogen-activated protein kinase (MAPK) pathways have central roles in the regulation of cell survival and proliferation. The crosstalk between these two pathways has also been investigated. The focus of this review centres on downstream mediators of A3 adenosine receptor signalling
Progestin Receptor-Mediated Reduction of Anxiety-Like Behavior in Male Rats
BACKGROUND: It is well known progesterone can have anxiolytic-like effects in animals in a number of different behavioral testing paradigms. Although progesterone is known to influence physiology and behavior by binding to classical intracellular progestin receptors, progesterone's anxiety reducing effects have solely been attributed to its rapid non-genomic effects at the GABA A receptor. This modulation occurs following the bioconversion of progesterone to allopregnanolone. Seemingly paradoxical results from some studies suggested that the function of progesterone to reduce anxiety-like behavior may not be entirely clear; therefore, we hypothesized that progesterone might also act upon progestin receptors to regulate anxiety. METHODOLOGY/PRINCIPAL FINDINGS: To test this, we examined the anxiolytic-like effects of progesterone in male rats using the elevated plus maze, a validated test of anxiety, and the light/dark chamber in the presence or absence of a progestin receptor antagonist, RU 486. Here we present evidence suggesting that the anxiolytic-like effects of progesterone in male rats can be mediated, in part, by progestin receptors, as these effects are blocked by prior treatment with a progestin receptor antagonist. CONCLUSION/SIGNIFICANCE: This indicates that progesterone can act upon progestin receptors to regulate anxiety-like behavior in the male rat brain
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