TY - JOUR AB - Recent experiments have shown that motion detection in Drosophila starts with splitting the visual input into two parallel channels encoding brightness increments (ON) or decrements (OFF). This suggests the existence of either two (ON-ON, OFF-OFF) or four (for all pairwise interactions) separate motion detectors. To decide between these possibilities, we stimulated flies using sequences of ON and OFF brightness pulses while recording from motion-sensitive tangential cells. We found direction-selective responses to sequences of same sign (ON-ON, OFF-OFF), but not of opposite sign (ON-OFF, OFF-ON), refuting the existence of four separate detectors. Based on further measurements, we propose a model that reproduces a variety of additional experimental data sets, including ones that were previously interpreted as support for four separate detectors. Our experiments and the derived model mark an important step in guiding further dissection of the fly motion detection circuit. AU - Eichner, Hubert AU - Maximilian Jösch AU - Schnell, Bettina AU - Reiff, Dierk F AU - Borst, Alexander ID - 1299 IS - 6 JF - Neuron TI - Internal structure of the fly elementary motion detector VL - 70 ER - TY - JOUR AB - We propose a general conjecture for the mixed Hodge polynomial of the generic character varieties of representations of the fundamental group of a Riemann surface of genus g to GLn(C) with fixed generic semisimple conjugacy classes at k punctures. This conjecture generalizes the Cauchy identity for Macdonald polynomials and is a common generalization of two formulas that we prove in this paper. The first is a formula for the E-polynomial of these character varieties which we obtain using the character table of GLn(Fq). We use this formula to compute the Euler characteristic of character varieties. The second formula gives the Poincaré polynomial of certain associated quiver varieties which we obtain using the character table of gln(Fq). In the last main result we prove that the Poincaré polynomials of the quiver varieties equal certain multiplicities in the tensor product of irreducible characters of GLn(Fq). As a consequence we find a curious connection between Kac-Moody algebras associated with comet-shaped, and typically wild, quivers and the representation theory of GLn(Fq). AU - Tamas Hausel AU - Letellier, Emmanuel AU - Rodríguez Villegas, Fernando ID - 1467 IS - 2 JF - Duke Mathematical Journal TI - Arithmetic harmonic analysis on character and quiver varieties VL - 160 ER - TY - JOUR AB - The emergence of differences in the arrangement of cells is the first step towards the establishment of many organs. Understanding this process is limited by the lack of systematic characterization of epithelial organisation. Here we apply network theory at the scale of individual cells to uncover patterns in cell-to-cell contacts that govern epithelial organisation. We provide an objective characterisation of epithelia using network representation, where cells are nodes and cell contacts are links. The features of individual cells, together with attributes of the cellular network, produce a defining signature that distinguishes epithelia from different organs, species, developmental stages and genetic conditions. The approach permits characterization, quantification and classification of normal and perturbed epithelia, and establishes a framework for understanding molecular mechanisms that underpin the architecture of complex tissues. AU - Escudero, Luis M AU - Costa, Luciano AU - Anna Kicheva AU - Briscoe, James AU - Freeman, Matthew AU - Babu, Madan M ID - 1723 IS - 1 JF - Nature Communications TI - Epithelial organisation revealed by a network of cellular contacts VL - 2 ER - TY - JOUR AB - Morphogens, such as Decapentaplegic (Dpp) in the fly imaginal discs, form graded concentration profiles that control patterning and growth of developing organs. In the imaginal discs, proliferative growth is homogeneous in space, posing the conundrum of how morphogen concentration gradients could control position-independent growth. To understand the mechanism of proliferation control by the Dpp gradient, we quantified Dpp concentration and signaling levels during wing disc growth. Both Dpp concentration and signaling gradients scale with tissue size during development. On average, cells divide when Dpp signaling levels have increased by 50%. Our observations are consistent with a growth control mechanism based on temporal changes of cellular morphogen signaling levels. For a scaling gradient, this mechanism generates position-independent growth rates. AU - Wartlick, Ortrud AU - Mumcu, Peer AU - Anna Kicheva AU - Bittig, Thomas AU - Seum, Carole AU - Jülicher, Frank AU - González-Gaitán, Marcos A ID - 1724 IS - 6021 JF - Science TI - Dynamics of Dpp signaling and proliferation control VL - 331 ER - TY - JOUR AB - We report on a technique enabling electrical control of the contact silicidation process in silicon nanowire devices. Undoped silicon nanowires were contacted by pairs of nickel electrodes and each contact was selectively silicided by means of the Joule effect. By a realtime monitoring of the nanowire electrical resistance during the contact silicidation process we were able to fabricate nickel-silicide/silicon/nickel- silicide devices with controlled silicon channel length down to 8 nm. AU - Mongillo, Massimo AU - Spathis, Panayotis AU - Katsaros, Georgios AU - Gentile, Pascal AU - Sanquer, Marc AU - De Franceschi, Silvano ID - 1754 IS - 9 JF - ACS Nano TI - Joule-assisted silicidation for short-channel silicon nanowire devices VL - 5 ER - TY - JOUR AB - Spin-selective tunneling of holes in SiGe nanocrystals contacted by normal-metal leads is reported. The spin selectivity arises from an interplay of the orbital effect of the magnetic field with the strong spin-orbit interaction present in the valence band of the semiconductor. We demonstrate both experimentally and theoretically that spin-selective tunneling in semiconductor nanostructures can be achieved without the use of ferromagnetic contacts. The reported effect, which relies on mixing the light and heavy holes, should be observable in a broad class of quantum-dot systems formed in semiconductors with a degenerate valence band. AU - Georgios Katsaros AU - Golovach, Vitaly N AU - Spathis, Panayotis N AU - Ares, Natalia AU - Stoffel, Mathieu AU - Fournel, Frank AU - Schmidt, Oliver G AU - Glazman, Leonid I AU - De Franceschi, Silvano ID - 1755 IS - 24 JF - Physical Review Letters TI - Observation of spin-selective tunneling in sige nanocrystals VL - 107 ER - TY - CONF AB - Superconducting circuits have been successfully established as systems to prepare and investigate microwave light fields at the quantum level. In contrast to optical experiments where light is detected using photon counters, microwaves are usually measured with well developed linear amplifiers. This makes measurements of correlation functions - one of the important tools in optics - harder to achieve because they traditionally rely on photon counters and beam splitters. Here, we demonstrate a system where we can prepare on demand single microwave photons in a cavity and detect them at the two outputs of the cavity using linear amplifiers. Together with efficient data processing, this allows us to measure different observables of the cavity photons, including the first-order correlation function. Using these techniques we demonstrate cooling of a thermal background field in the cavity. AU - Bozyigit, Deniz AU - Lang, C AU - Steffen, L. Kraig AU - Johannes Fink AU - Eichler, Christopher AU - Baur, Matthias P AU - Bianchetti, R AU - Leek, Peter J AU - Filipp, Stefan AU - Wallraff, Andreas AU - Da Silva, Marcus P AU - Blais, Alexandre ID - 1776 IS - 1 TI - Correlation measurements of individual microwave photons emitted from a symmetric cavity VL - 264 ER - TY - JOUR AB - A wide range of experiments studying microwave photons localized in superconducting cavities have made important contributions to our understanding of the quantum properties of radiation. Propagating microwave photons, however, have so far been studied much less intensely. Here we present measurements in which we reconstruct the quantum state of itinerant single photon Fock states and their superposition with the vacuum by analyzing moments of the measured amplitude distribution up to fourth order. Using linear amplifiers and quadrature amplitude detectors, we have developed efficient methods to separate the detected single photon signal from the noise added by the amplifier. From our measurement data we have also reconstructed the corresponding Wigner function. AU - Eichler, Christopher AU - Bozyigit, Deniz AU - Lang, C AU - Steffen, L. AU - Fink, Johannes M AU - Wallraff, Andreas ID - 1777 IS - 22 JF - Physical Review Letters TI - Experimental state tomography of itinerant single microwave photons VL - 106 ER - TY - JOUR AB - Creating a train of single photons and monitoring its propagation and interaction is challenging in most physical systems, as photons generally interact very weakly with other systems. However, when confining microwave frequency photons in a transmission line resonator, effective photon-photon interactions can be mediated by qubits embedded in the resonator. Here, we observe the phenomenon of photon blockade through second-order correlation function measurements. The experiments clearly demonstrate antibunching in a continuously pumped source of single microwave photons measured by using microwave beam splitters, linear amplifiers, and quadrature amplitude detectors. We also investigate resonance fluorescence and Rayleigh scattering in Mollow-triplet-like spectra. AU - Lang, C AU - Bozyigit, Deniz AU - Eichler, Christopher AU - Steffen, L. Kraig AU - Johannes Fink AU - Abdumalikov, Abdufarrukh A AU - Baur, Matthias P AU - Filipp, Stefan AU - Da Silva, Marcus P AU - Blais, Alexandre AU - Wallraff, Andreas ID - 1778 IS - 24 JF - Physical Review Letters TI - Observation of resonant photon blockade at microwave frequencies using correlation function measurements VL - 106 ER - TY - JOUR AB - At optical frequencies the radiation produced by a source, such as a laser, a black body or a single-photon emitter, is frequently characterized by analysing the temporal correlations of emitted photons using single-photon counters. At microwave frequencies, however, there are no efficient single-photon counters yet. Instead, well-developed linear amplifiers allow for efficient measurement of the amplitude of an electromagnetic field. Here, we demonstrate first- and second-order correlation function measurements of a pulsed microwave-frequency single-photon source integrated on the same chip with a 50/50 beam splitter followed by linear amplifiers and quadrature amplitude detectors. We clearly observe single-photon coherence in first-order and photon antibunching in second-order correlation function measurements of the propagating fields. AU - Bozyigit, Deniz AU - Lang, C AU - Steffen, L. Kraig AU - Johannes Fink AU - Eichler, Christopher AU - Baur, Matthias P AU - Bianchetti, R AU - Leek, Peter J AU - Filipp, Stefan AU - Da Silva, Marcus P AU - Blais, Alexandre AU - Wallraff, Andreas ID - 1775 IS - 2 JF - Nature Physics TI - Antibunching of microwave-frequency photons observed in correlation measurements using linear detectors VL - 7 ER -