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Quantum physics

Sven Dirkmann, Mirko Hansen, Martin Ziegler, Hermann Kohlstedt, Thomas Mussenbrock
In this work we report on the role of ion transport for the dynamic behavior of a double barrier quantum mechanical Al/Al2O3/NbxOy/Au memristive device based on numerical simulations in conjunction with experimental measurements. The device consists of an ultra-thin NbxOy solid state electrolyte between an Al2O3 tunnel barrier and a semiconductor metal interface at an Au electrode. It is shown that the device provides a number of interesting features such as an intrinsic current compliance, a relatively long retention time, and no need for an initialization step...
October 20, 2016: Scientific Reports
C F Barenghi, Y A Sergeev, A W Baggaley
Experiments and numerical simulations of turbulent (4)He and (3)He-B have established that, at hydrodynamic length scales larger than the average distance between quantum vortices, the energy spectrum obeys the same 5/3 Kolmogorov law which is observed in the homogeneous isotropic turbulence of ordinary fluids. The importance of the 5/3 law is that it points to the existence of a Richardson energy cascade from large eddies to small eddies. However, there is also evidence of quantum turbulent regimes without Kolmogorov scaling...
October 20, 2016: Scientific Reports
Guanglei Wang, Ying-Cheng Lai, Celso Grebogi
Recently, the phenomenon of quantum-classical correspondence breakdown was uncovered in optomechanics, where in the classical regime the system exhibits chaos but in the corresponding quantum regime the motion is regular - there appears to be no signature of classical chaos whatsoever in the corresponding quantum system, generating a paradox. We find that transient chaos, besides being a physically meaningful phenomenon by itself, provides a resolution. Using the method of quantum state diffusion to simulate the system dynamics subject to continuous homodyne detection, we uncover transient chaos associated with quantum trajectories...
October 17, 2016: Scientific Reports
Małgorzata Białous, Vitalii Yunko, Szymon Bauch, Michał Ławniczak, Barbara Dietz, Leszek Sirko
We present experimental studies of the power spectrum and other fluctuation properties in the spectra of microwave networks simulating chaotic quantum graphs with violated time reversal invariance. On the basis of our data sets, we demonstrate that the power spectrum in combination with other long-range and also short-range spectral fluctuations provides a powerful tool for the identification of the symmetries and the determination of the fraction of missing levels. Such a procedure is indispensable for the evaluation of the fluctuation properties in the spectra of real physical systems like, e...
September 30, 2016: Physical Review Letters
E Shchukin, P van Loock
We present two results which combined enable one to reliably detect multimode, multipartite entanglement in the presence of measurement errors. The first result leads to a method to compute the best (approximated) physical covariance matrix given a measured nonphysical one assuming that no additional information about the measurement is available except the standard deviations from the mean values. The other result states that a widely used entanglement condition is a consequence of negativity of partial transposition...
September 30, 2016: Physical Review Letters
Eugene Stephane Mananga, Bingwen Hu
The importance of the average Hamiltonian theory and its antecedent the Magnus expansion are discussed. The investigation of its convergence in different situations is very important. In this paper, we introduced a well-established approach to minimize the zeroth order average Hamiltonian for modified composite pulse sequence in quadrupolar spectroscopy of spin-1. We designed two modified composite pulse sequences constructed by modifying the timing sequence in the original composite pulse sequences17. We tested various configurations of times associated with the free evolution of spin system in the modified composite pulses...
October 14, 2016: Journal of Physical Chemistry. A
O Coquand, D Mouhanna
We investigate the flat phase of quantum polymerized phantom membranes by means of a nonperturbative renormalization group approach. We first implement this formalism for general quantum polymerized membranes and derive the flow equations that encompass both quantum and thermal fluctuations. We then deduce and analyze the flow equations relevant to study the flat phase and discuss their salient features: quantum to classical crossover and, in each of these regimes, strong to weak coupling crossover. We finally illustrate these features in the context of free-standing graphene physics...
September 2016: Physical Review. E
Fernando Haas, Shahzad Mahmood
Nonlinear ion-acoustic waves are analyzed in a nonrelativistic magnetized quantum plasma with arbitrary degeneracy of electrons. Quantum statistics is taken into account by means of the equation of state for ideal fermions at arbitrary temperature. Quantum diffraction is described by a modified Bohm potential consistent with finite-temperature quantum kinetic theory in the long-wavelength limit. The dispersion relation of the obliquely propagating electrostatic waves in magnetized quantum plasma with arbitrary degeneracy of electrons is obtained...
September 2016: Physical Review. E
Tao Liu, Wei Li, Gang Su
Three different tensor network (TN) optimization algorithms are employed to accurately determine the ground state and thermodynamic properties of the spin-3/2 kagome Heisenberg antiferromagnet. We found that the sqrt[3]×sqrt[3] state (i.e., the state with 120^{∘} spin configuration within a unit cell containing 9 sites) is the ground state of this system, and such an ordered state is melted at any finite temperature, thereby clarifying the existing experimental controversies. Three magnetization plateaus (m/m_{s}=1/3,23/27, and 25/27) were obtained, where the 1/3-magnetization plateau has been observed experimentally...
September 2016: Physical Review. E
Lucas Kocia, Anna Klales
The time-dependent WKB approximation for a coherent state is expanded to third order around a guiding real trajectory, allowing for the novel treatment of nonlinearity in its semiclassical dynamics, which is generally present in all physical systems far from the classical regime. The result is a closed-form solution consisting of a linear combination of Airy functions and their derivatives multiplied by an exponential. The expression's ability to capture nonlinearity is demonstrated by examining the autocorrelation of initial coherent states in anharmonic systems with few to many contributing periodic orbits...
September 2016: Physical Review. E
Artur S L Malabarba, Terry Farrelly, Anthony J Short
By using a physically relevant and theory independent definition of measurement-based equilibration, we show quantitatively that equilibration is easier for quantum systems than for classical systems, in the situation where the initial state of the system is completely known (a pure state). This shows that quantum equilibration is a fundamental aspect of many quantum systems, while classical equilibration relies on experimental ignorance. When the state is not completely known (a mixed state), this framework also shows that quantum equilibration requires weaker conditions...
September 2016: Physical Review. E
Haohua Wen, C H Woo
The average energy needed to create a magnon is high in ferromagnetic metals due to the high-strength spin stiffness, which results in strong quantization effects that could be important even at thousands of degrees. To take into account quantum statistics at such high temperatures, the associated effects of anharmonicity of the spin vibrations must be taken into account. In addition to the complex nature of such effects, anharmonicity also affects the occupation of the density of state of the vibration states in the context of quantum statistics...
September 2016: Physical Review. E
Ryo Okamoto, Shigeki Takeuchi
The interference between two paths of a single photon at a double slit is widely considered to be the most paradoxical result of quantum theory. Here is a new interesting question to the phenomenon: can a single shutter simultaneously close two slits by effectively being in a superposition of different locations? Aharonov and Vaidman have shown that it is indeed possible to construct a quantum shutter that can close two slits and reflect a probe photon perfectly when its initial and final states are appropriately selected...
October 14, 2016: Scientific Reports
Naohiro Fujita, Daisuke Matsumoto, Yuki Sakurai, Kenji Kawahara, Hiroki Ago, Taishi Takenobu, Kazuhiro Marumoto
Graphene has been actively investigated as an electronic material owing to many excellent physical properties, such as high charge mobility and quantum Hall effect, due to the characteristics of a linear band structure and an ideal two-dimensional electron system. However, the correlations between the transport characteristics and the spin states of charge carriers or atomic vacancies in graphene have not yet been fully elucidated. Here, we show the spin states of single-layer graphene to clarify the correlations using electron spin resonance (ESR) spectroscopy as a function of accumulated charge density using transistor structures...
October 12, 2016: Scientific Reports
Jonny Proppe, Tamara Husch, Gregor N Simm, Markus Reiher
For the quantitative understanding of complex chemical reaction mechanisms, it is, in general, necessary to accurately determine the corresponding free energy surface and to solve the resulting continuous-time reaction rate equations for a continuous state space. For a general (complex) reaction network, it is computationally hard to fulfill these two requirements. However, it is possible to approximately address these challenges in a physically consistent way. On the one hand, it may be sufficient to consider approximate free energies if a reliable uncertainty measure can be provided...
October 12, 2016: Faraday Discussions
Michael Niklas, Mónica Benito, Sigmund Kohler, Gloria Platero
We analyze an AC-driven dimer chain connected to a strongly biased electron source and drain. It turns out that the resulting transport exhibits fingerprints of topology. They are particularly visible in the driving-induced current suppression and the Fano factor. Thus, shot noise measurements provide a topological phase diagram as a function of the driving parameters. The observed phenomena can be explained physically by a mapping to an effective time-independent Hamiltonian and the emergence of edge states...
November 11, 2016: Nanotechnology
V S Perunicic, C D Hill, L T Hall, L C L Hollenberg
Imaging the atomic structure of a single biomolecule is an important challenge in the physical biosciences. Whilst existing techniques all rely on averaging over large ensembles of molecules, the single-molecule realm remains unsolved. Here we present a protocol for 3D magnetic resonance imaging of a single molecule using a quantum spin probe acting simultaneously as the magnetic resonance sensor and source of magnetic field gradient. Signals corresponding to specific regions of the molecule's nuclear spin density are encoded on the quantum state of the probe, which is used to produce a 3D image of the molecular structure...
October 11, 2016: Nature Communications
Artur F Izmaylov, Jiaru Li, Loic Joubert-Doriol
Electronic wave-functions in the adiabatic representation acquire nontrivial geometric phases (GPs) when corresponding potential energy surfaces undergo conical intersection (CI). These GPs have profound effects on the nuclear quantum dynamics and cannot be eliminated in the adiabatic representation without changing the physics of the system. To define dynamical effects arising from the GP presence the nuclear quantum dynamics of the CI containing system is compared with that of the system with artificially removed GP...
October 10, 2016: Journal of Chemical Theory and Computation
Justyna Dominikowska, Mirosław Jabłoński, Marcin Palusiak
The Hellmann-Feynman theorem, when applied to nuclear coordinates in a molecular system, states that Feynman forces, i.e. forces acting on a nucleus in a molecule, are solely of an electrostatic nature. This theorem is described by Slater as "the most powerful" theorem applicable to molecules. However, its possibilities have hardly been harnessed. This work presents the use of the Hellmann-Feynman theorem in conjunction with the partitioning of the molecular space into atoms in the spirit of the quantum theory of atoms in molecules (QTAIM)...
September 14, 2016: Physical Chemistry Chemical Physics: PCCP
Haoliang Qian, Yuzhe Xiao, Zhaowei Liu
With the size of plasmonic devices entering into the nanoscale region, the impact of quantum physics needs to be considered. In the past, the quantum size effect on linear material properties has been studied extensively. However, the nonlinear aspects have not been explored much so far. On the other hand, much effort has been put into the field of integrated nonlinear optics and a medium with large nonlinearity is desirable. Here we study the optical nonlinear properties of a nanometre scale gold quantum well by using the z-scan method and nonlinear spectrum broadening technique...
October 10, 2016: Nature Communications
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