@inproceedings{1376, abstract = {We consider the distributed synthesis problem for temporal logic specifications. Traditionally, the problem has been studied for LTL, and the previous results show that the problem is decidable iff there is no information fork in the architecture. We consider the problem for fragments of LTL and our main results are as follows: (1) We show that the problem is undecidable for architectures with information forks even for the fragment of LTL with temporal operators restricted to next and eventually. (2) For specifications restricted to globally along with non-nested next operators, we establish decidability (in EXPSPACE) for star architectures where the processes receive disjoint inputs, whereas we establish undecidability for architectures containing an information fork-meet structure. (3) Finally, we consider LTL without the next operator, and establish decidability (NEXPTIME-complete) for all architectures for a fragment that consists of a set of safety assumptions, and a set of guarantees where each guarantee is a safety, reachability, or liveness condition.}, author = {Chatterjee, Krishnendu and Henzinger, Thomas A and Otop, Jan and Pavlogiannis, Andreas}, booktitle = {13th International Conference on Formal Methods in Computer-Aided Design}, location = {Portland, OR, United States}, pages = {18 -- 25}, publisher = {IEEE}, title = {{Distributed synthesis for LTL fragments}}, doi = {10.1109/FMCAD.2013.6679386}, year = {2013}, } @inproceedings{1385, abstract = {It is often difficult to correctly implement a Boolean controller for a complex system, especially when concurrency is involved. Yet, it may be easy to formally specify a controller. For instance, for a pipelined processor it suffices to state that the visible behavior of the pipelined system should be identical to a non-pipelined reference system (Burch-Dill paradigm). We present a novel procedure to efficiently synthesize multiple Boolean control signals from a specification given as a quantified first-order formula (with a specific quantifier structure). Our approach uses uninterpreted functions to abstract details of the design. We construct an unsatisfiable SMT formula from the given specification. Then, from just one proof of unsatisfiability, we use a variant of Craig interpolation to compute multiple coordinated interpolants that implement the Boolean control signals. Our method avoids iterative learning and back-substitution of the control functions. We applied our approach to synthesize a controller for a simple two-stage pipelined processor, and present first experimental results.}, author = {Hofferek, Georg and Gupta, Ashutosh and Könighofer, Bettina and Jiang, Jie and Bloem, Roderick}, booktitle = {2013 Formal Methods in Computer-Aided Design}, location = {Portland, OR, United States}, pages = {77 -- 84}, publisher = {IEEE}, title = {{Synthesizing multiple boolean functions using interpolation on a single proof}}, doi = {10.1109/FMCAD.2013.6679394}, year = {2013}, } @inproceedings{1387, abstract = {Choices made by nondeterministic word automata depend on both the past (the prefix of the word read so far) and the future (the suffix yet to be read). In several applications, most notably synthesis, the future is diverse or unknown, leading to algorithms that are based on deterministic automata. Hoping to retain some of the advantages of nondeterministic automata, researchers have studied restricted classes of nondeterministic automata. Three such classes are nondeterministic automata that are good for trees (GFT; i.e., ones that can be expanded to tree automata accepting the derived tree languages, thus whose choices should satisfy diverse futures), good for games (GFG; i.e., ones whose choices depend only on the past), and determinizable by pruning (DBP; i.e., ones that embody equivalent deterministic automata). The theoretical properties and relative merits of the different classes are still open, having vagueness on whether they really differ from deterministic automata. In particular, while DBP ⊆ GFG ⊆ GFT, it is not known whether every GFT automaton is GFG and whether every GFG automaton is DBP. Also open is the possible succinctness of GFG and GFT automata compared to deterministic automata. We study these problems for ω-regular automata with all common acceptance conditions. We show that GFT=GFG⊃DBP, and describe a determinization construction for GFG automata.}, author = {Boker, Udi and Kuperberg, Denis and Kupferman, Orna and Skrzypczak, Michał}, location = {Riga, Latvia}, number = {PART 2}, pages = {89 -- 100}, publisher = {Springer}, title = {{Nondeterminism in the presence of a diverse or unknown future}}, doi = {10.1007/978-3-642-39212-2_11}, volume = {7966}, year = {2013}, } @article{1442, abstract = {We give a cohomological interpretation of both the Kac polynomial and the refined Donaldson-Thomas-invariants of quivers. This interpretation yields a proof of a conjecture of Kac from 1982 and gives a new perspective on recent work of Kontsevich-Soibelman. Thisis achieved by computing, via an arithmetic Fourier transform, the dimensions of the isotypical components of the cohomology of associated Nakajima quiver varieties under the action of a Weyl group. The generating function of the corresponding Poincare polynomials is an extension of Hua's formula for Kac polynomials of quivers involving Hall-Littlewood symmetric functions. The resulting formulae contain a wide range of information on the geometry of the quiver varieties.}, author = {Tamas Hausel and Letellier, Emmanuel and Rodríguez Villegas, Fernando}, journal = {Annals of Mathematics}, number = {3}, pages = {1147 -- 1168}, publisher = {Princeton University Press}, title = {{Positivity for Kac polynomials and DT-invariants of quivers}}, doi = {10.4007/annals.2013.177.3.8}, volume = {177}, year = {2013}, } @inbook{1443, abstract = {Here we survey several results and conjectures on the cohomology of the total space of the Hitchin system: the moduli space of semi-stable rank n and degree d Higgs bundles on a complex algebraic curve C. The picture emerging is a dynamic mixture of ideas originating in theoretical physics such as gauge theory and mirror symmetry, Weil conjectures in arithmetic algebraic geometry, representation theory of finite groups of Lie type and Langlands duality in number theory.}, author = {Tamas Hausel}, booktitle = {Handbook of Moduli: Volume II}, pages = {29 -- 70}, publisher = {International Press}, title = {{Global topology of the Hitchin system}}, volume = {25}, year = {2013}, } @article{1469, abstract = {We study connections between the topology of generic character varieties of fundamental groups of punctured Riemann surfaces, Macdonald polynomials, quiver representations, Hilbert schemes on Cx × Cx, modular forms and multiplicities in tensor products of irreducible characters of finite general linear groups.}, author = {Tamas Hausel and Letellier, Emmanuel and Rodríguez Villegas, Fernando}, journal = {Advances in Mathematics}, pages = {85 -- 128}, publisher = {Academic Press}, title = {{Arithmetic harmonic analysis on character and quiver varieties II}}, doi = {10.1016/j.aim.2012.10.009}, volume = {234}, year = {2013}, } @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}, }