Qubit-portraits of qudit states and quantum correlations

The machinery of qubit-portraits of qudit states, recently presented, is consider here in more details in order to characterize the presence of quantum correlations in bipartite qudit states. In the tomographic representation of quantum mechanics, Bell-like inequalities are interpreted as peculiar properties of a family of classical joint probability distributions which describe the quantum state of two qudits. By means of the qubit-portraits machinery a semigroup of stochastic matrices can be associated to a given quantum state. The violation of the CHSH inequalities is discussed in this framework with some examples, we found that quantum correlations in qutrit isotropic states can be detected by the suggested method while it cannot in the case of qutrit Werner states.Comment: 12 pages, 4 figure

Robustness against parametric noise of non ideal holonomic gates

Holonomic gates for quantum computation are commonly considered to be robust against certain kinds of parametric noise, the very motivation of this robustness being the geometric character of the transformation achieved in the adiabatic limit. On the other hand, the effects of decoherence are expected to become more and more relevant when the adiabatic limit is approached. Starting from the system described by Florio et al. [Phys. Rev. A 73, 022327 (2006)], here we discuss the behavior of non ideal holonomic gates at finite operational time, i.e., far before the adiabatic limit is reached. We have considered several models of parametric noise and studied the robustness of finite time gates. The obtained results suggest that the finite time gates present some effects of cancellation of the perturbations introduced by the noise which mimic the geometrical cancellation effect of standard holonomic gates. Nevertheless, a careful analysis of the results leads to the conclusion that these effects are related to a dynamical instead of geometrical feature.Comment: 8 pages, 8 figures, several changes made, accepted for publication on Phys. Rev.

Bipartite quantum systems: on the realignment criterion and beyond

Inspired by the `computable cross norm' or `realignment' criterion, we propose a new point of view about the characterization of the states of bipartite quantum systems. We consider a Schmidt decomposition of a bipartite density operator. The corresponding Schmidt coefficients, or the associated symmetric polynomials, are regarded as quantities that can be used to characterize bipartite quantum states. In particular, starting from the realignment criterion, a family of necessary conditions for the separability of bipartite quantum states is derived. We conjecture that these conditions, which are weaker than the parent criterion, can be strengthened in such a way to obtain a new family of criteria that are independent of the original one. This conjecture is supported by numerical examples for the low dimensional cases. These ideas can be applied to the study of quantum channels, leading to a relation between the rate of contraction of a map and its ability to preserve entanglement.Comment: 19 pages, 4 figures, improved versio

Quantifying the Performance of Quantum Codes

We study the properties of error correcting codes for noise models in the presence of asymmetries and/or correlations by means of the entanglement fidelity and the code entropy. First, we consider a dephasing Markovian memory channel and characterize the performance of both a repetition code and an error avoiding code in terms of the entanglement fidelity. We also consider the concatenation of such codes and show that it is especially advantageous in the regime of partial correlations. Finally, we characterize the effectiveness of the codes and their concatenation by means of the code entropy and find, in particular, that the effort required for recovering such codes decreases when the error probability decreases and the memory parameter increases. Second, we consider both symmetric and asymmetric depolarizing noisy quantum memory channels and perform quantum error correction via the five qubit stabilizer code. We characterize this code by means of the entanglement fidelity and the code entropy as function of the asymmetric error probabilities and the degree of memory. Specifically, we uncover that while the asymmetry in the depolarizing errors does not affect the entanglement fidelity of the five qubit code, it becomes a relevant feature when the code entropy is used as a performance quantifier.Comment: 21 pages, 10 figure

Effect of dielectric barrier on rectification, injection and transport properties of printed organic diodes

International audienceRectification ratios of 10 5 were observed in printed organic copper/polytriarylamine (PTAA)/silver diodes with a thin insulating barrier layer at the copper/PTAA interface. To clarify the origin of the high rectification ratio in the diodes, the injection, transport and structure of the diodes with two different copper cathodes were examined using impedance spectroscopy and X-ray photoelectron spectroscopy (XPS). The impedance data confirm that the difference in diode performance arises from the copper/PTAA interface. The XPS measurements show that the copper surface in both diode structures is covered by a layer of Cu 2 O topped by an organic layer. The organic layer is thicker on one of the surfaces, which results in lower reverse currents and higher rectification ratios in the printed diodes. We suggest a model where a dipole at the dual insulating layer induces a shift in the semiconductor energy levels explaining the difference between the diodes with different cathodes

Autonomous UAV-based mapping of large-scale urban firefights

This paper describes experimental results from a live-fire data collect designed to demonstrate the ability of IR and acoustic sensing systems to detect and map high-volume gunfire events from tactical UAVs. The data collect supports an exploratory study of the FightSight concept in which an autonomous UAV-based sensor exploitation and decision support capability is being proposed to provide dynamic situational awareness for large-scale battalion-level firefights in cluttered urban environments. FightSight integrates IR imagery, acoustic data, and 3D scene context data with prior time information in a multi-level, multi-step probabilistic-based fusion process to reliably locate and map the array of urban firing events and firepower movements and trends associated with the evolving urban battlefield situation. Described here are sensor results from live-fire experiments involving simultaneous firing of multiple sub/super-sonic weapons (2-AK47, 2-M16, 1 Beretta, 1 Mortar, 1 rocket) with high optical and acoustic clutter at ranges up to 400m. Sensor-shooter-target configurations and clutter were designed to simulate UAV sensing conditions for a high-intensity firefight in an urban environment. Sensor systems evaluated were an IR bullet tracking system by Lawrence Livermore National Laboratory (LLNL) and an acoustic gunshot detection system by Planning Systems, Inc. (PSI). The results demonstrate convincingly the ability for the LLNL and PSI sensor systems to accurately detect, separate, and localize multiple shooters and the associated shot directions during a high-intensity firefight (77 rounds in 5 sec) in a high acoustic and optical clutter environment with no false alarms. Preliminary fusion processing was also examined that demonstrated an ability to distinguish co-located shooters (shooter density), range to <0.5 m accuracy at 400m, and weapon type

Quantitative 7T Phase Imaging in Premanifest Huntington Disease

BACKGROUND AND PURPOSE: In vivo MRI and postmortem neuropathological studies have demonstrated elevated iron concentration and atrophy within the striatum of patients with Huntington disease (HD), implicating neuronal loss and iron accumulation in the pathogenesis of this neurodegenerative disorder. We used 7T MRI to determine whether quantitative phase, a putative marker of these endpoints, is altered in subjects with premotor HD. MATERIALS AND METHODS: Local field shift (LFS), calculated from 7T MR phase images, was quantified in 13 subjects with premotor HD and 13 age- and gender-matched controls. All participants underwent 3T and 7T MRI, including volumetric 3T T1 and 7T gradient-recalled echo sequences. LFS maps were created from 7T phase data and registered to caudate ROIs automatically parcellated from the 3T T1 images. HD-specific neurocognitive assessment was also performed and compared to LFS. RESULTS: Subjects with premotor HD had smaller caudate nuclear volume and higher LFS than controls. A significant correlation between these measurements was not detected, and prediction accuracy for disease state improved with inclusion of both variables. A positive correlation between LFS and genetic disease burden was also found, and there was a trend towards significant correlations between LFS and neurocognitive tests of working memory and executive function. CONCLUSION: Subjects with premotor HD exhibit differences in 7T MRI phase within the caudate nuclei that correlate with genetic disease burden and trend with neurocognitive assessments. Ultra-high field MRI of quantitative phase may be a useful marker for monitoring neurodegeneration in premanifest HD

Altruism and sacrifice : mafia free gift giving in south Italy

As a social phenomenon that torments modern states, mafia receives considerable political and legal attention. The term mafia itself is often directly related to criminality and violence. Thus far violence has been employed as an analytical construct that could explain compliance with the mafia ethos. Nevertheless this schema fails to take into consideration possible discourses that make mafia tolerable. Drawing on fieldwork conducted in Reggio Calabria, South Italy, this paper explores distinctive mafia notions of giving and charity. Mafia free gifts, albeit rare, are paradoxical in the sense that through elaborate speech registers both the donor and the recipient debase the very act of gift-giving so as not to be bound in relations of reciprocity and obligation. These mafia gifts, which have so far escaped anthropological attention, are conceptualised as tropes of worldly imagining aspiring to non-worldly discourses. Status, umiltà, duty and sacrifice frame free gifting as accorded to the overt religious rhetoric of mafia hierarchy. In this paper I argue that a) free gifting embraces a series of complex non-violent discourses which relate closely to religious duty and altruism but work alongside capitalist systems b) in principal these gifts do not bind people, yet are imbued with the potential of a relation.PostprintPeer reviewe

Mapping Forbidden Emission to Structure in Self-Assembled Organic Nanoparticles

© 2018 American Chemical Society. The interplay between micromorphology and electronic properties is an important theme in organic electronic materials. Here, we show that a spirofluorene-functionalized boron-dipyrromethene (BODIPY) with an alkyl norbornyl tail self-assembles into nanoparticles with qualitatively different properties as compared to the polymerized species. Further, the nanoparticles exhibit a host of unique emissive properties, including photobrightening, a blue satellite peak, and spectral diffusion. Extensive photophysical characterization, including single-particle imaging and spectroscopy, and time-resolved fluorescence, coupled with electronic structure calculations based on an experimentally determined crystal structure, allow a mechanism to be developed. Specifically, BODIPY chromophores are observed to form quasi-two-dimensional layers, where stacking of unit cells adds either J-aggregate character or H-aggregate character depending on the direction of the stacking. Particularly strongly H-coupled domains show the rare process of emission from an upper exciton state, in violation of Kasha's rule, and result in the blue satellite peak. The spatial heterogeneity of structure thus maps onto a gradient of photophysical behavior as seen in single-particle imaging, and the temporal evolution of structure maps onto fluctuating emissive behavior, as seen in single-particle spectroscopy. Taken together, this system provides a striking example of how physical structure and electronic properties are intertwined, and a rare opportunity to use one to chart the other