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Quantum physics

Biao Yang, Qinghua Guo, Ben Tremain, Lauren E Barr, Wenlong Gao, Hongchao Liu, Benjamin Béri, Yuanjiang Xiang, Dianyuan Fan, Alastair P Hibbins, Shuang Zhang
The discovery of topological phases has introduced new perspectives and platforms for various interesting physics originally investigated in quantum contexts and then, on an equal footing, in classic wave systems. As a characteristic feature, nontrivial Fermi arcs, connecting between topologically distinct Fermi surfaces, play vital roles in the classification of Dirac and Weyl semimetals, and have been observed in quantum materials very recently. However, in classical systems, no direct experimental observation of Fermi arcs in momentum space has been reported so far...
July 21, 2017: Nature Communications
Louk Rademaker, Jan Zaanen
The ultimate consequence of quantum many-body physics is that even the air we breathe is governed by strictly unitary time evolution. The reason that we perceive it nonetheless as a completely classical high temperature gas is due to the incapacity of our measurement machines to keep track of the dense many-body entanglement of the gas molecules. The question thus arises whether there are instances where the quantum time evolution of a macroscopic system is qualitatively different from the equivalent classical system? Here we study this question through the expansion of noninteracting atomic clouds...
July 21, 2017: Scientific Reports
Reinier W Heeres, Philip Reinhold, Nissim Ofek, Luigi Frunzio, Liang Jiang, Michel H Devoret, Robert J Schoelkopf
A logical qubit is a two-dimensional subspace of a higher dimensional system, chosen such that it is possible to detect and correct the occurrence of certain errors. Manipulation of the encoded information generally requires arbitrary and precise control over the entire system. Whether based on multiple physical qubits or larger dimensional modes such as oscillators, the individual elements in realistic devices will always have residual interactions, which must be accounted for when designing logical operations...
July 21, 2017: Nature Communications
Ute Friederike Röhrig, Vincent Zoete, Olivier Michielin
Indoleamine 2,3-dioxygenase 1 (IDO1) is an important target in cancer immunotherapy. The most advanced clinical compound, epacadostat (INCB024360), binds to the heme cofactor of IDO1 through a N-hydroxyamidine function. Conflicting binding modes have recently been proposed, reporting iron binding either through the hydroxyamidine oxygen or nitrogen atoms. Here, we use quantum chemical calculations, docking, and QM/MM calculations based on available X-ray data to resolve this issue and to propose a physically meaningful binding mode...
July 21, 2017: Biochemistry
Mehdi Ansari-Rad, Juan Bisquert
Perovskite solar cells and fluorescent collectors formed by a dispersion of quantum dots in a transparent solid are paradigmatic devices for photon capture and utilization that involve the coupling of photon displacement, absorption and regeneration. In order to obtain information about the coupled photonic processes in systems involving photon recycling, we analyse the transfer function for modulated outgoing to incoming photon flux. We show the physical features of light-to-light impedance that reveals a trap-limited diffusion of photons coupled with the nonradiative recombination...
July 21, 2017: Journal of Physical Chemistry Letters
L Embon, Y Anahory, Ž L Jelić, E O Lachman, Y Myasoedov, M E Huber, G P Mikitik, A V Silhanek, M V Milošević, A Gurevich, E Zeldov
Quantized magnetic vortices driven by electric current determine key electromagnetic properties of superconductors. While the dynamic behavior of slow vortices has been thoroughly investigated, the physics of ultrafast vortices under strong currents remains largely unexplored. Here, we use a nanoscale scanning superconducting quantum interference device to image vortices penetrating into a superconducting Pb film at rates of tens of GHz and moving with velocities of up to tens of km/s, which are not only much larger than the speed of sound but also exceed the pair-breaking speed limit of superconducting condensate...
July 20, 2017: Nature Communications
Johannes Gooth, Anna C Niemann, Tobias Meng, Adolfo G Grushin, Karl Landsteiner, Bernd Gotsmann, Fabian Menges, Marcus Schmidt, Chandra Shekhar, Vicky Süß, Ruben Hühne, Bernd Rellinghaus, Claudia Felser, Binghai Yan, Kornelius Nielsch
The conservation laws, such as those of charge, energy and momentum, have a central role in physics. In some special cases, classical conservation laws are broken at the quantum level by quantum fluctuations, in which case the theory is said to have quantum anomalies. One of the most prominent examples is the chiral anomaly, which involves massless chiral fermions. These particles have their spin, or internal angular momentum, aligned either parallel or antiparallel with their linear momentum, labelled as left and right chirality, respectively...
July 19, 2017: Nature
Andreas Franz Resch, Hermann Fuchs, Dietmar Georg
Oxygen (<sup>16</sup>O) ions are a potential alternative to carbon ions in ion beam therapy. Their enhanced linear energy transfer indicates a higher relative biological effectiveness and a reduced oxygen enhancement ratio. Due to the limited availability of <sup>16</sup>O ion beams, Monte Carlo (MC) transport codes are important research tools to investigate their potential. The purpose of this study was to validate GATE/Geant4 for <sup>16</sup>O ion beam therapy on experimental data from literature...
July 18, 2017: Physics in Medicine and Biology
Robert L Z Hoye, Lana C Lee, Rachel C Kurchin, Tahmida N Huq, Kelvin H L Zhang, Melany Sponseller, Lea Nienhaus, Riley E Brandt, Joel Jean, James Alexander Polizzotti, Ahmed Kursumović, Moungi G Bawendi, Vladimir Bulović, Vladan Stevanović, Tonio Buonassisi, Judith L MacManus-Driscoll
Bismuth-based compounds have recently gained increasing attention as potentially nontoxic and defect-tolerant solar absorbers. However, many of the new materials recently investigated show limited photovoltaic performance. Herein, one such compound is explored in detail through theory and experiment: bismuth oxyiodide (BiOI). BiOI thin films are grown by chemical vapor transport and found to maintain the same tetragonal phase in ambient air for at least 197 d. The computations suggest BiOI to be tolerant to antisite and vacancy defects...
July 17, 2017: Advanced Materials
Ekin D Cubuk, Brad D Malone, Berk Onat, Amos Waterland, Efthimios Kaxiras
Many structural and mechanical properties of crystals, glasses, and biological macromolecules can be modeled from the local interactions between atoms. These interactions ultimately derive from the quantum nature of electrons, which can be prohibitively expensive to simulate. Machine learning has the potential to revolutionize materials modeling due to its ability to efficiently approximate complex functions. For example, neural networks can be trained to reproduce results of density functional theory calculations at a much lower cost...
July 14, 2017: Journal of Chemical Physics
Mariachiara Pastore, Xavier Assfeld, Edoardo Mosconi, Antonio Monari, Thibaud Etienne
We report a theoretical study on the analysis of the relaxed one-particle difference density matrix characterizing the passage from the ground to the excited state of a molecular system, as obtained from time-dependent density functional theory. In particular, this work aims at using the physics contained in the so-called Z-vector, which differentiates between unrelaxed and relaxed difference density matrices to analyze excited states' nature. For this purpose, we introduce novel quantum-mechanical quantities, based on the detachment/attachment methodology, for analysing the Z-vector transformation for different molecules and density functional theory functionals...
July 14, 2017: Journal of Chemical Physics
W S Dias, D Bertrand, M L Lyra
Recent experimental progress on the realization of quantum systems with highly controllable long-range interactions has impelled the study of quantum phase transitions in low-dimensional systems with power-law couplings. Long-range couplings mimic higher-dimensional effects in several physical contexts. Here, we provide the exact relation between the spectral dimension d at the band bottom and the exponent α that tunes the range of power-law hoppings of a one-dimensional ideal lattice Bose gas. We also develop a finite-size scaling analysis to obtain some relevant critical exponents and the critical temperature of the BEC transition...
June 2017: Physical Review. E
A Apostolakis, M K Awodele, K N Alekseev, F V Kusmartsev, A G Balanov
A quantum particle transport induced in a spatially periodic potential by a propagating plane wave has a number of important implications in a range of topical physical systems. Examples include acoustically driven semiconductor superlattices and cold atoms in an optical crystal. Here we apply a kinetic description of the directed transport in a superlattice beyond standard linear approximation, and utilize exact path-integral solutions of the semiclassical transport equation. We show that the particle drift and average velocities have nonmonotonic dependence on the wave amplitude with several prominent extrema...
June 2017: Physical Review. E
Zhan Zheng, Hailong Wang, Bing Cheng, Jietai Jing
We investigate different kinds of entanglement in a four-wave mixing process with a degenerate pump. After analyses on means and quantum fluctuations of the three output beams (Stokes, anti-Stokes, and pump), we verify the existence of genuine tripartite entanglement, and quantify bipartite, two-mode, as well as tripartite entanglement with the covariance matrix. We find out that the input pump power and the nonlinear coupling strength are the physical origins to enhance entanglement at a given photon loss.
July 15, 2017: Optics Letters
A Smith, J Knolle, D L Kovrizhin, R Moessner
The venerable phenomena of Anderson localization, along with the much more recent many-body localization, both depend crucially on the presence of disorder. The latter enters either in the form of quenched disorder in the parameters of the Hamiltonian, or through a special choice of a disordered initial state. Here, we present a model with localization arising in a very simple, completely translationally invariant quantum model, with only local interactions between spins and fermions. By identifying an extensive set of conserved quantities, we show that the system generates purely dynamically its own disorder, which gives rise to localization of fermionic degrees of freedom...
June 30, 2017: Physical Review Letters
K A Gilmore, J G Bohnet, B C Sawyer, J W Britton, J J Bollinger
We present a technique to measure the amplitude of a center-of-mass (c.m.) motion of a two-dimensional ion crystal of ∼100 ions. By sensing motion at frequencies far from the c.m. resonance frequency, we experimentally determine the technique's measurement imprecision. We resolve amplitudes as small as 50 pm, 40 times smaller than the c.m. mode zero-point fluctuations. The technique employs a spin-dependent, optical-dipole force to couple the mechanical oscillation to the electron spins of the trapped ions, enabling a measurement of one quadrature of the c...
June 30, 2017: Physical Review Letters
S A Selesnick, J P Rawling, Gualtiero Piccinini
Recently there has been much interest in the possible quantum-like behavior of the human brain in such functions as cognition, the mental lexicon, memory, etc., producing a vast literature. These studies are both empirical and theoretical, the tenets of the theory in question being mainly, and apparently inevitably, those of quantum physics itself, for lack of other arenas in which quantum-like properties are presumed to obtain. However, attempts to explain this behavior on the basis of actual quantum physics going on at the atomic or molecular level within some element of brain or neuronal anatomy (other than the ordinary quantum physics that underlies everything), do not seem to survive much scrutiny...
July 13, 2017: Journal of Biological Physics
R Krishna Kumar, X Chen, G H Auton, A Mishchenko, D A Bandurin, S V Morozov, Y Cao, E Khestanova, M Ben Shalom, A V Kretinin, K S Novoselov, L Eaves, I V Grigorieva, L A Ponomarenko, V I Fal'ko, A K Geim
Cyclotron motion of charge carriers in metals and semiconductors leads to Landau quantization and magneto-oscillatory behavior in their properties. Cryogenic temperatures are usually required to observe these oscillations. We show that graphene superlattices support a different type of quantum oscillation that does not rely on Landau quantization. The oscillations are extremely robust and persist well above room temperature in magnetic fields of only a few tesla. We attribute this phenomenon to repetitive changes in the electronic structure of superlattices such that charge carriers experience effectively no magnetic field at simple fractions of the flux quantum per superlattice unit cell...
July 14, 2017: Science
Ravi K Misra, Bat-El Cohen, Lior Iagher, Lioz Etgar
Three-dimensional (3D) perovskite has attracted a lot of attention due to its success in photovoltaic (PV) solar cells. However, one the major crucial issues lies in its stability, which has limited its commercialization. An important property of organic-inorganic perovskite is the possibility of forming a layered material using long organic cations that do not fit into the octahedral cage. The long organic cation acts as a "barrier" that "caps" the 3D perovskite forming the layered material. Controlling the number of perovskite layers could provide a confined structure with different chemical and physical properties than 3D perovskite has...
July 13, 2017: ChemSusChem
Wei Sun, Ya-Xi Huang, Yuanming Pan, Jin-Xiao Mi
Herbertsmithite- and kapellasite-type compounds with triangular lattices (i.e. Kagomé) as the most promising candidates for realizing the exotic quantum spin liquid (QSL) state have recently attracted significant attention in condensed matter physics and materials science but are often adversely affected by dimensional imperfections arising from significant cation mixing. Also, interaction mechanisms between the Kagomé lattices and ionic impurities remain unclear. Herein we report on the synthesis, crystal structures and magnetic properties of a new class of kapellasite-type compounds LnCu3(OH)6Cl3 (Ln = Nd and Sm) with two overlapped triangular lattices...
July 12, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
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