Dephasing of solid-state qubits at optimal points

Motivated by recent experiments with Josephson-junction circuits, we analyze the influence of various noise sources on the dynamics of two-level systems at optimal operation points where the linear coupling to low-frequency fluctuations is suppressed. We study the decoherence due to nonlinear (quadratic) coupling, focusing on the experimentally relevant 1/f and Ohmic noise power spectra. For 1/f noise strong higher-order effects influence the evolution.Comment: minor corrections and clarification

Effect of the attachment of ferromagnetic contacts on the conductivity and giant magnetoresistance of graphene nanoribbons

Carbon-based nanostructures and graphene, in particular, evoke a lot of interest as new promising materials for nanoelectronics and spintronics. One of the most important issue in this context is the impact of external electrodes on electronic properties of graphene nanoribbons (GNR). The present theoretical method is based on the tight-binding model and a modified recursive procedure for Green's functions. The results show that within the ballistic transport regime, the so called end-contacted geometry (of minimal GNR/electrode interface area), is usually more advantageous for practical applications than its side-contacted counterpart (with a larger coverage area), as far as the electrical conductivity is concerned. As regards the giant magnetoresistance coefficient, however, the situation is exactly opposite, since spin- splitting effects are more pronounced in the lower conductive side-contacted setups.Comment: 8 pages, 4 figure

Photon mediated interaction between distant quantum dot circuits

Engineering the interaction between light and matter is an important goal in the emerging field of quantum opto-electronics. Thanks to the use of cavity quantum electrodynamics architectures, one can envision a fully hybrid multiplexing of quantum conductors. Here, we use such an architecture to couple two quantum dot circuits . Our quantum dots are separated by 200 times their own size, with no direct tunnel and electrostatic couplings between them. We demonstrate their interaction, mediated by the cavity photons. This could be used to scale up quantum bit architectures based on quantum dot circuits or simulate on-chip phonon-mediated interactions between strongly correlated electrons

Modeling a Schottky-barrier carbon nanotube field-effect transistor with ferromagnetic contacts

In this study, a model of a Schottky-barrier carbon nanotube field- effect transistor (CNT-FET), with ferromagnetic contacts, has been developed. The emphasis is put on analysis of current-voltage characteristics as well as shot (and thermal) noise. The method is based on the tight-binding model and the non- equilibrium Green's function technique. The calculations show that, at room temperature, the shot noise of the CNT FET is Poissonian in the sub-threshold region, whereas in elevated gate and drain/source voltage regions the Fano factor gets strongly reduced. Moreover, transport properties strongly depend on relative magnetization orientations in the source and drain contacts. In particular, one observes quite a large tunnel magnetoresistance, whose absolute value may exceed 50%.Comment: 8 pages, 4 figure

Using Spontaneous Emission of a Qubit as a Resource for Feedback Control

Persistent control of a transmon qubit is performed by a feedback protocol based on continuous heterodyne measurement of its fluorescence. By driving the qubit and cavity with microwave signals whose amplitudes depend linearly on the instantaneous values of the quadratures of the measured fluorescence field, we show that it is possible to stabilize permanently the qubit in any targeted state. Using a Josephson mixer as a phase-preserving amplifier, it was possible to reach a total measurement efficiency $\eta$=35%, leading to a maximum of 59% of excitation and 44% of coherence for the stabilized states. The experiment demonstrates multiple-input multiple-output analog Markovian feedback in the quantum regime.Comment: Supplementary material can be found as an ancillary objec

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

Nanospintronics with carbon nanotubes

One of the actual challenges of spintronics is the realization of a spin-transistor allowing to control spin transport through an electrostatic gate. In this review, we report on different experiments which demonstrate a gate control of spin transport in a carbon nanotube connected to ferromagnetic leads. We also discuss some theoretical approaches which can be used to analyze spin transport in these systems. We emphasize the roles of the gate-tunable quasi-bound states inside the nanotube and the coherent spin-dependent scattering at the interfaces between the nanotube and its ferromagnetic contacts.Comment: 35 pages, 15 figures, some figures in gi