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Quantum physics

Steve Campbell, Sebastian Deffner
Achieving effectively adiabatic dynamics is a ubiquitous goal in almost all areas of quantum physics. Here, we study the speed with which a quantum system can be driven when employing transitionless quantum driving. As a main result, we establish a rigorous link between this speed, the quantum speed limit, and the (energetic) cost of implementing such a shortcut to adiabaticity. Interestingly, this link elucidates a trade-off between speed and cost, namely, that instantaneous manipulation is impossible as it requires an infinite cost...
March 10, 2017: Physical Review Letters
Kejing Ran, Jinghui Wang, Wei Wang, Zhao-Yang Dong, Xiao Ren, Song Bao, Shichao Li, Zhen Ma, Yuan Gan, Youtian Zhang, J T Park, Guochu Deng, S Danilkin, Shun-Li Yu, Jian-Xin Li, Jinsheng Wen
Kitaev interactions underlying a quantum spin liquid have long been sought, but experimental data from which their strengths can be determined directly, are still lacking. Here, by carrying out inelastic neutron scattering measurements on high-quality single crystals of α-RuCl_{3}, we observe spin-wave spectra with a gap of ∼2  meV around the M point of the two-dimensional Brillouin zone. We derive an effective-spin model in the strong-coupling limit based on energy bands obtained from first-principles calculations, and find that the anisotropic Kitaev interaction K term and the isotropic antiferromagnetic off-diagonal exchange interaction Γ term are significantly larger than the Heisenberg exchange coupling J term...
March 10, 2017: Physical Review Letters
C N Harvey, A Gonoskov, A Ilderton, M Marklund
Accelerated charges radiate, and therefore must lose energy. The impact of this energy loss on particle motion, called radiation reaction, becomes significant in intense-laser matter interactions, where it can reduce collision energies, hinder particle acceleration schemes, and is seemingly unavoidable. Here we show that this common belief breaks down in short laser pulses, and that energy losses and radiation reaction can be controlled and effectively switched off by appropriate tuning of the pulse length...
March 10, 2017: Physical Review Letters
N Xu, G Autès, C E Matt, B Q Lv, M Y Yao, F Bisti, V N Strocov, D Gawryluk, E Pomjakushina, K Conder, N C Plumb, M Radovic, T Qian, O V Yazyev, J Mesot, H Ding, M Shi
The Weyl semimetal phase is a recently discovered topological quantum state of matter characterized by the presence of topologically protected degeneracies near the Fermi level. These degeneracies are the source of exotic phenomena, including the realization of chiral Weyl fermions as quasiparticles in the bulk and the formation of Fermi arc states on the surfaces. Here, we demonstrate that these two key signatures show distinct evolutions with the bulk band topology by performing angle-resolved photoemission spectroscopy, supported by first-principles calculations, on transition-metal monophosphides...
March 10, 2017: Physical Review Letters
Christian Balz, Bella Lake, Manfred Reehuis, A T M Islam, Oleksandr Prokhnenko, Yogesh Singh, Philip Pattison, Sandor Toth
A detailed diffraction study of Ca<sub>10</sub>Cr<sub>7</sub>O<sub>28</sub> is presented which adds significant new insights into the structural and magnetic properties of this compound. A new crystal structure type was used where the a and b axes are doubled compared to previous models providing a more plausible structure where all crystallographic sites are fully occupied. The presence of two different valences of chromium was verified and the locations of the magnetic Cr<sup>5+</sup> and non-magnetic Cr<sup>6+</sup> ions were identified...
March 24, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Ngoc Han Tu, Yoichi Tanabe, Yosuke Satake, Khuong Kim Huynh, Le Huu Phuoc, Stephane Yu Matsushita, Katsumi Tanigaki
Uniform and large-area synthesis of bulk insulating ultrathin films is an important subject toward applications of a surface of three dimensional topological insulators (3D-TIs) in various electronic devices. We report epitaxial growth of bulk insulating 3D-TI Bi2-xSbxTe3-ySey (BSTS) ultrathin films, ranging from a few quintuple to several hundreds of layers, on mica in a large-area (1 cm(2)) via catalyst-free physical vapor deposition. These films can nondestructively be exfoliated using deionized water and transferred to various kinds of substrates as desired...
March 24, 2017: Nano Letters
Danuta Rusinska-Roszak
Intramolecular hydrogen bonding (HB) is one of the most studied noncovalent interactions of molecules. Many physical, spectral, and topological properties of compounds are under the influence of HB, and there are many parameters used to notice and to describe these changes. Hitherto, no general method of measurement of the energy of intramolecular hydrogen bond (EHB) has been put into effect. We propose the molecular tailoring approach (MTA) for EHB calculation, modified to apply it to Ar-O-H∙∙∙O=C systems...
March 18, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Stefania Sciara, Rosario Lo Franco, Giuseppe Compagno
Schmidt decomposition is a widely employed tool of quantum theory which plays a key role for distinguishable particles in scenarios such as entanglement characterization, theory of measurement and state purification. Yet, its formulation for identical particles remains controversial, jeopardizing its application to analyze general many-body quantum systems. Here we prove, using a newly developed approach, a universal Schmidt decomposition which allows faithful quantification of the physical entanglement due to the identity of particles...
March 23, 2017: Scientific Reports
Giorgio Colangelo, Ferran Martin Ciurana, Lorena C Bianchet, Robert J Sewell, Morgan W Mitchell
Measurement of spin precession is central to extreme sensing in physics, geophysics, chemistry, nanotechnology and neuroscience, and underlies magnetic resonance spectroscopy. Because there is no spin-angle operator, any measurement of spin precession is necessarily indirect, for example, it may be inferred from spin projectors at different times. Such projectors do not commute, and so quantum measurement back-action-the random change in a quantum state due to measurement-necessarily enters the spin measurement record, introducing errors and limiting sensitivity...
March 22, 2017: Nature
E N Bodunov, Yu A Antonov, A L Simões Gamboa
The non-exponential room temperature luminescence decay of colloidal quantum dots is often well described by a stretched exponential function. However, the physical meaning of the parameters of the function is not clear in the majority of cases reported in the literature. In this work, the room temperature stretched exponential luminescence decay of colloidal quantum dots is investigated theoretically in an attempt to identify the underlying physical mechanisms associated with the parameters of the function...
March 21, 2017: Journal of Chemical Physics
K Chang, A Eichler, J Rhensius, L Lorenzelli, C L Degen
Charge transport in nanostructures and thin films is fundamental to many phenomena and processes in science and technology, ranging from quantum effects and electronic correlations in mesoscopic physics, to integrated charge- or spin-based electronic circuits, to photoactive layers in energy research. Direct visualization of the charge flow in such structures is challenging due to their nanometer size and the itinerant nature of currents. In this work, we demonstrate noninvasive magnetic imaging of current density in two-dimensional conductor networks including metallic nanowires and carbon nanotubes...
March 24, 2017: Nano Letters
Xiangkai Kong, Qiangchun Liu, Changlin Zhang, Zhenmeng Peng, Qianwang Chen
The great success of graphene has encouraged the fast development of other two-dimensional (2D) nanosheets, which have attracted extensive attention in different scientific fields encompassing field effect transistors, lithium-ion batteries, and catalysis. With atomic-scale thickness, almost all of the atoms are exposed on the surface, providing an extremely high specific surface area, in conjunction with special physical, chemical, and electronic properties, owing to the quantum confinement effects, which enable their surface phase to be as important as the bulk counterparts...
March 22, 2017: Chemical Society Reviews
Carlos A Melo-Luna, Cristian E Susa, Andrés F Ducuara, Astrid Barreiro, John H Reina
Game theory is a well established branch of mathematics whose formalism has a vast range of applications from the social sciences, biology, to economics. Motivated by quantum information science, there has been a leap in the formulation of novel game strategies that lead to new (quantum Nash) equilibrium points whereby players in some classical games are always outperformed if sharing and processing joint information ruled by the laws of quantum physics is allowed. We show that, for a bipartite non zero-sum game, input local quantum correlations, and separable states in particular, suffice to achieve an advantage over any strategy that uses classical resources, thus dispensing with quantum nonlocality, entanglement, or even discord between the players' input states...
March 22, 2017: Scientific Reports
Norbert M Linke, Dmitri Maslov, Martin Roetteler, Shantanu Debnath, Caroline Figgatt, Kevin A Landsman, Kenneth Wright, Christopher Monroe
We run a selection of algorithms on two state-of-the-art 5-qubit quantum computers that are based on different technology platforms. One is a publicly accessible superconducting transmon device (www. RESEARCH: with limited connectivity, and the other is a fully connected trapped-ion system. Even though the two systems have different native quantum interactions, both can be programed in a way that is blind to the underlying hardware, thus allowing a comparison of identical quantum algorithms between different physical systems...
March 21, 2017: Proceedings of the National Academy of Sciences of the United States of America
Francis Beauvais
In previous articles, a description of 'unconventional' experiments (e.g. in vitro or clinical studies based on high dilutions, 'memory of water' or homeopathy) using quantum-like probability was proposed. Because the mathematical formulations of quantum logic are frequently an obstacle for physicians and biologists, a modified modeling that rests on classical probability is described in the present article. This modeling is inspired from a relational interpretation of quantum physics that applies not only to microscopic objects, but also to macroscopic structures, including experimental devices and observers...
February 2017: Homeopathy: the Journal of the Faculty of Homeopathy
Yue Lu, Yiliang Lin, Zhaowei Chen, Quanyin Hu, Yang Liu, Shuangjiang Yu, Wei Gao, Michael D Dickey, Zhen Gu
Effective endosomal escape remains as the "holy grail" for endocytosis-based intracellular drug delivery. To date, most of the endosomal escape strategies rely on small molecules, cationic polymers, or pore-forming proteins, which are often limited by the systemic toxicity and lack of specificity. We describe here a light-fueled liquid-metal transformer for effective endosomal escape-facilitated cargo delivery via a chemical-mechanical process. The nanoscale transformer can be prepared by a simple approach of sonicating a low-toxicity liquid-metal...
March 22, 2017: Nano Letters
Ludong Li, Leilei Gu, Zheng Lou, Zhiyong Fan, Guozhen Shen
Here we report fabrication of high-performance ultraviolet photodetectors based on a unique heterojunction device structure in which ZnO quantum dots were used to decorate Zn2SnO4 nanowires. Systematic investigations have shown their ultrahigh light-to-dark current ratio (up to 6.8 × 104), specific detectivity (up to 9.0×1017 Jones), photoconductive gain (up to 1.1 × 107), fast response, and excellent stability. Compared with a pristine Zn2SnO4 nanowire, a quantum dots decorated nanowire demonstrated about 10 times higher photocurrent and responsivity...
March 21, 2017: ACS Nano
Siying Che, Rina Dao, Weidong Zhang, Xiaoyu Lv, Haoran Li, Congmin Wang
A novel anion-functionalized fluorescent ionic liquid was designed and prepared, which was capable of capturing sulphur dioxide with high capacity and could also be used as a good colorimetric and fluorescent SO2 sensor. Compared to conventional fluorescent sensors, this fluorescent ionic liquid did not undergo aggregation-caused quenching or aggregation-induced emission, and the fluorescence was quenched when exposed to SO2, and the fluorescence would quench when exposed to SO2. The experimental absorption, spectroscopic investigation, and quantum chemical calculations indicated that the quenching of the fluorescence originated from SO2 physical absorption, not chemical absorption...
March 20, 2017: Chemical Communications: Chem Comm
Zhibin Yang, Wenjing Jie, Chun-Hin Mak, Shenghuang Lin, Huihong Lin, Xianfeng Yang, Feng Yan, Shu Ping Lau, Jianhua Hao
Large-scale synthesis of two-dimensional (2D) materials is one of the significant issues for fabricating layered materials into practical devices. As one of the typical III-VI semiconductors, InSe has attracted much attention due to its outstanding electrical transport property, attractive quantum physics characteristics and dramatic photoresponse when it is reduced to atomic scale. However, scalable synthesis of single phase 2D InSe has not yet been achieved so far, greatly hindering further fundamental studies and device applications...
March 19, 2017: ACS Nano
Panpan Zhou, Yu Xie, Jing Fang, Yun Ling, Changling Yu, Xiaoming Liu, Yuhua Dai, Yuancheng Qin, Dan Zhou
In this paper, the mesoporous TiO2 with different concentration of CdS quantum dots (i.e., x% CdS/TiO2) was successfully fabricated by the sol-gel method. The composition, structure and morphology of the nanocomposites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-vis diffuse reflectance spectroscopy (UV-Vis/DRS) and nitrogen physical adsorption test and so on. The proportion of CdS and TiO2 is very important for the photocatalytic performance...
March 8, 2017: Chemosphere
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