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Quantum physics

Ling-Na Wu, Xin-Yu Luo, Zhi-Fang Xu, Masahito Ueda, Ruquan Wang, L You
Spin-orbit coupling (SOC) plays an essential role in many exotic and interesting phenomena in condensed matter physics. In neutral-atom-based quantum simulations, synthetic SOC constitutes a key enabling element. The strength of SOC realized so far is limited by various reasons or constraints. This work reports tunable SOC synthesized with a gradient magnetic field (GMF) for atoms in a harmonic trap. Nearly ten-fold enhancement is observed when the GMF is modulated near the harmonic-trap resonance in comparison with the free-space situation...
April 27, 2017: Scientific Reports
Sudipta Kumar Sinha, Mohit Mehta, Sandeep Patel
Conventional classical force fields by construction do not explicitly partition intermolecular interactions to include polarization and charge transfer effects, whereas fully quantum mechanical treatments allow a means to effect this dissection (although not uniquely due to the lack of a charge transfer operator). Considering the importance of polarization in a variety of systems, a particular class of classical models, charge equilibration models, have been extensively developed to study those systems; since these types of interaction models are inherently based on movement of charge throughout a system, they are natural platform for including polarization and charge transfer effects within the context of molecular simulations...
June 15, 2017: Journal of Computational Chemistry
Naofumi Abe, Yasuyoshi Mitsumori, Mark Sadgrove, Keiichi Edamatsu
Polarization is one of the fundamental properties of light, providing numerous applications in science and technology. While 'dynamically unpolarized' single-photon sources are demanded for various quantum applications, such sources have never been explored. Here we demonstrate dynamically unpolarized single-photon emission from a single [111]-oriented nitrogen- vacancy centre in diamond, in which the single-photon stream is unpolarized, exhibiting intrinsic randomness with vanishing polarization correlation between time adjacent photons...
April 26, 2017: Scientific Reports
Yuan Cao, Yu-Huai Li, Zhu Cao, Juan Yin, Yu-Ao Chen, Hua-Lei Yin, Teng-Yun Chen, Xiongfeng Ma, Cheng-Zhi Peng, Jian-Wei Pan
Intuition from our everyday lives gives rise to the belief that information exchanged between remote parties is carried by physical particles. Surprisingly, in a recent theoretical study [Salih H, Li ZH, Al-Amri M, Zubairy MS (2013) Phys Rev Lett 110:170502], quantum mechanics was found to allow for communication, even without the actual transmission of physical particles. From the viewpoint of communication, this mystery stems from a (nonintuitive) fundamental concept in quantum mechanics-wave-particle duality...
April 25, 2017: Proceedings of the National Academy of Sciences of the United States of America
K Krieger, P Elliott, T Müller, N Singh, J K Dewhurst, E K U Gross, S Sharma
We report ab initio simulations of the quantum dynamics of electronic charge and spins when subjected to intense laser pulses. By performing these purely electron-dynamics calculations for a thin film and for the bulk of Ni, we conclude that formation of surfaces has a dramatic influence of amplifying the laser induced demagnetization. The reason for this amplification is enhanced spin-currents on the surface of the thin films. We show that the underlying physics of demagnetization for bulk is dominated by spin-flips induced by spin-orbit coupling...
April 25, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Barbara Fresch, Francoise Remacle, Raphael D Levine
The implementation of probabilistic algorithms by deterministic hardware is demanding and requires hundreds of instructions to generate pseudo-random sequence of numbers. On the contrary, the dynamics at the molecular scale is physically governed by probabilistic laws because of the stochastic nature of thermally activated and quantum processes. By simulating the exciton transfer dynamics in a multi chromophoric system we demonstrate the implementation of a random walk that samples the possible pathways of a traveler through a network and can be probed by time resolved fluorescence spectroscopy...
April 25, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Francis G Woodhouse, Jörn Dunkel
Chemically or optically powered active matter plays an increasingly important role in materials design, but its computational potential has yet to be explored systematically. The competition between energy consumption and dissipation imposes stringent physical constraints on the information transport in active flow networks, facilitating global optimization strategies that are not well understood. Here, we combine insights from recent microbial experiments with concepts from lattice-field theory and non-equilibrium statistical mechanics to introduce a generic theoretical framework for active matter logic...
April 25, 2017: Nature Communications
Dongil Chu, Young Hee Lee, Eun Kyu Kim
Recent discoveries in the field of two-dimensional (2D) materials have led to the demonstration of exotic devices. Although they have new potential applications in electronics, thermally activated transport over a metal/semiconductor barrier sets physical subthermionic limitations. The challenge of realizing an innovative transistor geometry that exploits this concern remains. A new class of 2D assembly (namely, "carristor") with a configuration similar to the metal-insulator-semiconductor structure is introduced in this work...
April 2017: Science Advances
Marco Mendolicchio, Emanuele Penocchio, Daniele Licari, Nicola Tasinato, Vincenzo Barone
The determination of accurate equilibrium molecular structures plays a fundamental role for understanding many physical-chemical properties of molecules, ranging from the precise evaluation of the electronic structure to the analysis of dynamical and environmental effects in tuning their overall behavior. For this purpose the so-called semi-experimental approach, based on a non-linear least-squares fit of the moments of inertia associated to a set of available isotopologues, allows one to obtain very accurate results, without the unfavorable computational cost characterizing high-level quantum chemical methods...
April 24, 2017: Journal of Chemical Theory and Computation
Elad Harel
The correlations between different quantum-mechanical degrees of freedom of molecular species dictate their chemical and physical properties. Generally, these correlations are reflected in the optical response of the system but in low-order or low-dimensionality measurement the signals are highly averaged. Here, we describe a novel four-dimensional coherent spectroscopic method that directly correlates within and between the manifold of electronic and vibrational states. The optical response theory is developed in terms of both resonant and non-resonant field-matter interactions...
April 21, 2017: Journal of Chemical Physics
Agnieszka Roztoczyńska, Paweł Lipkowski, Justyna Kozłowska, Wojciech Bartkowiak
Nowadays, much attention is put toward the description of noncovalent complexes exposed to the high pressure or embedded in confining environments. Such conditions may strongly modify the physical and chemical properties of molecular systems. This study focuses on the theoretical description of the confinement induced changes in geometry and energetic parameters of the halogen bonded FCl⋯CNF complex. A model analytical potential is applied to render the effect of orbital compression. In order to analyze the nature of halogen bond interaction, in the presence of spatial confinement, the supermolecular approach together with the symmetry-adapted perturbation theory is used...
April 21, 2017: Journal of Chemical Physics
Priyadarsini Swain, Suneel K Srivastava, Sanjeev K Srivastava
Metallic Ni1-x V x alloys exhibit a ferromagnetic to paramagnetic disordered quantum phase transition in bulk. Such a phase transition is accompanied by a quantum Griffiths phase (QGP), featuring fractional power-law temperature dependences of physical variables, like magnetic susceptibility and specific heat, at low temperatures. As nanoparticles (NP's) usually exhibit properties significantly different from their bulk counterparts, it is intriguing to explore the occurrence of quantum Griffiths phase in Ni1-x V x nanoalloys...
April 21, 2017: Scientific Reports
Stefano Stassi, Alessandro Chiadò, Giuseppe Calafiore, Gianluca Palmara, Stefano Cabrini, Carlo Ricciardi
Fano resonance refers to an interference between localized and continuum states that was firstly reported for atomic physics and solid-state quantum devices. In recent years, Fano interference gained more and more attention for its importance in metamaterials, nanoscale photonic devices, plasmonic nanoclusters and surface-enhanced Raman scattering (SERS). Despite such interest in nano-optics, no experimental evidence of Fano interference was reported up to now for purely nanomechanical resonators, even if classical mechanical analogies were referred from a theoretical point of view...
April 21, 2017: Scientific Reports
Terry Farrelly, Fernando G S L Brandão, Marcus Cramer
Thermal states are the bedrock of statistical physics. Nevertheless, when and how they actually arise in closed quantum systems is not fully understood. We consider this question for systems with local Hamiltonians on finite quantum lattices. In a first step, we show that states with exponentially decaying correlations equilibrate after a quantum quench. Then, we show that the equilibrium state is locally equivalent to a thermal state, provided that the free energy of the equilibrium state is sufficiently small and the thermal state has exponentially decaying correlations...
April 7, 2017: Physical Review Letters
Bo Yang, Zi-Xiang Hu, Ching Hua Lee, Z Papić
We generalize the notion of Haldane pseudopotentials to anisotropic fractional quantum Hall (FQH) systems that are physically realized, e.g., in tilted magnetic field experiments or anisotropic band structures. This formalism allows us to expand any translation-invariant interaction over a complete basis, and directly reveals the intrinsic metric of incompressible FQH fluids. We show that purely anisotropic pseudopotentials give rise to new types of bound states for small particle clusters in the infinite plane, and can be used as a diagnostic of FQH nematic order...
April 7, 2017: Physical Review Letters
Cheng Wu, Bing Bai, Yang Liu, Xiaoming Zhang, Meng Yang, Yuan Cao, Jianfeng Wang, Shaohua Zhang, Hongyan Zhou, Xiheng Shi, Xiongfeng Ma, Ji-Gang Ren, Jun Zhang, Cheng-Zhi Peng, Jingyun Fan, Qiang Zhang, Jian-Wei Pan
Random numbers are indispensable for a variety of applications ranging from testing physics foundations to information encryption. In particular, nonlocality test provide strong evidence for our current understanding of nature-quantum mechanics. All the random number generators (RNGs) used for the existing tests are constructed locally, making the test results vulnerable to the freedom-of-choice loophole. We report an experimental realization of RNGs based on the arrival time of cosmic photons. The measurement outcomes (raw data) pass the standard NIST statistical test suite...
April 7, 2017: Physical Review Letters
Bo Fu, Wei Zhu, Qinwei Shi, Qunxiang Li, Jinlong Yang, Zhenyu Zhang
Exploiting the enabling power of the Lanczos method in momentum space, we determine accurately the quasiparticle and scaling properties of disordered three-dimensional Dirac semimetals surrounding the quantum critical point separating the semimetal and diffusive metal regimes. We unveil that the imaginary part of the quasiparticle self-energy obeys a common power law before, at, and after the quantum phase transition, but the power law is nonuniversal, whose exponent is dependent on the disorder strength. More intriguingly, whereas a common power law is also found for the real part of the self-energy before and after the phase transition, a distinctly different behavior is identified at the critical point, characterized by the existence of a nonanalytic logarithmic singularity...
April 7, 2017: Physical Review Letters
Leonardo Banchi, Joaquín Fernández-Rossier, Cyrus F Hirjibehedin, Sougato Bose
The development of communication channels at the ultimate size limit of atomic scale physical dimensions will make the use of quantum entities an imperative. In this regime, quantum fluctuations naturally become prominent and are generally considered to be detrimental. Here, we show that for spin-based information processing, these fluctuations can be uniquely exploited to gate the flow of classical binary information across a magnetic chain in thermal equilibrium. Moreover, this information flow can be controlled with a modest external magnetic field that drives the system through different many-body quantum phases in which the orientation of the final spin does or does not reflect the orientation of the initial input...
April 7, 2017: Physical Review Letters
Uwe Manthe
Multi-configurational time-dependent Hartree (MCTDH) based approaches are efficient, accurate, and versatile methods for high-dimensional quantum dynamics simulations. Applications range from detailed investigations of polyatomic reaction processes in the gas phase to high-dimensional simulations studying the dynamics of condensed phase systems described by typical solid state physics model Hamiltonians. The present article presents an overview of the different areas of application and provides on a comprehensive review of the underlying theory...
April 21, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Ichiro Yamato, Takeshi Murata, Andrei Khrennikov
We classify research fields in biology with respect to flows of materials, energy, and information. We investigate energy transducing mechanisms in biology, using as a representative the typical molecular rotary motor V1-ATPase from a bacterium Enterococcus hirae. The structures of several intermediates of the rotary motor are described and the molecular mechanism of the motor converting chemical energy into mechanical energy is discussed. Comments and considerations on the information flows in biology, especially on the thermodynamic entropy in quantum physical and biological systems, are presented in section 3 in a biologist friendly manner...
April 17, 2017: Progress in Biophysics and Molecular Biology
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