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Quantum computer

Partha Pratim Pal, S Ramakrishna, Tamar Seideman
The Landauer expression for computing current-voltage characteristics in nanoscale devices is efficient but not suited to transient phenomena and a time-dependent current because it is applicable only when the charge carriers transition into a steady flux after an external perturbation. In this article, we construct a very general expression for time-dependent current in an electrode-molecule-electrode arrangement. Utilizing a model Hamiltonian (consisting of the subsystem energy levels and their electronic coupling terms), we propagate the Schrödinger wave function equation to numerically compute the time-dependent population in the individual subsystems...
April 14, 2018: Journal of Chemical Physics
Jerzy Cioslowski, Krzysztof Strasburger
Electronic properties of several states of the five- and six-electron harmonium atoms are obtained from large-scale calculations employing explicitly correlated basis functions. The high accuracy of the computed energies (including their components), natural spinorbitals, and their occupation numbers makes them suitable for testing, calibration, and benchmarking of approximate formalisms of quantum chemistry and solid state physics. In the case of the five-electron species, the availability of the new data for a wide range of the confinement strengths ω allows for confirmation and generalization of the previously reached conclusions concerning the performance of the presently known approximations for the electron-electron repulsion energy in terms of the 1-matrix that are at heart of the density matrix functional theory (DMFT)...
April 14, 2018: Journal of Chemical Physics
Richard Y Li, Rosa Di Felice, Remo Rohs, Daniel A Lidar
Transcription factors regulate gene expression, but how these proteins recognize and specifically bind to their DNA targets is still debated. Machine learning models are effective means to reveal interaction mechanisms. Here we studied the ability of a quantum machine learning approach to predict binding specificity. Using simplified datasets of a small number of DNA sequences derived from actual binding affinity experiments, we trained a commercially available quantum annealer to classify and rank transcription factor binding...
2018: NPJ quantum information
Imam Makhfudz
We propose in this work an effective field theory description of the chiral spin liquid state in Heisenberg spin system on kagom\'{e} lattice.To this end, we derive the low-energy effective theory of kagom\'{e} (isotropic) Heisenberg antiferromagnet around its ordered ground states found numerically and show that quantum fluctuations induced by further neighbor spin exchanges are equally strong as those from first neighbor.We use a chiral order parameter theory to argue for the occurrence of finite temperature chiral symmetry breaking transition into chiral ordered state in kagom\'{e} antiferromagnet with further neighbor spin exchange interactions...
April 13, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
C Neill, P Roushan, K Kechedzhi, S Boixo, S V Isakov, V Smelyanskiy, A Megrant, B Chiaro, A Dunsworth, K Arya, R Barends, B Burkett, Y Chen, Z Chen, A Fowler, B Foxen, M Giustina, R Graff, E Jeffrey, T Huang, J Kelly, P Klimov, E Lucero, J Mutus, M Neeley, C Quintana, D Sank, A Vainsencher, J Wenner, T C White, H Neven, J M Martinis
A key step toward demonstrating a quantum system that can address difficult problems in physics and chemistry will be performing a computation beyond the capabilities of any classical computer, thus achieving so-called quantum supremacy. In this study, we used nine superconducting qubits to demonstrate a promising path toward quantum supremacy. By individually tuning the qubit parameters, we were able to generate thousands of distinct Hamiltonian evolutions and probe the output probabilities. The measured probabilities obey a universal distribution, consistent with uniformly sampling the full Hilbert space...
April 13, 2018: Science
Y Cao, G C Wang, H D Liu, C F Sun
The Toffoli gate (controlled-controlled-NOT gate) is one typical three-qubit gate, it plus a Hadamard gate form a universal set of gates in quantum computation. We present an efficient method to implement the Toffoli gate using an array of coupled cavities with one three-level atom in each cavity. The large detuning between atoms and classical (quantum) fields plays an important role and the gate is implemented in one-step. The quantum information is encoded into the low-lying states of identical atoms and it is convenient to address qubit individually...
April 11, 2018: Scientific Reports
Yangchao Shen, Yao Lu, Kuan Zhang, Junhua Zhang, Shuaining Zhang, Joonsuk Huh, Kihwan Kim
Molecules are one of the most demanding quantum systems to be simulated by quantum computers due to their complexity and the emergent role of quantum nature. The recent theoretical proposal of Huh et al. (Nature Photon., 9, 615 (2015)) showed that a multi-photon network with a Gaussian input state can simulate a molecular spectroscopic process. Here, we present the first quantum device that generates a molecular spectroscopic signal with the phonons in a trapped ion system, using SO2 as an example. In order to perform reliable Gaussian sampling, we develop the essential experimental technology with phonons, which includes the phase-coherent manipulation of displacement, squeezing, and rotation operations with multiple modes in a single realization...
January 28, 2018: Chemical Science
Gareth W Richings, Scott Habershon
We present significant algorithmic improvements to a recently proposed direct quantum dynamics method, based upon combining well established grid-based quantum dynamics approaches and expansions of the potential energy operator in terms of a weighted sum of Gaussian functions. Specifically, using a sum of low-dimensional Gaussian functions to represent the potential energy surface (PES), combined with a secondary fitting of the PES using singular value decomposition, we show how standard grid-based quantum dynamics methods can be dramatically accelerated without loss of accuracy...
April 7, 2018: Journal of Chemical Physics
Wenxiang Hu, Bing Gu, Ignacio Franco
Electronic decoherence processes in molecules and materials are usually thought and modeled via schemes for the system-bath evolution in which the bath is treated either implicitly or approximately. Here we present computations of the electronic decoherence dynamics of a model many-body molecular system described by the Su-Schrieffer-Heeger Hamiltonian with Hubbard electron-electron interactions using an exact method in which both electronic and nuclear degrees of freedom are taken into account explicitly and fully quantum mechanically...
April 7, 2018: Journal of Chemical Physics
Sergio Menta, Alessia Ciogli, Claudio Villani, Francesco Gasparrini, Marco Pierini
Argentation chromatography is widely used nowadays as a powerful tool to separate complex mixtures of analytes containing unsaturated and/or aromatic fragments. Here we present the results of chromatographic and computational studies on a silver-thiolate stationary phase, in which the silver metal is covalently bonded to mercaptopropyl silica particles. The exceptionally high selectivity displayed by this organometallic moiety prompted us to deeply investigate its molecular recognition properties. The interactions of the silver atom with a series of benzene derivatives was investigated to gain information on the mechanism by which the different ring substituents modulate retention factors and selectivity...
August 17, 2018: Analytica Chimica Acta
Elisa Liberatore, Rocco Meli, Ursula Rothlisberger
We present here our implementation of a time-reversible, multiple time step (MTS) method for full QM and hybrid QM/MM Born-Oppenheimer molecular dynamics simulations. The method relies on a fully flexible combination of electronic structure methods - from Density Functional Theory to wavefunction-based quantum chemistry methods - to evaluate the nuclear forces in the reference and in the correction steps. The possibility of combining different electronic structure methods is based on the observation that exchange and correlation terms only contribute to the low-frequency modes of nuclear forces...
April 6, 2018: Journal of Chemical Theory and Computation
Jianbo Li, Xiao-Long Tan, Jin-Hong Ma, Si-Qing Xu, Zhi-Wei Kuang, Shan Liang, Si Xiao, Meng-Dong He, Nam-Chol Kim, Jian-Hua Luo, Li-Qun Chen
We present a study for the impact of exciton-phonon and exciton-plasmon interactions on bistable four-wave mixing (FWM) signals in a metal nanoparticle -monolayer MoS2 nanoresonator hybrid system. Via tracing the FWM response we predict that, depending on the excitation conditions and the system parameters, such a system exhibits "U-shaped" bistable FWM signals. We also map out bistability phase diagrams within the system's parameter space. Especially, we show that compared with the exciton-phonon interaction, a strong exciton-plasmon interaction plays a dominate role in the generation of optical bistability, and the bistable region will be greatly broadened by shortening the distance between the metal nanoparticle and the monolayer MoS2 nanoresonator...
April 5, 2018: Nanotechnology
Jia Zhou, Xiaofeng Zhen
An efficient and economical way to tune the properties of two-dimensional (2D) materials is by forming van der Waals (vdW) hetero-layered structures in order to achieve a better performance in energy-related applications. In this theoretical work, we employ first-principles calculations to investigate a novel tetragonal (t-)ZnS/ZnSe hetero-bilayer (BL), as well as bilayers of ZnS and ZnSe only. A significant quantum confinement effect has been observed for all bilayers by state-of-the-art computations based upon the quasiparticle G0W0 approach and the Bethe-Salpeter equation (BSE)...
April 5, 2018: Physical Chemistry Chemical Physics: PCCP
Florian Häse, Christoph Kreisbeck, Alán Aspuru-Guzik
Understanding the relationship between the structure of light-harvesting systems and their excitation energy transfer properties is of fundamental importance in many applications including the development of next generation photovoltaics. Natural light harvesting in photosynthesis shows remarkable excitation energy transfer properties, which suggests that pigment-protein complexes could serve as blueprints for the design of nature inspired devices. Mechanistic insights into energy transport dynamics can be gained by leveraging numerically involved propagation schemes such as the hierarchical equations of motion (HEOM)...
December 1, 2017: Chemical Science
Martha Y Suárez-Villagrán, Ricardo B R Azevedo, John H Miller
Biases in mutation rate can influence molecular evolution, yielding rates of evolution that vary widely in different parts of the genome and even among neighboring nucleotides. Here, we explore one possible mechanism of influence on sequence-specific mutation rates, the electron-hole, which can localize and potentially trigger a replication mismatch. A hole is a mobile site of positive charge created during one-electron oxidation by, for example, radiation, contact with a mutagenic agent, or oxidative stress...
April 1, 2018: Genome Biology and Evolution
Xianwei Wang, Yang Li, Ya Gao, Zejin Yang, Chenhui Lu, Tong Zhu
An efficient computational approach for modeling protein electrostatic is developed according to static point-charge model distributions based on the linear-scaling EE-GMFCC (electrostatically embedded generalized molecular fractionation with conjugate caps) quantum mechanical (QM) method. In this approach, the Electrostatic-Potential atomic charges are obtained from ab initio calculation of protein, both polarization and charge transfer effect are taken into consideration. This approach shows a significant improvement in the description of electrostatic potential and solvation energy of proteins comparing with current popular molecular mechanics (MM) force fields...
April 3, 2018: Scientific Reports
Mingsen Pan, Han Zhao, Pei Miao, Stefano Longhi, Liang Feng
Zero-energy particles (such as Majorana fermions) are newly predicted quasiparticles and are expected to play an important role in fault-tolerant quantum computation. In conventional Hermitian quantum systems, however, such zero states are vulnerable and even become vanishing if couplings with surroundings are of the same topological nature. Here we demonstrate a robust photonic zero mode sustained by a spatial non-Hermitian phase transition in a parity-time (PT) symmetric lattice, despite the same topological order across the entire system...
April 3, 2018: Nature Communications
Matthew R Ross, Amity Andersen, Zachary W Fox, Yu Zhang, Kiryong Hong, Jae-Hyuk Lee, Amy A Cordones, Anne M March, Gilles Doumy, Stephen H Southworth, Matthew A Marcus, Robert W Schoenlein, Shaul Mukamel, Niranjan Govind, Munira Khalil
We present a joint experimental and computational study of the hexacyanoferrate aqueous complexes at equilibrium in the 250 meV to 7.15 keV regime. The experiments and the computations include the vibrational spectroscopy of the cyanide ligands, the valence electronic absorption spectra and Fe 1s core hole spectra using element-specific resonant X-ray absorption and emission techniques. Density functional theory (DFT) based quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations are performed to generate explicit solute-solvent configurations, which serve as inputs for the spectroscopy calculations of the experiments spanning the IR to X-ray wavelengths...
April 3, 2018: Journal of Physical Chemistry. B
Mathias S Scheurer, Shubhayu Chatterjee, Wei Wu, Michel Ferrero, Antoine Georges, Subir Sachdev
We compute the electronic Green's function of the topologically ordered Higgs phase of a SU(2) gauge theory of fluctuating antiferromagnetism on the square lattice. The results are compared with cluster extensions of dynamical mean field theory, and quantum Monte Carlo calculations, on the pseudogap phase of the strongly interacting hole-doped Hubbard model. Good agreement is found in the momentum, frequency, hopping, and doping dependencies of the spectral function and electronic self-energy. We show that lines of (approximate) zeros of the zero-frequency electronic Green's function are signs of the underlying topological order of the gauge theory and describe how these lines of zeros appear in our theory of the Hubbard model...
April 2, 2018: Proceedings of the National Academy of Sciences of the United States of America
Saeed Amini Komijani
Importance of 2'-deoxyguanosine-uridine mispair as the most occurring mismatch in transcriptional studies of RNAs from DNAs is multiplied when 5-halo-substituted uridine species cause to serious increase in probability of its occurrence. Many studies relate this higher probability to existence of possible tautomeric and ionic forms of its constituent bases. According to these statements, relative populations of mismatches between 5-fluorouridine and both keto and enol forms of 2'-deoxyguanosine are computed by using conformational search...
April 2, 2018: Journal of Physical Chemistry. B
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