Controlled Dephasing of Electrons by Non-Gaussian Shot Noise

In a 'controlled dephasing' experiment [1-3], an interferometer loses its coherence due to entanglement with a controlled quantum system ('which path' detector). In experiments that were conducted thus far in mesoscopic systems only partial dephasing was achieved. This was due to weak interactions between many detector electrons and the interfering electron, resulting in a Gaussian phase randomizing process [4-10]. Here, we report the opposite extreme: a complete destruction of the interference via strong phase randomization only by a few electrons in the detector. The realization was based on interfering edge channels (in the integer quantum Hall effect regime, filling factor 2) in a Mach-Zehnder electronic interferometer, with an inner edge channel serving as a detector. Unexpectedly, the visibility quenched in a periodic lobe-type form as the detector current increased; namely, it periodically decreased as the detector current, and thus the detector's efficiency, increased. Moreover, the visibility had a V-shape dependence on the partitioning of the detector current, and not the expected dependence on the second moment of the shot noise, T(1-T), with T the partitioning. We ascribe these unexpected features to the strong detector-interferometer coupling, allowing only 1-3 electrons in the detector to fully dephase the interfering electron. Consequently, in this work we explored the non-Gaussian nature of noise [11], namely, the direct effect of the shot noise full counting statistics [12-15].Comment: 14 pages, 4 figure

Non-Equilibrium Edge Channel Spectroscopy in the Integer Quantum Hall Regime

Heat transport has large potentialities to unveil new physics in mesoscopic systems. A striking illustration is the integer quantum Hall regime, where the robustness of Hall currents limits information accessible from charge transport. Consequently, the gapless edge excitations are incompletely understood. The effective edge states theory describes them as prototypal one-dimensional chiral fermions - a simple picture that explains a large body of observations and calls for quantum information experiments with quantum point contacts in the role of beam splitters. However, it is in ostensible disagreement with the prevailing theoretical framework that predicts, in most situations, additional gapless edge modes. Here, we present a setup which gives access to the energy distribution, and consequently to the energy current, in an edge channel brought out-of-equilibrium. This provides a stringent test of whether the additional states capture part of the injected energy. Our results show it is not the case and thereby demonstrate regarding energy transport, the quantum optics analogy of quantum point contacts and beam splitters. Beyond the quantum Hall regime, this novel spectroscopy technique opens a new window for heat transport and out-of-equilibrium experiments.Comment: 13 pages including supplementary information, Nature Physics in prin

New results on solar neutrino fluxes from 192 days of Borexino data

We report the direct measurement of the ^7Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV ^7Be neutrinos is 49+-3(stat)+-4(syst) counts/(day * 100ton). The hypothesis of no oscillation for ^7Be solar neutrinos is inconsistent with our measurement at the 4sigma level. Our result is the first direct measurement of the survival probability for solar nu_e in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of ^7Be, pp, and CNO solar nu_e, and the limit on the magnetic moment of neutrinos

The Borexino detector at the Laboratori Nazionali del Gran Sasso

Borexino, a large volume detector for low energy neutrino spectroscopy, is currently running underground at the Laboratori Nazionali del Gran Sasso, Italy. The main goal of the experiment is the real-time measurement of sub MeV solar neutrinos, and particularly of the mono energetic (862 keV) Be7 electron capture neutrinos, via neutrino-electron scattering in an ultra-pure liquid scintillator. This paper is mostly devoted to the description of the detector structure, the photomultipliers, the electronics, and the trigger and calibration systems. The real performance of the detector, which always meets, and sometimes exceeds, design expectations, is also shown. Some important aspects of the Borexino project, i.e. the fluid handling plants, the purification techniques and the filling procedures, are not covered in this paper and are, or will be, published elsewhere (see Introduction and Bibliography).Comment: 37 pages, 43 figures, to be submitted to NI

Manovacuometria realizada por meio de traqueias de diferentes comprimentos

Manovacuometry is a simple, fast, and non-invasive test, with maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) obtained to assist respiratory muscle assessment. Currently, there is a wide variety of models and brands of manovacuometers with different trachea diameters and lengths. However, the interference of these models in the measurements obtained by these equipments needs to be investigated. Thus, this study mainly aimed to verify the influence of tracheal length on maximal respiratory pressures (MRP), obtained by an analog manovacuometer, in healthy individuals. Our secondary objective was to verify the correlation between measurements. Fifty individuals, aged 18 to 30, of both sexes, were evaluated by spirometry and manovacuometry. MIP and MEP were performed using tracheas with same internal diameter (0.5 cm) and 30 cm, 60 cm, and 90 cm length. Significantly lower MIP values were observed when comparing a 90 cm trachea to 30 and 60 cm tracheas (Friedman’s ANOVA test and Wilcoxon test with Bonferroni adjustment). Tracheas with 30, 60, and 90 cm length and same diameter did not affect MIP and MEP values, except the 90 cm trachea for MIP values, which may interfere in the physical therapy clinical practice. Further studies are required to analyze the need for standardizing the trachea length used in manovacuometers.La manovacuometría es una prueba sencilla, rápida y no invasiva por la cual se obtienen la presión inspiratoria máxima (PImax) y la presión espiratoria máxima (PEmax), con el objetivo de ayudar en el examen muscular respiratorio. Hoy día se encuentran una gran variedad de modelos y marcas de manovacuometros, con diferentes diámetros y longitudes de las tráqueas, pero hacen falta estudios sobre la interferencia de estos modelos en las mediciones por este instrumento. En este texto se propone examinar en sujetos sanos, en primer lugar, la influencia en la longitud de las tráqueas en las presiones respiratorias máximas, obtenidas por manovacuometros analógicos, y en segundo lugar comprobar la existencia de correlación entre las mediciones. Se evaluaron a cincuenta sujetos entre 18 y 30 años de edad, tanto varones como mujeres, empleando la espirometría y la manovacuometría. Se midió la PImax y la PEmax empleando tráqueas de mismo diámetro interno (0,5 cm) y con longitudes de 30, 60 e 90 cm. Se observaron valores significativamente menores de PImax con la tráquea de longitud de 90 cm en comparación con las PImax con las tráqueas de 30 y 60 cm (prueba de Friedman’s ANOVA, la de Wilcoxon con ajustes de Bonferroni). Las tráqueas de 30, 60 y 90 cm de longitud y mismo diámetro no influyeron en los valores de la PEmax y de la PImax, con excepción de la tráquea de 90 cm en los valores de la PImax, lo que puede interferir la práctica clínica fisioterapéutica. Se necesitan más estudios para evaluar la necesidad de estándares de la longitud de tráqueas empleadas en manovacuometros.A manovacuometria é um teste simples, rápido e não invasivo por meio do qual a pressão inspiratória máxima (PImáx) e a pressão expiratória máxima (PEmáx) são obtidas, a fim de auxiliar na avaliação muscular respiratória. Atualmente, há grande variedade de modelos e marcas de manovacuômetros, com diferentes diâmetros e comprimentos de traqueias, no entanto, a interferência desses modelos nas medidas obtidas por esses equipamentos necessita de investigação. Desta forma, o objetivo primário deste estudo foi verificar a influência do comprimento de traqueias nas pressões respiratórias máximas, obtidas por meio de manovacuômetro analógico, em indivíduos saudáveis e, secundariamente, se há correlação entre as medidas. Foram avaliados 50 indivíduos, de 18 a 30 anos, de ambos os sexos, por meio da espirometria e manovacuometria. As PImáx e PEmáx foram realizadas com uso de traqueias de mesmo diâmetro interno (0,5 cm) e comprimentos de 30, 60 e 90 cm. Foram observados valores significativamente menores de PImáx obtidos com a traqueia de comprimento de 90 cm comparados às PImáx obtidas com as traqueias de 30 e 60 cm (teste de Friedman’s ANOVA com teste de Wilcoxon com ajuste de Bonferroni). As traqueias de 30, 60 e 90 cm de comprimento e mesmo diâmetro não influenciaram os valores de PEmáx e PImáx, exceto a traqueia de 90 cm para os valores de PImáx, o que pode interferir na prática clínica fisioterapêutica. Novos estudos são necessários para analisar a necessidade de padronização do comprimento da traqueia utilizada em manovacuômetros

Electrons surfing on a sound wave as a platform for quantum optics with flying electrons

Electrons in a metal are indistinguishable particles that strongly interact with other electrons and their environment. Isolating and detecting a single flying electron after propagation to perform quantum optics like experiments at the single electron level is therefore a challenging task. Up to date, only few experiments have been performed in a high mobility two-dimensional electron gas where the electron propagates almost ballistically. Flying electrons were detected via the current generated by an ensemble of electrons and electron correlations were encrypted in the current noise. Here we demonstrate the experimental realisation of high efficiency single electron source and single electron detector for a quantum medium where a single electron is propagating isolated from the other electrons through a one-dimensional channel. The moving potential is excited by a surface acoustic wave, which carries the single electron along the 1D-channel at a speed of 3\mum/ns. When such a quantum channel is placed between two quantum dots, a single electron can be transported from one quantum dot to the other, which is several micrometres apart, with a quantum efficiency of emission and detection of 96% and 92%, respectively. Furthermore, the transfer of the electron can be triggered on a timescale shorter than the coherence time T2* of GaAs spin qubits6. Our work opens new avenues to study the teleportation of a single electron spin and the distant interaction between spatially separated qubits in a condensed matter system.Comment: Total 25 pages. 12 pages main text, 4 figures, 5 pages supplementary materia

Differential expression of 12 histone deacetylase (HDAC) genes in astrocytomas and normal brain tissue: class II and IV are hypoexpressed in glioblastomas

<p>Abstract</p> <p>Background</p> <p>Glioblastoma is the most lethal primary malignant brain tumor. Although considerable progress has been made in the treatment of this aggressive tumor, the clinical outcome for patients remains poor. Histone deacetylases (HDACs) are recognized as promising targets for cancer treatment. In the past several years, HDAC inhibitors (HDACis) have been used as radiosensitizers in glioblastoma treatment. However, no study has demonstrated the status of global <it>HDAC </it>expression in gliomas and its possible correlation to the use of HDACis. The purpose of this study was to evaluate and compare mRNA and protein levels of class I, II and IV of HDACs in low grade and high grade astrocytomas and normal brain tissue and to correlate the findings with the malignancy in astrocytomas.</p> <p>Methods</p> <p>Forty-three microdissected patient tumor samples were evaluated. The histopathologic diagnoses were 20 low-grade gliomas (13 grade I and 7 grade II) and 23 high-grade gliomas (5 grade III and 18 glioblastomas). Eleven normal cerebral tissue samples were also analyzed (54 total samples analyzed). mRNA expression of class I, II, and IV <it>HDACs </it>was studied by quantitative real-time polymerase chain reaction and normalized to the housekeeping gene <it>β-glucuronidase</it>. Protein levels were evaluated by western blotting.</p> <p>Results</p> <p>We found that mRNA levels of class II and IV <it>HDACs </it>were downregulated in glioblastomas compared to low-grade astrocytomas and normal brain tissue (7 in 8 genes, <it>p </it>< 0.05). The protein levels of class II HDAC9 were also lower in high-grade astrocytomas than in low-grade astrocytomas and normal brain tissue. Additionally, we found that histone H3 (but not histone H4) was more acetylated in glioblastomas than normal brain tissue.</p> <p>Conclusion</p> <p>Our study establishes a negative correlation between <it>HDAC </it>gene expression and the glioma grade suggesting that class II and IV <it>HDACs </it>might play an important role in glioma malignancy. Evaluation of histone acetylation levels showed that histone H3 is more acetylated in glioblastomas than normal brain tissue confirming the downregulation of <it>HDAC </it>mRNA in glioblastomas.</p

Measurements of extremely low radioactivity levels in BOREXINO

The techniques researched, developed and applied towards the measurement of radioisotope concentrations at ultra-low levels in the real-time solar neutrino experiment BOREXINO at Gran Sasso are presented and illustrated with specific results of widespread interest. We report the use of low-level germanium gamma spectrometry, low-level miniaturized gas proportional counters and low background scintillation detectors developed in solar neutrino research. Each now sets records in its field. We additionally describe our techniques of radiochemical ultra-pure, few atom manipulations and extractions. Forefront measurements also result from the powerful combination of neutron activation and low-level counting. Finally, with our techniques and commercially available mass spectrometry and atomic absorption spectroscopy, new low-level detection limits for isotopes of interest are obtained.Comment: 27 pages, 5 figures. Submitted to Astroparticle Physics (17 Sep 2001). Spokesperson of the Borexino Collaboration: G. Bellini. Corresponding author: W. Hampe