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Quantum computer

Bi-Heng Liu, Xiao-Min Hu, Jiang-Shan Chen, Yun-Feng Huang, Yong-Jian Han, Chuan-Feng Li, Guang-Can Guo, Adán Cabello
We experimentally show that nonlocality can be produced from single-particle contextuality by using two-particle correlations which do not violate any Bell inequality by themselves. This demonstrates that nonlocality can come from an a priori different simpler phenomenon, and connects contextuality and nonlocality, the two critical resources for, respectively, quantum computation and secure communication. From the perspective of quantum information, our experiment constitutes a proof of principle that quantum systems can be used simultaneously for both quantum computation and secure communication...
November 25, 2016: Physical Review Letters
Peng Zou, Joachim Brand, Xia-Ji Liu, Hui Hu
We investigate traveling solitons of a one- or two-dimensional spin-orbit-coupled Fermi superfluid in both topologically trivial and nontrivial regimes by solving the static and time-dependent Bogoliubov-de Gennes equations. We find a critical velocity v_{h} for traveling solitons that is much smaller than the value predicted using the Landau criterion due to spin-orbit coupling. Above v_{h}, our time-dependent simulations in harmonic traps indicate that traveling solitons decay by radiating sound waves. In the topological phase, we predict the existence of peculiar Majorana solitons, which host two Majorana fermions and feature a phase jump of π across the soliton, irrespective of the velocity of travel...
November 25, 2016: Physical Review Letters
S Weidt, J Randall, S C Webster, K Lake, A E Webb, I Cohen, T Navickas, B Lekitsch, A Retzker, W K Hensinger
Trapped ions are a promising tool for building a large-scale quantum computer. However, the number of required radiation fields for the realization of quantum gates in any proposed ion-based architecture scales with the number of ions within the quantum computer, posing a major obstacle when imagining a device with millions of ions. Here, we present a fundamentally different approach for trapped-ion quantum computing where this detrimental scaling vanishes. The method is based on individually controlled voltages applied to each logic gate location to facilitate the actual gate operation analogous to a traditional transistor architecture within a classical computer processor...
November 25, 2016: Physical Review Letters
Panagiotis Botsinis, Zunaira Babar, Dimitrios Alanis, Daryus Chandra, Hung Nguyen, Soon Xin Ng, Lajos Hanzo
When quantum computing becomes a wide-spread commercial reality, Quantum Search Algorithms (QSA) and especially Grover's QSA will inevitably be one of their main applications, constituting their cornerstone. Most of the literature assumes that the quantum circuits are free from decoherence. Practically, decoherence will remain unavoidable as is the Gaussian noise of classic circuits imposed by the Brownian motion of electrons, hence it may have to be mitigated. In this contribution, we investigate the effect of quantum noise on the performance of QSAs, in terms of their success probability as a function of the database size to be searched, when decoherence is modelled by depolarizing channels' deleterious effects imposed on the quantum gates...
December 7, 2016: Scientific Reports
Andrea Zen, Loïc M Roch, Stephen J Cox, Xiao Liang Hu, Sandro Sorella, Dario Alfè, Angelos Michaelides
Clay minerals are ubiquitous in nature, and the manner in which they interact with their surroundings has important industrial and environmental implications. Consequently, a molecular-level understanding of the adsorption of molecules on clay surfaces is crucial. In this regard computer simulations play an important role, yet the accuracy of widely used empirical force fields (FF) and density functional theory (DFT) exchange-correlation functionals is often unclear in adsorption systems dominated by weak interactions...
November 23, 2016: Journal of Physical Chemistry. C, Nanomaterials and Interfaces
Ahmed Taki Eddine Ardjani, Sidi Mohamed Mekelleche
In the present work, the molecular structure and the antioxidant activity of 4-(5-chloro-2-hydroxyphenylamino)-4-oxobut-2-enoic acid (A) and its derivatives (B-E) have been studied at the B3LYP/6-31++G(2d,2p) computational level. The obtained results indicate that the hydrogen atom transfer (HAT mechanism) is thermodynamically more favored in gas phase; whereas, the sequential proton loss-electron transfer (SPLET mechanism) is more preferred in polar solvents. The antioxidant activity of compounds A-E is also analyzed by the calculation of atomic spin densities, chemical hardnesses, dipole moments, and lipophilicity indexes...
December 2016: Journal of Molecular Modeling
Adegoke Ojewole, Anna Lowegard, Pablo Gainza, Stephanie M Reeve, Ivelin Georgiev, Amy C Anderson, Bruce R Donald
Drug resistance in protein targets is an increasingly common phenomenon that reduces the efficacy of both existing and new antibiotics. However, knowledge of future resistance mutations during pre-clinical phases of drug development would enable the design of novel antibiotics that are robust against not only known resistant mutants, but also against those that have not yet been clinically observed. Computational structure-based protein design (CSPD) is a transformative field that enables the prediction of protein sequences with desired biochemical properties such as binding affinity and specificity to a target...
2017: Methods in Molecular Biology
Fabian Ewert, Marcel Bergmann, Peter van Loock
We propose a projection measurement onto encoded Bell states with a static network of linear optical elements. By increasing the size of the quantum error correction code, both Bell measurement efficiency and photon-loss tolerance can be made arbitrarily high at the same time. As a main application, we show that all-optical quantum communication over large distances with communication rates similar to those of classical communication is possible solely based on local state teleportations using optical sources of encoded Bell states, fixed arrays of beam splitters, and photon detectors...
November 18, 2016: Physical Review Letters
Piotr Tourkine, Pierre Vanhove
The monodromy relations in string theory provide a powerful and elegant formalism to understand some of the deepest properties of tree-level field theory amplitudes, like the color-kinematics duality. This duality has been instrumental in tremendous progress on the computations of loop amplitudes in quantum field theory, but a higher-loop generalization of the monodromy construction was lacking. In this Letter, we extend the monodromy relations to higher loops in open string theory. Our construction, based on a contour deformation argument of the open string diagram integrands, leads to new identities that relate planar and nonplanar topologies in string theory...
November 18, 2016: Physical Review Letters
M F Brandl, M W van Mourik, L Postler, A Nolf, K Lakhmanskiy, R R Paiva, S Möller, N Daniilidis, H Häffner, V Kaushal, T Ruster, C Warschburger, H Kaufmann, U G Poschinger, F Schmidt-Kaler, P Schindler, T Monz, R Blatt
We report on the design of a cryogenic setup for trapped ion quantum computing containing a segmented surface electrode trap. The heat shield of our cryostat is designed to attenuate alternating magnetic field noise, resulting in 120 dB reduction of 50 Hz noise along the magnetic field axis. We combine this efficient magnetic shielding with high optical access required for single ion addressing as well as for efficient state detection by placing two lenses each with numerical aperture 0.23 inside the inner heat shield...
November 2016: Review of Scientific Instruments
Deacon J Nemchick, Michael K Cohen, Patrick H Vaccaro
The near-ultraviolet π(*)←π absorption system of weakly bound complexes formed between tropolone (TrOH) and formic acid (FA) under cryogenic free-jet expansion conditions has been interrogated by exploiting a variety of fluorescence-based laser-spectroscopic probes, with synergistic quantum-chemical calculations built upon diverse model chemistries being enlisted to unravel the structural and dynamical properties of the pertinent ground [X̃(1)A(')] and excited [Ã(1)A(')π(*)π] electronic states. For binary TrOH ⋅ FA adducts, the presence of dual hydrogen-bond linkages gives rise to three low-lying isomers designated (in relative energy order) as INT, EXT1, and EXT2 depending on whether docking of the FA ligand to the TrOH substrate takes place internal or external to the five-membered reaction cleft of tropolone...
November 28, 2016: Journal of Chemical Physics
Yong Siah Teo, Dmitri Mogilevtsev, Alexander Mikhalychev, Jaroslav Řeháček, Zdeněk Hradil
In continuous-variable tomography, with finite data and limited computation resources, reconstruction of a quantum state of light is performed on a finite-dimensional subspace. In principle, the data themselves encode all information about the relevant subspace that physically contains the state. We provide a straightforward and numerically feasible procedure to uniquely determine the appropriate reconstruction subspace by extracting this information directly from the data for any given unknown quantum state of light and measurement scheme...
December 1, 2016: Scientific Reports
Jaap E Borger, Andreas W Ehlers, Martin Lutz, J Chris Slootweg, Koop Lammertsma
Two [3+1] fragmentations of the Lewis acid stabilized bicyclo[1.1.0]tetraphosphabutanide Li[Mes*P4 ⋅ BPh3 ] (Mes*=2,4,6-tBu3 C6 H2 ) are reported. The reactions proceed by extrusion of a P1 fragment, induced by either an imidazolium salt or phenylisocyanate, with release of the transient triphosphirene Mes*P3 , which was isolated as a dimer and trapped by 1,3-cyclohexadiene as a Diels-Alder adduct. DFT quantum chemical computations were used to delineate the reaction mechanisms. These unprecedented pathways grant access to both P1 - and P3 -containing organophosphorus compounds in two simple steps from white phosphorus...
November 30, 2016: Angewandte Chemie
Behnam Nikoobakht
The (2)T2g ← (1)A1g photo-electron spectrum of octahedral tungsten hexacarbonyl W(CO)6 is investigated quantum dynamically. The photo-electron spectrum is calculated by construction of a model Hamiltonian in which the T2g ⊗ (2a1g ⊕ 2eg ⊕ 2t2g) Jahn-Teller (JT) problem up to second-order vibronic coupling (including all possible bilinear terms) together with the spin-orbit (SO) coupling up to the zeroth-order SO splitting is treated. A computational method was suggested to generate all vibronic coupling parameters of the Hamiltonian model and potential energy surfaces (PESs) based on fitting of the minimum eigenvalue of the Hamiltonian model to the adiabatic energies of the energetically lowest branch of the (2)T2g electronic state of W(CO)6(+)˙...
November 29, 2016: Physical Chemistry Chemical Physics: PCCP
Clemens Schäfermeier, Hugo Kerdoncuff, Ulrich B Hoff, Hao Fu, Alexander Huck, Jan Bilek, Glen I Harris, Warwick P Bowen, Tobias Gehring, Ulrik L Andersen
Laser cooling is a fundamental technique used in primary atomic frequency standards, quantum computers, quantum condensed matter physics and tests of fundamental physics, among other areas. It has been known since the early 1990s that laser cooling can, in principle, be improved by using squeezed light as an electromagnetic reservoir; while quantum feedback control using a squeezed light probe is also predicted to allow improved cooling. Here we show the implementation of quantum feedback control of a micro-mechanical oscillator using squeezed probe light...
November 29, 2016: Nature Communications
Jia Wang, Lee-Ming Cheng, Tong Su
Designing secure and efficient multivariate public key cryptosystems [multivariate cryptography (MVC)] to strengthen the security of RSA and ECC in conventional and quantum computational environment continues to be a challenging research in recent years. In this paper, we will describe multivariate public key cryptosystems based on extended Clipped Hopfield Neural Network (CHNN) and implement it using the MVC (CHNN-MVC) framework operated in GF(p) space. The Diffie--Hellman key exchange algorithm is extended into the matrix field, which illustrates the feasibility of its new applications in both classic and postquantum cryptography...
November 23, 2016: IEEE Transactions on Neural Networks and Learning Systems
Aravindhan Ganesan, Michelle L Coote, Khaled Barakat
Given the significant time and financial costs of developing a commercial drug, it remains important to constantly reform the drug discovery pipeline with novel technologies that can narrow the candidates down to the most promising lead compounds for clinical testing. The past decade has witnessed tremendous growth in computational capabilities that enable in silico approaches to expedite drug discovery processes. Molecular dynamics (MD) has become a particularly important tool in drug design and discovery...
November 24, 2016: Drug Discovery Today
Jose Luis Rosales, Vicente Martin
Feynman's prescription for a quantum simulator was to find a Hamitonian for a system that could serve as a computer. The Pólya-Hilbert conjecture proposed the demonstration of Riemann's hypothesis through the spectral decomposition of Hermitian operators. Here we study the problem of decomposing a number into its prime factors, N=xy, using such a simulator. First, we derive the Hamiltonian of the physical system that simulates a new arithmetic function formulated for the factorization problem that represents the energy of the computer...
November 11, 2016: Physical Review Letters
Behnoosh Sadeghi Moghadam, Mohammad Razmkhah, Mohammad Taghi Hamed Mosavian, Fatemeh Moosavi
Electric double layer (EDL) supercapacitors, using ionic liquid electrolytes, have been receiving a great deal of attention in response to the growing demand for energy storage systems. In the present study, the nanoscopic structure of amino acid ionic liquids (AAILs) as biodegradable electrolytes near a neutral graphene surface was studied by molecular dynamics (MD) simulation. In order to explore the influence of the anion type and structure, the effect of the alkyl side-chain length of amino acids on the EDL was investigated...
November 25, 2016: Physical Chemistry Chemical Physics: PCCP
Thanja Lamberts, Pradipta Kumar Samanta, Andreas Köhn, Johannes Kästner
The final step of the water formation network on interstellar grain surfaces starting from the H + O2 route is the reaction between H and H2O2. This reaction is known to have a high activation energy and therefore at low temperatures it can only proceed via tunneling. To date, however, no rate constants are available at temperatures below 200 K. In this work, we use instanton theory to compute rate constants for the title reaction with and without isotopic substitutions down to temperatures of 50 K. The calculations are based on density functional theory, with additional benchmarks for the activation energy using unrestricted single-reference and multireference coupled-cluster single-point energies...
November 25, 2016: Physical Chemistry Chemical Physics: PCCP
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