Quantum key distribution session with 16-dimensional photonic states

The secure transfer of information is an important problem in modern telecommunications. Quantum key distribution (QKD) provides a solution to this problem by using individual quantum systems to generate correlated bits between remote parties, that can be used to extract a secret key. QKD with D-dimensional quantum channels provides security advantages that grow with increasing D. However, the vast majority of QKD implementations has been restricted to two dimensions. Here we demonstrate the feasibility of using higher dimensions for real-world quantum cryptography by performing, for the first time, a fully automated QKD session based on the BB84 protocol with 16-dimensional quantum states. Information is encoded in the single-photon transverse momentum and the required states are dynamically generated with programmable spatial light modulators. Our setup paves the way for future developments in the field of experimental high-dimensional QKD.Comment: 8 pages, 3 figure

Long-Term Neuroadaptations Produced by Withdrawal from Repeated Cocaine Treatment: Role of Dopaminergic Receptors in Modulating Cortical Excitability

Dopamine (DA) modulates neuronal activity in the prefrontal cortex (PFC) and is necessary for optimal cognitive function. Dopamine transmission in the PFC is also important for the behavioral adaptations produced by repeated exposure to cocaine. Therefore, we investigated the effects of repeated cocaine treatment followed by withdrawal (2– 4 weeks) on the responsivity of cortical cells to electrical stimulation of the ventral tegmental area (VTA) and to systemic administration of DA D1 or D2 receptor antagonists. Cortical cells in cocaine- and saline-treated animals exhibited a similar decrease in excitability after the administration of D1 receptor antagonists. In contrast, cortical neurons from cocaine-treated rats exhibited a lack of D2-mediated regulation relative to saline rats. Furthermore, in contrast to saline-treated animals, VTA stimulation did not increase cortical excitability in the cocaine group. These data suggest that withdrawal from repeated cocaine administration elicits some long-term neuroadaptations in the PFC, including (1) reduced D2-mediated regulation of cortical excitability, (2) reduced responsivity of cortical cells to phasic increases in DA, and (3) a trend toward an overall decrease in excitability of PFC neurons

Spin Josephson effect in ferromagnet/ferromagnet tunnel junctions

We consider the tunnel spin current between two ferromagnetic metals from a perspective similar to the one used in superconductor/superconductor tunnel junctions. We use fundamental arguments to derive a Josephson-like spin tunnel current $I_J^{\rm spin}\propto\sin(\theta_1-\theta_2)$. Here the phases are associated with the planar contribution to the magnetization, $\sim e^{i\theta}$. The crucial step in our analysis is the fact that the $z$-component of the spin is canonically conjugate to the phase of the planar contribution: $[\theta,S^z]=i$. This is analogous to the commutation relation $[\phi,N]=i$ in superconductors, where $\phi$ is the phase associated to the superconducting order parameter and $N$ is the Cooper pair number operator. We briefly discuss the experimental consequences of our theoretical analysis.Comment: LaTex, seven pages, no figures; version to appear in Europhys. Lett.; in order to make room for a more extended microscopic analysis, the phenomenological discussion contained in v2 was remove

Seleção assistida com uso de marcador molecular para resistência a potyvírus em pimentão.

O objetivo deste trabalho foi determinar a presença do alelo Pvr4, que confere resistência contra o PepYMV (Pepper yellow mosaic virus), em genótipos de pimentão comunmente encontrados no mercado brasileiro, com uso de um marcador molecular codominante tipo CAPS. A resistência ao PepYMV, nos genótipos CM?334?INRA, Myr?29 e em genótipos derivados do híbrido comercial Mônica?R, foi detectada como associada à banda de 444 pb, ligada ao alelo de resistência Pvr4. As plantas resistentes homozigotas (pvr4/pvr4) mostraram uma banda de 444 pb, as suscetíveis (Pvr4+/Pvr4+) uma banda de 458 pb e as resistentes heterozigotas (Pvr4+/Pvr4) mostraram as duas bandas. No entanto, no acesso resistente CM?334?UFV, nos híbridos Magali?R e Martha?R, assim como em populações derivadas desse acesso e desses híbridos, a resistência ao PepYMV não esteve associada ao marcador CAPS. O acesso CM?334?UFV ('Criollo de Morelos?334', de Viçosa, MG) distinguiu-se do CM?334?INRA ('Criollo de Morelos?334', da França); embora ambos os acessos tenham sido resistentes ao PepYMV, apenas em CM?334?INRA foi encontrada a associação da resistência com a banda de 444 pb

A higher quantum bound for the V\'ertesi-Bene-Bell-inequality and the role of POVMs regarding its threshold detection efficiency

Recently, V\'{e}rtesi and Bene [Phys. Rev. A. {\bf 82}, 062115 (2010)] derived a two-qubit Bell inequality, $I_{CH3}$, which they show to be maximally violated only when more general positive operator valued measures (POVMs) are used instead of the usual von Neumann measurements. Here we consider a general parametrization for the three-element-POVM involved in the Bell test and obtain a higher quantum bound for the $I_{CH3}$-inequality. With a higher quantum bound for $I_{CH3}$, we investigate if there is an experimental setup that can be used for observing that POVMs give higher violations in Bell tests based on this inequality. We analyze the maximum errors supported by the inequality to identify a source of entangled photons that can be used for the test. Then, we study if POVMs are also relevant in the more realistic case that partially entangled states are used in the experiment. Finally, we investigate which are the required efficiencies of the $I_{CH3}$-inequality, and the type of measurements involved, for closing the detection loophole. We obtain that POVMs allow for the lowest threshold detection efficiency, and that it is comparable to the minimal (in the case of two-qubits) required detection efficiency of the Clauser-Horne-Bell-inequality.Comment: 11 Pages, 16 Figure

Reproductive performance and reconception of Nellore cows according to their pure- or cross-bred calves.

The objective of the present research was to evaluate the effect of a calf?s genetic group on the productive and reproductive efficiency of its Nellore dam. Fixed-time artificial insemination was applied to 800 cows using semen extracted from Nellore, Simmental and Angus Red bulls. Four hundred eleven cows calved, producing 119 Nellore, 103 ½Simmental?½Nellore and 189 ½Nellore?½Angus Red calves. The second mating period, which paired Nellore cows with Simmental bulls, was initiated 10 days after parturitions began and lasted for 5 months. Based on the two successive parturitions, the cumulative parturition rate for calving periods of 3, 4 and 5 months was calculated. Although no significant difference was observed for birth weight among the genetic groups, cross-bred calves weighed, on average, 10% more than did pure-bred calves at the age of 205 days. Nellore dams experienced a gestation period that was 7 days longer than did the cross-bred dams, and the former showed a higher parturition rate at 90 and 120 days of the calving season, but not at 150 days (calving rates of 80.6, 76.4 and 76.2% for mothers of Nellore, ½Nellore?½Angus Red and ½Nellore?½Simmental, respectively, p > 0.05). At 90 and 120 days, Nellore dams produced more kg of calf per mated dam. In conclusion, in a short breeding season, Nellore dams nursing pure-bred Nellore calves were found to have a higher biological efficiency compared with Nellore dams nursing cross-bred calves

Optical Bell-state analysis in the coincidence basis

Many quantum information protocols require a Bell-state measurement of entangled systems. Most optical Bell-state measurements utilize two-photon interference at a beam splitter. By creating polarization-entangled photons with spontaneous parametric down-conversion using a first-order Hermite-Gaussian pump beam, we invert the usual interference behavior and perform an incomplete Bell-state measurement in the coincidence basis. We discuss the possibility of a complete Bell-state measurement in the coincidence basis using hyperentangled states [Phys. Rev. A, \textbf{58}, R2623 (1998)].Comment: 5 pages, 5 figure