Computational equivalence of the two inequivalent spinor representations of the braid group in the Ising topological quantum computer

We demonstrate that the two inequivalent spinor representations of the braid group \B_{2n+2}, describing the exchanges of 2n+2 non-Abelian Ising anyons in the Pfaffian topological quantum computer, are equivalent from computational point of view, i.e., the sets of topologically protected quantum gates that could be implemented in both cases by braiding exactly coincide. We give the explicit matrices generating almost all braidings in the spinor representations of the 2n+2 Ising anyons, as well as important recurrence relations. Our detailed analysis allows us to understand better the physical difference between the two inequivalent representations and to propose a process that could determine the type of representation for any concrete physical realization of the Pfaffian quantum computer.Comment: 9 pages, 2 figures, published versio

A Molecular Platinum Cluster Junction: A Single-Molecule Switch

We present a theoretical study of the electronic transport through single-molecule junctions incorporating a Pt6 metal cluster bound within an organic framework. We show that the insertion of this molecule between a pair of electrodes leads to a fully atomically engineered nano-metallic device with high conductance at the Fermi level and two sequential high on/off switching states. The origin of this property can be traced back to the existence of a HOMO which consists of two degenerate and asymmetric orbitals, lying close in energy to the Fermi level of the metallic leads. Their degeneracy is broken when the molecule is contacted to the leads, giving rise to two resonances which become pinned close to the Fermi level and display destructive interference.Comment: 4 pages, 4 figures. Reprinted (adapted) with permission from J. Am. Chem. Soc., 2013, 135 (6), 2052. Copyright 2013 American Chemical Societ

Planetary Nebulae as standard candles XI. Application to Spiral Galaxies

We report the results of an [O III] lambda 5007 survey for planetary nebulae (PN) in three spiral galaxies: M101 (NGC 5457), M51 (NGC 5194/5195) and M96 (NGC 3368). By comparing on-band/off-band [O III] lambda 5007 images with images taken in H-alpha and broadband R, we identify 65, 64 and 74 PN candidates in each galaxy, respectively. From these data, an adopted M31 distance of 770 kpc, and the empirical planetary nebula luminosity function (PNLF), we derive distances to M101, M51, and M96 of 7.7 +/- 0.5, 8.4 +/- 0.6, and 9.6 +/- 0.6 Mpc. These observations demonstrate that the PNLF technique can be successfully applied to late-type galaxies, and provide an important overlap between the Population I and Population II distance scales. We also discuss some special problems associated with using the PNLF in spiral galaxies, including the effects of dust and the possible presence of [O III] bright supernova remnants.Comment: 38 pages, TeX, with tables included but not figures. Uses epsf.tex and kpnobasic.tex. To be published in the Astophysical Journal. Full paper is available at http://www.astro.psu.edu/users/johnf/Text/research.htm

Topological Color Codes and Two-Body Quantum Lattice Hamiltonians

Topological color codes are among the stabilizer codes with remarkable properties from quantum information perspective. In this paper we construct a four-valent lattice, the so called ruby lattice, governed by a 2-body Hamiltonian. In a particular regime of coupling constants, degenerate perturbation theory implies that the low energy spectrum of the model can be described by a many-body effective Hamiltonian, which encodes the color code as its ground state subspace. The gauge symmetry $\mathbf{Z}_{2}\times\mathbf{Z}_{2}$ of color code could already be realized by identifying three distinct plaquette operators on the lattice. Plaquettes are extended to closed strings or string-net structures. Non-contractible closed strings winding the space commute with Hamiltonian but not always with each other giving rise to exact topological degeneracy of the model. Connection to 2-colexes can be established at the non-perturbative level. The particular structure of the 2-body Hamiltonian provides a fruitful interpretation in terms of mapping to bosons coupled to effective spins. We show that high energy excitations of the model have fermionic statistics. They form three families of high energy excitations each of one color. Furthermore, we show that they belong to a particular family of topological charges. Also, we use Jordan-Wigner transformation in order to test the integrability of the model via introducing of Majorana fermions. The four-valent structure of the lattice prevents to reduce the fermionized Hamiltonian into a quadratic form due to interacting gauge fields. We also propose another construction for 2-body Hamiltonian based on the connection between color codes and cluster states. We discuss this latter approach along the construction based on the ruby lattice.Comment: 56 pages, 16 figures, published version

Bottom-Up Synthesis of Polymeric Micro- and Nanoparticles with Regular Anisotropic Shapes

Shape-anisotropic polymeric micro- and nanoparticles are of significant interest for the development of novel composite materials, lock-and-key assemblies, and drug carriers. Currently, syntheses require external confinement in microfluidic devices or lithographic techniques associated with significant infrastructure and low productivity, so new methods are necessary to scale-up such production efficiently. Here we report bottom-up polymerization of regular shape-anisotropic particles (polygonal platelets with different numbers of edges, with and without protruding asperities, and fibrilar particles with controllable aspect ratios), with size control over 4 orders of magnitude (∼50 nm-1 mm). Polymerization also enables the study of much smaller shapes than could previously be studied in water suspensions, and we study the fundamental limits of the self-shaping transition process driving these transformations for monomer oil droplets of stearyl methacrylate (SMA) monomer oil. We show the method is compatible with a variety of polymerizing monomers and functional modifications of the particles (e.g., composites with magnetic nanoparticles, oil-soluble additives, etc.). We also describe postsynthetic surface modifications that lead to hierarchical superstructures. The synthesis procedure has great potential in efficient nanomanufacturing as it can achieve scalable production of the above shapes in a wide range of sizes, with minimum infrastructure and process requirements and little maintenance of the equipment

An Integral Methodology for Predicting Long Term RTN

Random Telegraph Noise (RTN) adversely impacts circuit performance and this impact increases for smaller devices and lower operation voltage. To optimize circuit design, many efforts have been made to model RTN. RTN is highly stochastic, with significant device-to-device variations. Early works often characterize individual traps first and then group them together to extract their statistical distributions. This bottom-up approach suffers from limitations in the number of traps it is possible to measure, especially for the capture and emission time constants, calling the reliability of extracted distributions into question. Several compact models have been proposed, but their ability to predict long term RTN is not verified. Many early works measured RTN only for tens of seconds, although a longer time window increases RTN by capturing slower traps. The aim of this work is to propose an integral methodology for modelling RTN and, for the first time, to verify its capability of predicting the long term RTN. Instead of characterizing properties of individual traps/devices, the RTN of multiple devices were integrated to form one dataset for extracting their statistical properties. This allows using the concept of effective charged traps (ECT) and transforms the need for time constant distribution to obtaining the kinetics of ECT, making long term RTN prediction similar to predicting ageing. The proposed methodology opens the way for assessing RTN impact within a window of 10 years by efficiently evaluating the probability of a device parameter at a given level

Current status of MELCOR 2.2 for fusion safety analyses

MELCOR is an integral code developed by Sandia National Laboratories (SNL) for the US Nuclear Regulatory Commission (USNRC) to perform severe accident analyses of Light Water Reactors (LWR). More recently, MELCOR capabilities are being extended also to analyze non-LWR fission technologies. Within the European MELCOR User Group (EMUG), organized in the framework of USNRC Cooperative Severe Accident Research Program (CSARP), an activity on the evaluation of the applicability of MELCOR 2.2 for fusion safety analyses has been launched and it has been coordinated by ENEA. The aim of the activity was to identify the physical models to be possibly implemented in MELCOR 2.2 necessary for fusion safety analyses, and to check if those models are already available in MELCOR 1.8.6 for fusion version, developed by Idaho National Laboratory (INL). From this activity, a list of modeling needs emerged from the safety analyses of fusion-related installations have been identified and described. Then, the importance of the various needs, intended as the priority for model implementation in the MELCOR 2.2 code, has been evaluated according to the technical expert judgement of the authors. In the present paper, the identified modeling needs are discussed. The ultimate goal would be to propose to have a single integrated MELCOR 2.2 code release capable to cover both fission and fusion applications

LHC Optics Measurement with Proton Tracks Detected by the Roman Pots of the TOTEM Experiment

Precise knowledge of the beam optics at the LHC is crucial to fulfil the physics goals of the TOTEM experiment, where the kinematics of the scattered protons is reconstructed with the near-beam telescopes -- so-called Roman Pots (RP). Before being detected, the protons' trajectories are influenced by the magnetic fields of the accelerator lattice. Thus precise understanding of the proton transport is of key importance for the experiment. A novel method of optics evaluation is proposed which exploits kinematical distributions of elastically scattered protons observed in the RPs. Theoretical predictions, as well as Monte Carlo studies, show that the residual uncertainty of this optics estimation method is smaller than 0.25 percent.Comment: 20 pages, 11 figures, 5 figures, to be submitted to New J. Phy

Current status of Melcor 2.2 for fusion safety analyses

MELCOR is an integral code developed by Sandia National Laboratories (SNL) for the US Nuclear Regulatory Commission (USNRC) to perform severe accident analyses of Light Water Reactors (LWR). More recently, MELCOR capabilities are being extended also to analyze non-LWR fission technologies. Within the European MELCOR User Group (EMUG), organized in the framework of the USNRC Cooperative Severe Accident Research Program (CSARP), an activity on the evaluation of the applicability of MELCOR 2.2 for fusion safety analyses has been launched and it has been coordinated by ENEA. The aim of the activity was to identify the physical models to be possibly implemented in MELCOR 2.2 necessary for fusion safety analyses, and to check if those models are already available in MELCOR 1.8.6 fusion version, developed by Idaho National Laboratory (INL). From this activity, a list of modeling needs that emerged from the safety analyses of fusion-related installations has been identified and described. Then, the importance of the various needs, intended as the priority for model implementation in the MELCOR 2.2 code, has been evaluated according to the technical expert judgment of the authors. In the present paper, the identified modeling needs are discussed. The ultimate goal would be to propose to have a single integrated MELCOR 2.2 code release capable to cover both fission and fusion applications