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Quantum computer

Tian Zhong, Jonathan M Kindem, Jake Rochman, Andrei Faraon
Ensembles of solid-state optical emitters enable broadband quantum storage and transduction of photonic qubits, with applications in high-rate quantum networks for secure communications and interconnecting future quantum computers. To transfer quantum states using ensembles, rephasing techniques are used to mitigate fast decoherence resulting from inhomogeneous broadening, but these techniques generally limit the bandwidth, efficiency and active times of the quantum interface. Here, we use a dense ensemble of neodymium rare-earth ions strongly coupled to a nanophotonic resonator to demonstrate a significant cavity protection effect at the single-photon level-a technique to suppress ensemble decoherence due to inhomogeneous broadening...
January 16, 2017: Nature Communications
Fabio Rizzo, Federico Polo, Gregorio Bottaro, Simona Fantacci, Sabrina Antonello, Lidia Armelao, Silvio Quici, Flavio Maran
We describe the synthesis, computational analysis, photophysics, electrochemistry and electrochemiluminescence (ECL) of a series of compounds formed of two triphenylamines linked by a fluorene or spirobifluorene bridge. The phenylamine moieties were modified at the para-position of the two external rings by electron-withdrawing or electron-donating substituents. These modifications allowed for fine tuning of the photoluminescence (PL) and ECL emission from blue to green, with an overall wavelength span of 73 (PL) and 67 (ECL) nm, respectively...
January 15, 2017: Journal of the American Chemical Society
Shuang Luo, Zongsu Wei, Richard Spinney, Zhihui Yang, Liyuan Chai, Ruiyang Xiao
In this study, a novel model based on aromatic meta-substituent grouping was presented to predict the second-order rate constants (k) for OH oxidation of PCBs in gas-phase. Since the oxidation kinetics are dependent on the chlorination degree and position, we hypothesized that it may be more accurate for k value prediction if we group PCB congeners based on substitution positions (i.e., ortho (o), meta (m), and para (p)). To test this hypothesis, we examined the correlation of polarizability (α), a quantum chemical based descriptor for k values, with an empirical Hammett constant (σ(+)) on each substitution position...
January 4, 2017: Chemosphere
Arjen J de Haas, Jos Oomens, Jordy Bouwman
Energetic processing of gaseous polycyclic aromatic hydrocarbons (PAHs) plays a pivotal role in the chemistries of inter- and circumstellar environments, certain planetary atmospheres, and also in the chemistry of combustion and soot formation. Although the precursor PAH species have been extensively characterized, the products from these gaseous breakdown reactions have received far less attention. It has been particularly challenging to accurately determine their molecular structure in gas-phase experiments, where comparisons against theoretical modeling are best made...
January 12, 2017: Physical Chemistry Chemical Physics: PCCP
Alexander A Tulub, Vassily E Stefanov
Despite the fact that DNA molecule is studied up and down, we know very little about the role of DNA triplets in coding amino acids and stop-codons. The paper aims to fill this gap through attracting spintronic ideas and carrying out QM/MM computations on a full-turn DNA fragment. The computations reveal two hidden symmetries: the spin splitting (the Rashba effect), confined within each triplet, and the quantum "phase" link between the triplet nature (in total, 64 triplets) and the corresponding amino acid and three stop-codons...
January 7, 2017: Journal of Theoretical Biology
Daniel Mann, Udo Höweler, Carsten Kötting, Klaus Gerwert
Time-resolved Fourier transform infrared (FTIR) spectroscopy is a powerful tool to elucidate label-free the reaction mechanisms of proteins. After assignment of the absorption bands to individual groups of the protein, the order of events during the reaction mechanism can be monitored and rate constants can be obtained. Additionally, structural information is encoded into infrared spectra and can be decoded by combining the experimental data with biomolecular simulations. We have determined recently the infrared vibrations of GTP and guanosine diphosphate (GDP) bound to Gαi1, a ubiquitous GTPase...
January 10, 2017: Biophysical Journal
Chien-Wei Fu, Thy-Hou Lin
As an important enzyme in Phase I drug metabolism, the flavin-containing monooxygenase (FMO) also metabolizes some xenobiotics with soft nucleophiles. The site of metabolism (SOM) on a molecule is the site where the metabolic reaction is exerted by an enzyme. Accurate prediction of SOMs on drug molecules will assist the search for drug leads during the optimization process. Here, some quantum mechanics features such as the condensed Fukui function and attributes from circular fingerprints (called Molprint2D) are computed and classified using the support vector machine (SVM) for predicting some potential SOMs on a series of drugs that can be metabolized by FMO enzymes...
2017: PloS One
Giacomo Prando
No abstract text is available yet for this article.
January 10, 2017: Nature Nanotechnology
G Thirunavukkarasu, M Mousley, M Babiker, J Yuan
Electron vortex beams constitute the first class of matter vortex beams which are currently routinely produced in the laboratory. Here, we briefly review the progress of this nascent field and put forward a natural quantum basis set which we show is suitable for the description of electron vortex beams. The normal modes are truncated Bessel beams (TBBs) defined in the aperture plane or the Fourier transform of the transverse structure of the TBBs (FT-TBBs) in the focal plane of a lens with the said aperture...
February 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
Rui-Jie Xue, Adam Grofe, He Yin, Zexing Qu, Jiali Gao, Hui Li
Linear and two-dimensional infrared (IR) spectroscopy of site-specific probe molecules provides an opportunity to gain a molecular-level understanding of the local hydrogen-bonding network, conformational dynamics, and long-range electrostatic interactions in condensed-phase and biological systems. A challenge in computation is to determine the time-dependent vibrational frequencies that incorporate explicitly both nuclear quantum effects of vibrational motions and an electronic structural representation of the potential energy surface...
January 10, 2017: Journal of Chemical Theory and Computation
Aurélien Moncomble, Jean-Paul Cornard, Michel Meyer
The stereochemical activity of the lone pair on Pb(II) complexes is assessed using several theoretical methods, including structural analyses, computations of Fukui functions, natural bond orbitals, electron localization function, investigation of the electron density and of its laplacian. The attention is focused on four octadentate N-carbamoylmethyl-substituted tetraazamacrocycles of various ring sizes ranging from 8 to 14 atoms associated with the Pb(II) cation. The theoretical study illustrates the geometrical constraints imposed by the ring structure which limits the spatial development of the lone pair but without fully preventing it...
January 2017: Journal of Molecular Modeling
Barbara Bellich, Silvia Di Fonzo, Letizia Tavagnacco, Marco Paolantoni, Claudio Masciovecchio, Federica Bertolotti, Giovanna Giannini, Rita De Zorzi, Silvano Geremia, Alessandro Maiocchi, Fulvio Uggeri, Norberto Masciocchi, Attilio Cesàro
The phenomenon of polymorphism is of great relevance in pharmaceutics, since different polymorphs have different physico-chemical properties, e.g. solubility, hence, bioavailability. Coupling diffractometric and spectroscopic experiments with thermodynamic analysis and computational work opens to a methodological approach which provides information on both structure and dynamics in the solid as well as in solution. The present work reports on the conformational changes in crystalline iopamidol, which is characterized by atropisomerism, a phenomenon that influences both the solution properties and the distinct crystal phases...
January 6, 2017: Molecular Pharmaceutics
Yoichi Miyahara, Antoine Roy-Gobeil, Peter Grutter
Electric charge detection by atomic force microscopy (AFM) with single-electron resolution (e-EFM) is a promising way to investigate the electronic level structure of individual quantum dots (QDs). The oscillating AFM tip modulates the energy of the QDs, causing single electrons to tunnel between QDs and an electrode. The resulting oscillating electrostatic force changes the resonant frequency and damping of the AFM cantilever, enabling electrometry with a single-electron sensitivity. Quantitative electronic level spectroscopy is possible by sweeping the bias voltage...
January 6, 2017: Nanotechnology
Carlos Marante, Markus Klinker, Inés Corral, Jesús González-Vázquez, Luca Argenti, Fernando Martín
The theoretical description of observables in attosecond pump-probe experiments requires a good representation of the system's ionization continuum. For polyelectronic molecules, however, this is still a challenge, due to the complicated short-range structure of correlated electronic wave functions. Whereas quantum chemistry packages (QCP) implementing sophisticated methods to compute bound electronic molecular states are well-established, comparable tools for the continuum are not widely available yet. To tackle this problem, we have developed a new approach that, by means of a hybrid Gaussian-B-spline basis, interfaces existing QCPs with close-coupling scattering methods...
January 6, 2017: Journal of Chemical Theory and Computation
Otoniel Denis-Alpizar, Raymond J Bemish, Markus Meuwly
The NO(X(2)Π) + N((4)S) reaction which occurs entirely in the triplet manifold of N2O is investigated using quasiclassical trajectories and quantum simulations. Fully-dimensional potential energy surfaces for the (3)A' and (3)A'' states are computed at the MRCI+Q level of theory and are represented using a reproducing kernel Hilbert space. The N-exchange and N2-formation channels are followed by using the multi-state adiabatic reactive molecular dynamics method. Up to 5000 K these reactions occur predominantly on the N2O (3)A'' surface...
January 6, 2017: Physical Chemistry Chemical Physics: PCCP
Walter M Weber, Thomas Mikolajick
Research in the field of electronics of one-dimensional group-IV semiconductor structures has attracted increasing attention over the past 15 years. The exceptional combination of the unique one-dimensional electronic transport properties with the mature material know-how of highly integrated silicon and germanium technology holds the promise of enhancing state-of-the-art electronics. In addition of providing conduction channels that can bring conventional field effect transistors to the uttermost scaling limits, the physics of 1-D group IV nanowires endows new device principles...
January 5, 2017: Reports on Progress in Physics
Jan H Jensen, Christopher J Swain, Lars Olsen
Rapid yet accurate pKa prediction for druglike molecules is a key challenge in computational chemistry. This study uses PM6-DH+/COSMO, PM6/COSMO, PM7/COSMO, PM3/COSMO, AM1/COSMO, PM3/SMD, AM1/SMD, and DFTB3/SMD to predict the pKa values of 53 amine groups in 48 druglike compounds. The approach uses an isodesmic reaction where the pKa value is computed relative to a chemically related reference compound for which the pKa value has been measured experimentally or estimated using a standard empirical approach...
January 12, 2017: Journal of Physical Chemistry. A
Davide Castelvecchi
No abstract text is available yet for this article.
January 3, 2017: Nature
Sebastian P Sitkiewicz, Josep M Oliva, Juan Z Dávalos, Rafael Notario, Alfonso Saiz-Lopez, Diego R Alcoba, Ofelia B Oña, Daniel Roca-Sanjuán
The electronic states of atmospheric relevant molecules IBr and HgBr2 are reported, within the UV-Vis spectrum range (170nm≤λphoton≤600 nm) by means of the complete-active-space self-consistent field/multi-state complete-active-space second-order perturbation theory/spin-orbit restricted-active-space state-interaction (CASSCF/MS-CASPT2/SO-RASSI) quantum-chemical approach and atomic-natural-orbital relativistic-correlation-consistent (ANO-RCC) basis sets. Several analyses of the methodology were carried out in order to reach converged results and therefore to establish a highly accurate level of theory...
December 28, 2016: Journal of Chemical Physics
M Myronakis, J Rottmann, Y Hu, A Wang, D Shedlock, D Morf, J Star-Lack, R Berbeco
PURPOSE: To develop and validate a Monte Carlo (MC) model of a novel multi-layer imager (MLI) for megavolt (MV) energy beams. The MC model will enable performance optimization of the MLI design for clinical applications including patient setup verification, tumor tracking and MVCBCT. METHODS: The MLI is composed of four layers of converter, scintillator and light detector, each layer similar to the current clinical AS1200 detector (Varian Medical Systems, Inc). The MLI model was constructed using the Geant4 Application for Tomographic Emission (GATE v7...
June 2016: Medical Physics
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