@article{1470, abstract = {We show that a natural isomorphism between the rational cohomology groups of the two zero-dimensional Hilbert schemes of n-points of two surfaces, the affine plane minus the axes and the cotangent bundle of an elliptic curve, exchanges the weight filtration on the first set of cohomology groups with the perverse Leray filtration associated with a natural fibration on the second set of cohomology groups. We discuss some associated hard Lefschetz phenomena.}, author = {De Cataldo, Mark A and Tamas Hausel and Migliorini, Luca}, journal = {Journal of Singularities}, pages = {23 -- 38}, publisher = {Worldwide Center of Mathematics}, title = {{Exchange between perverse and weight filtration for the Hilbert schemes of points of two surfaces}}, doi = {10.5427/jsing.2013.7c}, volume = {7}, year = {2013}, } @article{1785, abstract = {The geometric aspects of quantum mechanics are emphasized most prominently by the concept of geometric phases, which are acquired whenever a quantum system evolves along a path in Hilbert space, that is, the space of quantum states of the system. The geometric phase is determined only by the shape of this path and is, in its simplest form, a real number. However, if the system has degenerate energy levels, then matrix-valued geometric state transformations, known as non-Abelian holonomies-the effect of which depends on the order of two consecutive paths-can be obtained. They are important, for example, for the creation of synthetic gauge fields in cold atomic gases or the description of non-Abelian anyon statistics. Moreover, there are proposals to exploit non-Abelian holonomic gates for the purposes of noise-resilient quantum computation. In contrast to Abelian geometric operations, non-Abelian ones have been observed only in nuclear quadrupole resonance experiments with a large number of spins, and without full characterization of the geometric process and its non-commutative nature. Here we realize non-Abelian non-adiabatic holonomic quantum operations on a single, superconducting, artificial three-level atom by applying a well-controlled, two-tone microwave drive. Using quantum process tomography, we determine fidelities of the resulting non-commuting gates that exceed 95 per cent. We show that two different quantum gates, originating from two distinct paths in Hilbert space, yield non-equivalent transformations when applied in different orders. This provides evidence for the non-Abelian character of the implemented holonomic quantum operations. In combination with a non-trivial two-quantum-bit gate, our method suggests a way to universal holonomic quantum computing.}, author = {Abdumalikov, Abdufarrukh A and Johannes Fink and Juliusson, K and Pechal, M and Berger, Stefan T and Wallraff, Andreas and Filipp, Stefan}, journal = {Nature}, number = {7446}, pages = {482 -- 485}, publisher = {Nature Publishing Group}, title = {{Experimental realization of non-Abelian non-adiabatic geometric gates}}, doi = {10.1038/nature12010}, volume = {496}, year = {2013}, } @article{1786, abstract = {We report the experimental observation and a theoretical explanation of collective suppression of linewidths for multiple superconducting qubits coupled to a good cavity. This demonstrates how strong qubit-cavity coupling can significantly modify the dephasing and dissipation processes that might be expected for individual qubits, and can potentially improve coherence times in many-body circuit QED.}, author = {Nissen, Felix and Johannes Fink and Mlynek, Jonas A and Wallraff, Andreas and Keeling, Jonathan M}, journal = {Physical Review Letters}, number = {20}, publisher = {American Physical Society}, title = {{Collective suppression of linewidths in circuit QED}}, doi = {10.1103/PhysRevLett.110.203602}, volume = {110}, year = {2013}, } @article{1787, abstract = {When two indistinguishable single photons impinge at the two inputs of a beam splitter they coalesce into a pair of photons appearing in either one of its two outputs. This effect is due to the bosonic nature of photons and was first experimentally observed by Hong, Ou and Mandel. Here, we present the observation of the Hong-Ou-Mandel effect with two independent single-photon sources in the microwave frequency domain. We probe the indistinguishability of single photons, created with a controllable delay, in time-resolved second-order cross- and auto-correlation function measurements. Using quadrature amplitude detection we are able to resolve different photon numbers and detect coherence in and between the output arms. This scheme allows us to fully characterize the two-mode entanglement of the spatially separated beam-splitter output modes. Our experiments constitute a first step towards using two-photon interference at microwave frequencies for quantum communication and information processing.}, author = {Lang, C and Eichler, Christopher and Steffen, L. Kraig and Johannes Fink and Woolley, Matthew J and Blais, Alexandre and Wallraff, Andreas}, journal = {Nature Physics}, number = {6}, pages = {345 -- 348}, publisher = {Nature Publishing Group}, title = {{Correlations, indistinguishability and entanglement in Hong-Ou-Mandel experiments at microwave frequencies}}, doi = {10.1038/nphys2612}, volume = {9}, year = {2013}, } @article{1790, abstract = {In the September 12, 2013 issue of Nature, the Epi4K Consortium (. Allen etal., 2013) reported sequencing 264patient trios with epileptic encephalopathies. The Consortium focused on genes exceptionally intolerant to sequence variations and found substantial interconnections with autism and intellectual disability gene networks.}, author = {Gaia Novarino and Baek, SeungTae and Gleeson, Joseph G}, journal = {Neuron}, number = {1}, pages = {9 -- 11}, publisher = {Elsevier}, title = {{The sacred disease: The puzzling genetics of epileptic disorders}}, doi = {10.1016/j.neuron.2013.09.019}, volume = {80}, year = {2013}, } @article{17991, abstract = {Electrical and thermal transport properties of C60 molecules are investigated with density-functional-theory based calculations. These calculations suggest that the optimum contact geometry for an electrode terminated with a single-Au atom is through binding to one or two C-atoms of C60 with a tendency to promote the  sp2-hybridization into an  sp3-type one. Transport in these junctions is primarily through an unoccupied molecular orbital that is partly hybridized with the Au, which results in splitting the degeneracy of the lowest unoccupied molecular orbital triplet. The transmission through these junctions, however, cannot be modeled by a single Lorentzian resonance, as our results show evidence of quantum interference between an occupied and an unoccupied orbital. The interference results in a suppression of conductance around the Fermi energy. Our numerical findings are readily analyzed analytically within a simple two-level model.}, author = {Géranton, G. and Seiler, C. and Bagrets, A. and Venkataraman, Latha and Evers, F.}, issn = {1089-7690}, journal = {The Journal of Chemical Physics}, number = {23}, publisher = {AIP Publishing}, title = {{Transport properties of individual C60-molecules}}, doi = {10.1063/1.4840535}, volume = {139}, year = {2013}, } @article{17992, abstract = {Here we demonstrate for the first time that strained silanes couple directly to gold electrodes in break-junction conductance measurements. We find that strained silicon molecular wires terminated by alkyl sulfide aurophiles behave effectively as single-molecule parallel circuits with competing sulfur-to-sulfur (low G) and sulfur-to-silacycle (high G) pathways. We can switch off the high conducting sulfur-to-silacycle pathway by altering the environment of the electrode surface to disable the Au–silacycle coupling. Additionally, we can switch between conductive pathways in a single molecular junction by modulating the tip–substrate electrode distance. This study provides a new molecular design to control electronics in silicon-based single molecule wires.}, author = {Su, Timothy A. and Widawsky, Jonathan R. and Li, Haixing and Klausen, Rebekka S. and Leighton, James L. and Steigerwald, Michael L. and Venkataraman, Latha and Nuckolls, Colin}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, number = {49}, pages = {18331--18334}, publisher = {American Chemical Society}, title = {{Silicon ring strain creates high-conductance pathways in single-molecule circuits}}, doi = {10.1021/ja410656a}, volume = {135}, year = {2013}, } @article{17993, abstract = {We demonstrate a new method of achieving rectification in single molecule devices using the high-bias properties of gold–carbon bonds. Our design for molecular rectifiers uses a symmetric, conjugated molecular backbone with a single methylsulfide group linking one end to a gold electrode and a covalent gold–carbon bond at the other end. The gold–carbon bond results in a hybrid gold-molecule “gateway” state pinned close to the Fermi level of one electrode. Through nonequilibrium transport calculations, we show that the energy of this state shifts drastically with applied bias, resulting in rectification at surprisingly low voltages. We use this concept to design and synthesize a family of diodes and demonstrate through single-molecule current–voltage measurements that the rectification ratio can be predictably and efficiently tuned. This result constitutes the first experimental demonstration of a rationally tunable system of single-molecule rectifiers. More generally, the results demonstrate that the high-bias properties of “gateway” states can be used to provide additional functionality to molecular electronic systems.}, author = {Batra, Arunabh and Darancet, Pierre and Chen, Qishui and Meisner, Jeffrey S. and Widawsky, Jonathan R. and Neaton, Jeffrey B. and Nuckolls, Colin and Venkataraman, Latha}, issn = {1530-6992}, journal = {Nano Letters}, number = {12}, pages = {6233--6237}, publisher = {American Chemical Society}, title = {{Tuning rectification in single-molecular diodes}}, doi = {10.1021/nl403698m}, volume = {13}, year = {2013}, } @article{17994, abstract = {Charge transfer through noncovalent interactions is crucial to a variety of chemical phenomena. These interactions are often weak and nonspecific and can coexist, making it difficult to isolate the transfer efficiency of one type of bond versus another. Here, we show how core-hole clock spectroscopy can be used to measure charge transfer through noncovalent interactions. We study the model system 1,4-benzenediamine molecules bound on an Au surface through an Au–N donor–acceptor bond as these are known to provide a pathway for electronic conduction in molecular devices. We study different phases of the molecule/Au system and map charge delocalization times from carbon and nitrogen sites on the molecule. We show that charge delocalization across Au–N donor–acceptor bond occurs in less than 500 as. Furthermore, the Au–N bond also enhances delocalization times from neighboring carbon sites, demonstrating that fast charge transfer across a metal–organic interface does not require a covalently bonded system.}, author = {Kladnik, Gregor and Cvetko, Dean and Batra, Arunabh and Dell’Angela, Martina and Cossaro, Albano and Kamenetska, Maria and Venkataraman, Latha and Morgante, Alberto}, issn = {1932-7455}, journal = {The Journal of Physical Chemistry C}, number = {32}, pages = {16477--16482}, publisher = {American Chemical Society}, title = {{Ultrafast charge transfer through noncovalent Au–N interactions in molecular systems}}, doi = {10.1021/jp405229b}, volume = {117}, year = {2013}, } @article{17995, abstract = {We have measured the single-molecule conductance of a family of bithiophene derivatives terminated with methyl sulfide gold-binding linkers using a scanning tunneling microscope based break-junction technique. We find a broad distribution in the single-molecule conductance of bithiophene compared with that of a methyl sulfide terminated biphenyl. Using a combination of experiments and calculations, we show that this increased breadth in the conductance distribution is explained by the difference in 5-fold symmetry of thiophene rings as compared to the 6-fold symmetry of benzene rings. The reduced symmetry of thiophene rings results in a restriction on the torsion angle space available to these molecules when bound between two metal electrodes in a junction, causing each molecular junction to sample a different set of conformers in the conductance measurements. In contrast, the rotations of biphenyl are essentially unimpeded by junction binding, allowing each molecular junction to sample similar conformers. This work demonstrates that the conductance of bithiophene displays a strong dependence on the conformational fluctuations accessible within a given junction configuration, and that the symmetry of such small molecules can significantly influence their conductance behaviors.}, author = {Dell, Emma J. and Capozzi, Brian and DuBay, Kateri H. and Berkelbach, Timothy C. and Moreno, Jose Ricardo and Reichman, David R. and Venkataraman, Latha and Campos, Luis M.}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, number = {32}, pages = {11724--11727}, publisher = {American Chemical Society}, title = {{Impact of molecular symmetry on single-molecule conductance}}, doi = {10.1021/ja4055367}, volume = {135}, year = {2013}, } @article{17996, abstract = {We compare the conductance of a series of amine-terminated oligophenyl and alkane molecular junctions formed with Ag and Au electrodes using the scanning tunneling microscope based break-junction technique. For these molecules that conduct through the highest occupied molecular orbital, junctions formed with Au electrodes are more conductive than those formed with Ag electrodes, consistent with the lower work function for Ag. The measured conductance decays exponentially with molecular backbone length with a decay constant that is essentially the same for Ag and Au electrodes. However, the formation and evolution of molecular junctions upon elongation are very different for these two metals. Specifically, junctions formed with Ag electrodes sustain significantly longer elongation when compared with Au due to a difference in the initial gap opened up when the metal point-contact is broken. Using this observation and density functional theory calculations of junction structure and conductance we explain the trends observed in the single molecule junction conductance. Our work thus opens a new path to the conductance measurements of a single molecule junction in Ag electrodes.}, author = {Kim, Taekyeong and Vázquez, Héctor and Hybertsen, Mark S. and Venkataraman, Latha}, issn = {1530-6992}, journal = {Nano Letters}, number = {7}, pages = {3358--3364}, publisher = {American Chemical Society}, title = {{Conductance of molecular junctions formed with silver electrodes}}, doi = {10.1021/nl401654s}, volume = {13}, year = {2013}, } @article{17997, abstract = {We report the simultaneous measurement of conductance and thermopower of highly conducting single-molecule junctions using a scanning tunneling microscope-based break-junction setup. We start with molecular backbones (alkanes and oligophenyls) terminated with trimethyltin end groups that cleave off in situ to create junctions where terminal carbons are covalently bonded to the Au electrodes. We apply a thermal gradient across these junctions and measure their conductance and thermopower. Because of the electronic properties of the highly conducting Au–C links, the thermoelectric properties and power factor are very high. Our results show that the molecular thermopower increases nonlinearly with the molecular length while conductance decreases exponentially with increasing molecular length. Density functional theory calculations show that a gateway state representing the Au–C covalent bond plays a key role in the conductance. With this as input, we analyze a series of simplified models and show that a tight-binding model that explicitly includes the gateway states and the molecular backbone states accurately captures the experimentally measured conductance and thermopower trends.}, author = {Widawsky, J. R. and Chen, W. and Vázquez, H. and Kim, T. and Breslow, R. and Hybertsen, M. S. and Venkataraman, Latha}, issn = {1530-6992}, journal = {Nano Letters}, number = {6}, pages = {2889--2894}, publisher = {American Chemical Society}, title = {{Length-dependent thermopower of highly conducting Au–C bonded single molecule junctions}}, doi = {10.1021/nl4012276}, volume = {13}, year = {2013}, } @article{17998, abstract = {We measure simultaneously force and conductance of Ag metal point-contacts under ambient conditions at room temperature. We observe the formation of contacts with a conductance close to 1 G0, the quantum of conductance, which can be attributed to a single-atom contact, similar to those formed by Au. We also find two additional conductance features at ∼0.4 G0 and ∼1.3 G0, which have been previously ascribed to contacts with oxygen contaminations. Here, using a conductance cross-correlation technique, we distinguish three different atomic-scale structural motifs and analyze their rupture forces and stiffness. Our results allow us to assign the ∼0.4 G0 conductance feature to an Ag–O–Ag contact and the ∼1.3 G0 feature to an Ag–Ag single-atom contact with an oxygen atom in parallel. Utilizing complementary information from force and conductance, we thus demonstrate the correlation of conductance with the structural evolution at the atomic scale.}, author = {Aradhya, Sriharsha V. and Frei, Michael and Halbritter, András and Venkataraman, Latha}, issn = {1936-086X}, journal = {ACS Nano}, number = {4}, pages = {3706--3712}, publisher = {American Chemical Society}, title = {{Correlating structure, conductance, and mechanics of silver atomic-scale contacts}}, doi = {10.1021/nn4007187}, volume = {7}, year = {2013}, } @article{17999, abstract = {The idea of using individual molecules as active electronic components provided the impetus to develop a variety of experimental platforms to probe their electronic transport properties. Among these, single-molecule junctions in a metal–molecule–metal motif have contributed significantly to our fundamental understanding of the principles required to realize molecular-scale electronic components from resistive wires to reversible switches. The success of these techniques and the growing interest of other disciplines in single-molecule-level characterization are prompting new approaches to investigate metal–molecule–metal junctions with multiple probes. Going beyond electronic transport characterization, these new studies are highlighting both the fundamental and applied aspects of mechanical, optical and thermoelectric properties at the atomic and molecular scales. Furthermore, experimental demonstrations of quantum interference and manipulation of electronic and nuclear spins in single-molecule circuits are heralding new device concepts with no classical analogues. In this Review, we present the emerging methods being used to interrogate multiple properties in single molecule-based devices, detail how these measurements have advanced our understanding of the structure–function relationships in molecular junctions, and discuss the potential for future research and applications.}, author = {Aradhya, Sriharsha V. and Venkataraman, Latha}, issn = {1748-3395}, journal = {Nature Nanotechnology}, number = {6}, pages = {399--410}, publisher = {Springer Nature}, title = {{Single-molecule junctions beyond electronic transport}}, doi = {10.1038/nnano.2013.91}, volume = {8}, year = {2013}, } @inbook{18351, abstract = {Motion-based segmentation is an important tool for the analysis of articulated shapes. As such, it plays an important role in mechanical engineering, computer graphics, and computer vision. In this chapter, we study motion-based segmentation of 3D articulated shapes. We formulate motion-based surface segmentation as a piecewise-smooth regularization problem for the transformations between several poses. Using Lie-group representation for the transformation at each surface point, we obtain a simple regularized fitting problem. An Ambrosio-Tortorelli scheme of a generalized Mumford-Shah model gives us the segmentation functional without assuming prior knowledge on the number of parts or even the articulated nature of the object. Experiments on several standard datasets compare the results of the proposed method to state-of-the-art algorithms.}, author = {Rosman, Guy and Bronstein, Michael M. and Bronstein, Alexander and Wolf, Alon and Kimmel, Ron}, booktitle = {Innovations for Shape Analysis}, editor = {Breuß, Michael and Bruckstein, Alfred and Maragos, Petros}, isbn = {9783642341403}, issn = {1612-3786}, pages = {263--281}, publisher = {Springer Nature}, title = {{Group-Valued Regularization for Motion Segmentation of Articulated Shapes}}, doi = {10.1007/978-3-642-34141-0_12}, year = {2013}, } @inbook{18352, abstract = {Feature-based analysis is becoming a very popular approach for geometric shape analysis. Following the success of this approach in image analysis, there is a growing interest in finding analogous methods in the 3D world. Maximally stable component detection is a low computation cost and high repeatability method for feature detection in images.In this study, a diffusion-geometry based framework for stable component detection is presented, which can be used for geometric feature detection in deformable shapes.The vast majority of studies of deformable 3D shapes models them as the two-dimensional boundary of the volume of the shape. Recent works have shown that a volumetric shape model is advantageous in numerous ways as it better captures the natural behavior of non-rigid deformations. We show that our framework easily adapts to this volumetric approach, and even demonstrates superior performance.A quantitative evaluation of our methods on the SHREC’10 and SHREC’11 feature detection benchmarks as well as qualitative tests on the SCAPE dataset show its potential as a source of high-quality features. Examples demonstrating the drawbacks of surface stable components and the advantage of their volumetric counterparts are also presented.}, author = {Litman, Roee and Bronstein, Alexander and Bronstein, Michael M.}, booktitle = {Innovations for Shape Analysis}, editor = {Breuß, Michael and Bruckstein, Alfred and Maragos, Petros}, isbn = {9783642341403}, issn = {1612-3786}, pages = {161 -- 189}, publisher = {Springer Nature}, title = {{Stable Semi-local Features for Non-rigid Shapes}}, doi = {10.1007/978-3-642-34141-0_8}, year = {2013}, } @inproceedings{18385, abstract = {In this paper we present a framework for real time enhancement of speech signals. Our method leverages a new process-centric approach for sparse and parsimonious models, where the representation pursuit is obtained applying a deterministic function or process rather than solving an optimization problem. We first propose a rank-regularized robust version of non-negative matrix factorization (NMF) for modeling time-frequency representations of speech signals in which the spectral frames are decomposed as sparse linear combinations of atoms of a low-rank dictionary. Then, a parametric family of pursuit processes is derived from the iteration of the proximal descent method for solving this model. We present several experiments showing successful results and the potential of the proposed framework. Incorporating discriminative learning makes the proposed method significantly outperform exact NMF algorithms, with fixed latency and at a fraction of it's computational complexity.}, author = {Sprechmann, Pablo and Bronstein, Alexander and Bronstein, Michael and Sapiro, Guillermo}, booktitle = {2013 IEEE International Conference on Acoustics, Speech and Signal Processing}, issn = {2379-190X}, location = {Vancouver, BC, Canada}, publisher = {IEEE}, title = {{Learnable low rank sparse models for speech denoising}}, doi = {10.1109/icassp.2013.6637624}, year = {2013}, } @inproceedings{18386, abstract = {A method for removing impulse noise from audio signals by fusing multiple copies of the same recording is introduced in this paper. The proposed algorithm exploits the fact that while in general multiple copies of a given recording are available, all sharing the same master, most degradations in audio signals are record-dependent. Our method first seeks for the optimal non-rigid alignment of the signals that is robust to the presence of sparse outliers with arbitrary magnitude. Unlike previous approaches, we simultaneously find the optimal alignment of the signals and impulsive degradation. This is obtained via continuous dynamic time warping computed solving an Eikonal equation. We propose to use our approach in the derivative domain, reconstructing the signal by solving an inverse problem that resembles the Poisson image editing technique. The proposed framework is here illustrated and tested in the restoration of old gramophone recordings showing promising results; however, it can be used in other applications where different copies of the signal of interest are available and the degradations are copy-dependent.}, author = {Sprechmann, Pablo and Bronstein, Alexander and Morel, Jean-Michel and Sapiro, Guillermo}, booktitle = {2013 IEEE International Conference on Acoustics, Speech and Signal Processing}, issn = {2379-190X}, location = {Vancouver, BC, Canada}, publisher = {IEEE}, title = {{Audio restoration from multiple copies}}, doi = {10.1109/icassp.2013.6637774}, year = {2013}, } @inproceedings{18395, abstract = {Dynamic Time Warping (DTW), is a simple but efficient technique for matching sequences with rigid deformation. Therefore, it is frequently used for matching shapes in general, and shapes of handwritten words in Document Image Analysis tasks. As DTW is computationally expensive, efficient algorithms for fast computation are crucial. Retrieving images from large scale datasets using DTW, suffers from the constraint of linear searching of all sample in the datasets. Fast approximation algorithms for image retrieval are mostly based on normed spaces where the triangle inequality holds, which is unfortunately not the case with the DTW metric. In this paper we present a novel approach for fast search of handwritten words within large datasets of shapes. The presented approach is based on the Boost-Map [1] algorithm, for embedding the feature space with the DTW measurement to an euclidean space and use the Local Sensitivity Hashing algorithm (LSH) to rank the k-nearest neighbors of a query image. The algorithm, first, processes and embeds objects of the large data sets to a normed space. Fast approximation of k-nearest neighbors using LSH on the embedding space, generates the top kranked samples which are examined using the real DTW distance to give final accurate results. We demonstrate our method on a database of 45; 800 images of word-parts extracted from the IFN/ENIT database [11] and images collected from 51 different writers. Our method achieves a speedup of 4 orders of magnitude over the exact method, at the cost of only a 2:2% reduction in accuracy.}, author = {Saabni, Raid and Bronstein, Alexander}, booktitle = {2012 International Conference on Frontiers in Handwriting Recognition}, isbn = {9781467322621}, location = {Bari, Italy}, publisher = {IEEE}, title = {{Fast key-word searching using 'BoostMap' based embedding}}, doi = {10.1109/icfhr.2012.204}, year = {2013}, } @article{18421, abstract = {The use of Laplacian eigenbases has been shown to be fruitful in many computer graphics applications. Today, state-of-the-art approaches to shape analysis, synthesis, and correspondence rely on these natural harmonic bases that allow using classical tools from harmonic analysis on manifolds. However, many applications involving multiple shapes are obstacled by the fact that Laplacian eigenbases computed independently on different shapes are often incompatible with each other. In this paper, we propose the construction of common approximate eigenbases for multiple shapes using approximate joint diagonalization algorithms, taking as input a set of corresponding functions (e.g. indicator functions of stable regions) on the two shapes. We illustrate the benefits of the proposed approach on tasks from shape editing, pose transfer, correspondence, and similarity.}, author = {Kovnatsky, A. and Bronstein, M. M. and Bronstein, Alexander and Glashoff, K. and Kimmel, R.}, issn = {1467-8659}, journal = {Computer Graphics Forum}, number = {2pt4}, pages = {439--448}, publisher = {Wiley}, title = {{Coupled quasi‐harmonic bases}}, doi = {10.1111/cgf.12064}, volume = {32}, year = {2013}, }