Positive cross-correlations in a three-terminal quantum dot with ferromagnetic contacts

We study current fluctuations in an interacting three-terminal quantum dot with ferromagnetic leads. For appropriately polarized contacts, the transport through the dot is governed by a novel dynamical spin blockade, i.e., a spin-dependent bunching of tunneling events not present in the paramagnetic case. This leads for instance to positive zero-frequency cross-correlations of the currents in the output leads even in the absence of spin accumulation on the dot. We include the influence of spin-flip scattering and identify favorable conditions for the experimental observation of this effect with respect to polarization of the contacts and tunneling rates.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let

Description sensorielle de la carotte - recherche et mise au point d'une méthodologie

En évaluation sensorielle, la description des caractéristiques organoleptiques d\u27un produit par la méthode de profil sensoriel demande, dans un premier temps, de déterminer les descripteurs qui vont être pertinents dans la caractérisation du produit. Cet article présente les différentes étapes de mise en place d\u27une liste de descripteurs appliquée à la carotte. La carotte étant un produit consommé cru ou cuit et sous différentes formes, trois modes d\u27usage (carotte crue râpée, cuite entière, crue en rondelle...) vont être comparés, afin de déterminer quel est l\u27apport de chacune des méthodes dans la description du produit

Dephasing of qubits by transverse low-frequency noise

We analyze the dissipative dynamics of a two-level quantum system subject to low-frequency, e.g. 1/f noise, motivated by recent experiments with superconducting quantum circuits. We show that the effect of transverse linear coupling of the system to low-frequency noise is equivalent to that of quadratic longitudinal coupling. We further find the decay law of quantum coherent oscillations under the influence of both low- and high-frequency fluctuations, in particular, for the case of comparable rates of relaxation and pure dephasing

French consumer preferences reveal a potential for segmentation in carrot

Gustatory differentiation is one possible means of segmentation. Consumer preferences of carrot were studied within the framework of the CosiVeg project. The characteristics of batches offered for consumer assessment enables their preferences to be evaluated. In preparation for a hedonic test of raw grated carrots that was carried out in autumn 2011, the carrot sensory space was studied in 2010 using 48 batches that were evaluated using quantative descriptive sensory analysis. The cultivars were representative of different types, Nantais, Imperator, Flakkee, coloured carrots and genetic resources. . Significant differences were observed for all criteria, allowing varieties to be grouped based on their sensory characteristics. Texture, flavor and aroma contribute to the “identity” of carrots. Overall aroma is correlated with perceptions of bitterness, sharpness and chemical aroma. Fourteen orange carrot varieties were selected for sowing in 2011. In 2010, although maximum scores were obtained for pungent and bitter attributes, this was not the case in 2011. In spite of this, the selected batches allowed the different profiles of the sensory characteristics of the carrots to be determined. Ten batches of carrot that represented a wide range of variability were tasted by a trained panel as well as a consumer panel; the product was presented as raw grated carrot. The sensory measurements obtained were used to map preferences, underlining preferences for a carrot that is juicy, aromatic and sweet. However bitter and chemical flavour carrots were not appreciated. Three types of consumer exist each having different expectations in terms of quality. Almost 20 % of people questioned are looking for a high quality product, for 33 % of consumers carrots are a staple food and they have no specific expectations and 48 % are satisfied with the current product but are potentially interested by a product that would distinguish itself as regards to quality. It means that segmentation with a high gustatory quality will be of interest for one consumer for 5

Qualité organoleptique de la carotte : variabilité des critères sensoriels selon le type variétal

La différenciation gustative est une voie possible de segmentation. L\u27étude a porté sur la variabilité des critères sensoriels dans le matériel végétal. Trente-trois varié - tés des types Nantais, Imperator, Flakkee, de carottes de couleur et de ressources génétiques ont été caractérisées en analyse sensorielle descriptive quantitative et par des mesures physico-chimiques. Des différences significatives pour tous les critères existent et permettent de regrouper les variétés sur la base de leurs caractéristiques sensorielles. Texture, saveur et arôme contribuent à la typicité de la carotte ; l\u27arôme global est corrélé aux perceptions d\u27amer, de piquant et d\u27arôme chimique. La mesure des sucres ne permet pas d\u27évaluer la perception en bouche du sucre du fait de l\u27influence du potentiel d\u27amertume

Positive cross-correlations due to Dynamical Channel-Blockade in a three-terminal quantum dot

We investigate current fluctuations in a three-terminal quantum dot in the sequential tunneling regime. In the voltage-bias configuration chosen here, the circuit is operated like a beam splitter, i.e. one lead is used as an input and the other two as outputs. In the limit where a double occupancy of the dot is not possible, a super-Poissonian Fano factor of the current in the input lead and positive cross-correlations between the current fluctuations in the two output leads can be obtained, due to dynamical channel-blockade. When a single orbital of the dot transports current, this effect can be obtained by lifting the spin-degeneracy of the circuit with ferromagnetic leads or with a magnetic field. When several orbitals participate in the electronic conduction, lifting spin-degeneracy is not necessary. In all cases, we show that a super-Poissonian Fano factor for the input current is not equivalent to positive cross-correlations between the outputs. We identify the conditions for obtaining these two effects and discuss possible experimental realizations.Comment: 18 pages, 20 Figures, submitted to Phys. rev.

Spin-dependent boundary conditions for isotropic superconducting Green's functions

The quasiclassical theory of superconductivity provides the most successful description of diffusive heterostructures comprising superconducting elements, namely, the Usadel equations for isotropic Green's functions. Since the quasiclassical and isotropic approximations break down close to interfaces, the Usadel equations have to be supplemented with boundary conditions for isotropic Green's functions (BCIGF), which are not derivable within the quasiclassical description. For a long time, the BCIGF were available only for spin-degenerate tunnel contacts, which posed a serious limitation on the applicability of the Usadel description to modern structures containing ferromagnetic elements. In this article, we close this gap and derive spin-dependent BCIGF for a contact encompassing superconducting and ferromagnetic correlations. This finally justifies several simplified versions of the spin-dependent BCIGF, which have been used in the literature so far. In the general case, our BCIGF are valid as soon as the quasiclassical isotropic approximation can be performed. However, their use require the knowledge of the full scattering matrix of the contact, an information usually not available for realistic interfaces. In the case of a weakly polarized tunnel interface, the BCIGF can be expressed in terms of a few parameters, i.e. the tunnel conductance of the interface and five conductance-like parameters accounting for the spin-dependence of the interface scattering amplitudes. In the case of a contact with a ferromagnetic insulator, it is possible to find explicit BCIGF also for stronger polarizations. The BCIGF derived in this article are sufficienly general to describe a variety of physical situations and may serve as a basis for modelling realistic nanostructures.Comment: This paper presents an improvement of arXiv:cond-mat/0204116. The present version takes into account corrections from the erratum Phys. Rev. B 83, 139901 (2011