TY - JOUR AB - Given a possibly reducible and non-reduced spectral cover π: X → C over a smooth projective complex curve C we determine the group of connected components of the Prym variety Prym(X/C). As an immediate application we show that the finite group of n-torsion points of the Jacobian of C acts trivially on the cohomology of the twisted SL n-Higgs moduli space up to the degree which is predicted by topological mirror symmetry. In particular this yields a new proof of a result of Harder-Narasimhan, showing that this finite group acts trivially on the cohomology of the twisted SL n stable bundle moduli space. AU - Tamas Hausel AU - Pauly, Christian ID - 1471 IS - 3 JF - Geometry and Topology TI - Prym varieties of spectral covers VL - 16 ER - TY - JOUR AB - For given non-zero integers a, b, q we investigate the density of solutions (x, y) ∈ ℤ2 to the binary cubic congruence ax2 + by3 ≡ 0 mod q, and use it to establish the Manin conjecture for a singular del Pezzo surface of degree 2 defined over ℚ. AU - Timothy Browning AU - Baier, Stephan ID - 171 IS - 680 JF - Journal fur die Reine und Angewandte Mathematik TI - Inhomogeneous cubic congruences and rational points on del Pezzo surfaces VL - 2013 ER - TY - JOUR AB - The spatial organization of cell fates during development involves the interpretation of morphogen gradients by cellular signaling cascades and transcriptional networks. Recent studies use biophysical models, genetics, and quantitative imaging to unravel how tissue-level morphogen behavior arises from subcellular events. Moreover, data from several systems show that morphogen gradients, downstream signaling, and the activity of cell-intrinsic transcriptional networks change dynamically during pattern formation. Studies from Drosophila and now also vertebrates suggest that transcriptional network dynamics are central to the generation of gene expression patterns. Together, this leads to the view that pattern formation is an emergent behavior that results from the coordination of events occurring across molecular, cellular, and tissue scales. The development of novel approaches to study this complex process remains a challenge. AU - Anna Kicheva AU - Cohen, Michael H AU - Briscoe, James ID - 1725 IS - 6104 JF - Science TI - Developmental pattern formation: Insights from physics and biology VL - 338 ER - TY - JOUR AB - Self-assembled Ge wires with a height of only 3 unit cells and a length of up to 2 micrometers were grown on Si(001) by means of a catalyst-free method based on molecular beam epitaxy. The wires grow horizontally along either the [100] or the [010] direction. On atomically flat surfaces, they exhibit a highly uniform, triangular cross section. A simple thermodynamic model accounts for the existence of a preferential base width for longitudinal expansion, in quantitative agreement with the experimental findings. Despite the absence of intentional doping, the first transistor-type devices made from single wires show low-resistive electrical contacts and single-hole transport at sub-Kelvin temperatures. In view of their exceptionally small and self-defined cross section, these Ge wires hold promise for the realization of hole systems with exotic properties and provide a new development route for silicon-based nanoelectronics. AU - Zhang, Jianjun AU - Georgios Katsaros AU - Montalenti, Francesco AU - Scopece, Daniele AU - Rezaev, Roman O AU - Mickel, Christine H AU - Rellinghaus, Bernd AU - Miglio, Leo P AU - De Franceschi, Silvano AU - Rastelli, Armando AU - Schmidt, Oliver G ID - 1757 IS - 8 JF - Physical Review Letters TI - Monolithic growth of ultrathin Ge nanowires on Si(001) VL - 109 ER - TY - JOUR AB - We studied the low-energy states of spin-1/2 quantum dots defined in InAs/InP nanowires and coupled to aluminum superconducting leads. By varying the superconducting gap Δ with a magnetic field B we investigated the transition from strong coupling Δ≪T K to weak-coupling Δ≫T K, where T K is the Kondo temperature. Below the critical field, we observe a persisting zero-bias Kondo resonance that vanishes only for low B or higher temperatures, leaving the room to more robust subgap structures at bias voltages between Δ and 2Δ. For strong and approximately symmetric tunnel couplings, a Josephson supercurrent is observed in addition to the Kondo peak. We ascribe the coexistence of a Kondo resonance and a superconducting gap to a significant density of intragap quasiparticle states, and the finite-bias subgap structures to tunneling through Shiba states. Our results, supported by numerical calculations, own relevance also in relation to tunnel-spectroscopy experiments aiming at the observation of Majorana fermions in hybrid nanostructures. AU - Lee, Eduardo J AU - Jiang, Xiaocheng AU - Aguado, Ramón AU - Georgios Katsaros AU - Lieber, Charles M AU - De Franceschi, Silvano ID - 1758 IS - 18 JF - Physical Review Letters TI - Zero-bias anomaly in a nanowire quantum dot coupled to superconductors VL - 109 ER - TY - JOUR AB - We report on the electronic transport properties of multiple-gate devices fabricated from undoped silicon nanowires. Understanding and control of the relevant transport mechanisms was achieved by means of local electrostatic gating and temperature-dependent measurements. The roles of the source/drain contacts and of the silicon channel could be independently evaluated and tuned. Wrap gates surrounding the silicide-silicon contact interfaces were proved to be effective in inducing a full suppression of the contact Schottky barriers, thereby enabling carrier injection down to liquid helium temperature. By independently tuning the effective Schottky barrier heights, a variety of reconfigurable device functionalities could be obtained. In particular, the same nanowire device could be configured to work as a Schottky barrier transistor, a Schottky diode, or a p-n diode with tunable polarities. This versatility was eventually exploited to realize a NAND logic gate with gain well above one. AU - Mongillo, Massimo AU - Spathis, Panayotis N AU - Georgios Katsaros AU - Gentile, Pascal AU - De Franceschi, Silvano ID - 1756 IS - 6 JF - Nano Letters TI - Multifunctional devices and logic gates with undoped silicon nanowires VL - 12 ER - TY - JOUR AB - Nonlinearity and entanglement are two important properties by which physical systems can be identified as nonclassical. We study the dynamics of the resonant interaction of up to N=3 two-level systems and a single mode of the electromagnetic field sharing a single excitation dynamically. We observe coherent vacuum Rabi oscillations and their nonlinear √N speedup by tracking the populations of all qubits and the resonator in time. We use quantum state tomography to show explicitly that the dynamics generates maximally entangled states of the W class in a time limited only by the collective interaction rate. We use an entanglement witness and the 3-tangle to characterize the state whose fidelity F=78% is limited in our experiments by crosstalk arising during the simultaneous qubit manipulations which is absent in a sequential approach with F=91%. AU - Mlynek, Jonas A AU - Abdumalikov, Abdufarrukh A AU - Johannes Fink AU - Steffen, L. Kraig AU - Baur, Matthias P AU - Lang, C AU - Van Loo, Arjan F AU - Wallraff, Andreas ID - 1783 IS - 5 JF - Physical Review A - Atomic, Molecular, and Optical Physics TI - Demonstrating W-type entanglement of Dicke states in resonant cavity quantum electrodynamics VL - 86 ER - TY - JOUR AB - Steering a quantum harmonic oscillator state along cyclic trajectories leads to a path-dependent geometric phase. Here we describe its experimental observation in an electronic harmonic oscillator. We use a superconducting qubit as a nonlinear probe of the phase, which is otherwise unobservable due to the linearity of the oscillator. We show that the geometric phase is, for a variety of cyclic paths, proportional to the area enclosed in the quadrature plane. At the transition to the nonadiabatic regime, we study corrections to the phase and dephasing of the qubit caused by qubit-resonator entanglement. In particular, we identify parameters for which this dephasing mechanism is negligible even in the nonadiabatic regime. The demonstrated controllability makes our system a versatile tool to study geometric phases in open quantum systems and to investigate their potential for quantum information processing. AU - Pechal, M AU - Berger, Stefan T AU - Abdumalikov, Abdufarrukh A AU - Johannes Fink AU - Mlynek, Jonas A AU - Steffen, L. Kraig AU - Wallraff, Andreas AU - Filipp, Stefan ID - 1782 IS - 17 JF - Physical Review Letters TI - Geometric phase and nonadiabatic effects in an electronic harmonic oscillator VL - 108 ER - TY - JOUR AB - A localized qubit entangled with a propagating quantum field is well suited to study nonlocal aspects of quantum mechanics and may also provide a channel to communicate between spatially separated nodes in a quantum network. Here, we report the on-demand generation and characterization of Bell-type entangled states between a superconducting qubit and propagating microwave fields composed of zero-, one-, and two-photon Fock states. Using low noise linear amplification and efficient data acquisition we extract all relevant correlations between the qubit and the photon states and demonstrate entanglement with high fidelity. AU - Eichler, Christopher AU - Lang, C AU - Johannes Fink AU - Govenius, J AU - Filipp, Stefan AU - Wallraff, Andreas ID - 1784 IS - 24 JF - Physical Review Letters TI - Observation of entanglement between itinerant microwave photons and a superconducting qubit VL - 109 ER - TY - JOUR AB - Brain circuits are assembled from a large variety of morphologically and functionally diverse cell types. It is not known how the intermingled cell types of an individual adult brain region differ in their expressed genomes. Here we describe an atlas of cell type transcriptomes in one brain region, the mouse retina. We found that each adult cell type expressed a specific set of genes, including a unique set of transcription factors, forming a 'barcode' for cell identity. Cell type transcriptomes carried enough information to categorize cells into morphological classes and types. Several genes that were specifically expressed in particular retinal circuit elements, such as inhibitory neuron types, are associated with eye diseases. The resource described here allows gene expression to be compared across adult retinal cell types, experimenting with specific transcription factors to differentiate stem or somatic cells to retinal cell types, and predicting cellular targets of newly discovered disease-associated genes. AU - Sandra Siegert AU - Cabuy, Erik AU - Scherf, Brigitte G AU - Kohler, Hubertus AU - Panda, Satchidananda AU - Le, Yunzheng AU - Fehling, Hans J AU - Gaidatzis, Dimos AU - Stadler, Michael B AU - Roska, Botond M ID - 1801 IS - 3 JF - Nature Neuroscience TI - Transcriptional code and disease map for adult retinal cell types VL - 15 ER -