5,646 research outputs found
Fractional Quantum Hall Effect in Topological Flat Bands with Chern Number Two
Recent theoretical works have demonstrated various robust Abelian and
non-Abelian fractional topological phases in lattice models with topological
flat bands carrying Chern number C=1. Here we study hard-core bosons and
interacting fermions in a three-band triangular-lattice model with the lowest
topological flat band of Chern number C=2. We find convincing numerical
evidence of bosonic fractional quantum Hall effect at the filling
characterized by three-fold quasi-degeneracy of ground states on a torus, a
fractional Chern number for each ground state, a robust spectrum gap, and a gap
in quasihole excitation spectrum. We also observe numerical evidence of a
robust fermionic fractional quantum Hall effect for spinless fermions at the
filling with short-range interactions.Comment: 5 pages, 7 figures, with Supplementary Materia
Phases of the infinite U Hubbard model
We apply the density matrix renormalization group (DMRG) to study the phase
diagram of the infinite U Hubbard model on 2-, 4-, and 6-leg ladders. Where the
results are largely insensitive to the ladder width, we consider the results
representative of the 2D square lattice model. We find a fully polarized
ferromagnetic Fermi liquid phase when n, the density of electrons per site, is
in the range 1>n>n_F ~ 4/5. For n=3/4 we find an unexpected commensurate
insulating "checkerboard" phase with coexisting bond density order with 4 sites
per unit cell and block spin antiferromagnetic order with 8 sites per unit
cell. For 3/4 > n, the wider ladders have unpolarized groundstates, which is
suggestive that the same is true in 2D
Non-Abelian Quantum Hall Effect in Topological Flat Bands
Inspired by recent theoretical discovery of robust fractional topological
phases without a magnetic field, we search for the non-Abelian quantum Hall
effect (NA-QHE) in lattice models with topological flat bands (TFBs). Through
extensive numerical studies on the Haldane model with three-body hard-core
bosons loaded into a TFB, we find convincing numerical evidence of a stable
bosonic NA-QHE, with the characteristic three-fold quasi-degeneracy of
ground states on a torus, a quantized Chern number, and a robust spectrum gap.
Moreover, the spectrum for two-quasihole states also shows a finite energy gap,
with the number of states in the lower energy sector satisfying the same
counting rule as the Moore-Read Pfaffian state.Comment: 5 pages, 7 figure
Differentiable Quantum Architecture Search
Quantum architecture search (QAS) is the process of automating architecture
engineering of quantum circuits. It has been desired to construct a powerful
and general QAS platform which can significantly accelerate current efforts to
identify quantum advantages of error-prone and depth-limited quantum circuits
in the NISQ era. Hereby, we propose a general framework of differentiable
quantum architecture search (DQAS), which enables automated designs of quantum
circuits in an end-to-end differentiable fashion. We present several examples
of circuit design problems to demonstrate the power of DQAS. For instance,
unitary operations are decomposed into quantum gates, noisy circuits are
re-designed to improve accuracy, and circuit layouts for quantum approximation
optimization algorithm are automatically discovered and upgraded for
combinatorial optimization problems. These results not only manifest the vast
potential of DQAS being an essential tool for the NISQ application
developments, but also present an interesting research topic from the
theoretical perspective as it draws inspirations from the newly emerging
interdisciplinary paradigms of differentiable programming, probabilistic
programming, and quantum programming.Comment: 9.1 pages + Appendix, 5 figure
New Method for Numerically Solving the Chemical Potential Dependence of the Dressed Quark Propagator
Based on the rainbow approximation of Dyson-Schwinger equation and the
assumption that the inverse dressed quark propagator at finite chemical
potential is analytic in the neighborhood of , a new method for
obtaining the dressed quark propagator at finite chemical potential from
the one at zero chemical potential is developed. Using this method the dressed
quark propagator at finite chemical potential can be obtained directly from the
one at zero chemical potential without the necessity of numerically solving the
corresponding coupled integral equations by iteration methods. A comparison
with previous results is given.Comment: Revtex, 14 pages, 5 figure
Integration of Multispectral Face Recognition and Multi-PTZ Camera Automated Surveillance for Security Applications
Due to increasing security concerns, a complete security system should consist of two major components, a computer-based face-recognition system and a real-time automated video surveillance system. A computer-based face-recognition system can be used in gate access control for identity authentication. In recent studies, multispectral imaging and fusion of multispectral narrow-band images in the visible spectrum have been employed and proven to enhance the recognition performance over conventional broad-band images, especially when the illumination changes. Thus, we present an automated method that specifies the optimal spectral ranges under the given illumination. Experimental results verify the consistent performance of our algorithm via the observation that an identical set of spectral band images is selected under all tested conditions. Our discovery can be practically used for a new customized sensor design associated with given illuminations for an improved face recognition performance over conventional broad-band images. In addition, once a person is authorized to enter a restricted area, we still need to continuously monitor his/her activities for the sake of security. Because pantilt-zoom (PTZ) cameras are capable of covering a panoramic area and maintaining high resolution imagery for real-time behavior understanding, researches in automated surveillance systems with multiple PTZ cameras have become increasingly important. Most existing algorithms require the prior knowledge of intrinsic parameters of the PTZ camera to infer the relative positioning and orientation among multiple PTZ cameras. To overcome this limitation, we propose a novel mapping algorithm that derives the relative positioning and orientation between two PTZ cameras based on a unified polynomial model. This reduces the dependence on the knowledge of intrinsic parameters of PTZ camera and relative positions. Experimental results demonstrate that our proposed algorithm presents substantially reduced computational complexity and improved flexibility at the cost of slightly decreased pixel accuracy as compared to Chen and Wang\u27s method [18]. © Versita sp. z o.o
Anomalous acoustic plasmons in two-dimensional over-tilted Dirac bands
The over-tilting of type-II Dirac cones has led to various fascinating
quantum phenomena. Here we find two anomalous acoustic plasmons (AAPs) are
dictated by the distinct geometry of two-dimensional (2D) type-II Dirac cones,
far beyond the conventional \text{\ensuremath{\sqrt{q}}} plasmon. One AAP
originates from the strong hybridization of two pockets at one Dirac point,
whereas the other is attributed to the significant enhancement of the band
correlation around the open Fermi surface. Remarkably, the plasmons exhibit
valley-dependent chirality along the tilting direction due to the chiral
electron dispersion. Meanwhile, we discuss the tunability of plasmon dispersion
and lifetime by tuning the gap and dielectric substrate. Our work provides a
promising way to generate the novel plasmons in Dirac materials.Comment: 6 pages, 5 figure
The roles of edge-based and surface-based information in the dynamic neural representation of objects.
We combined multivariate pattern analysis (MVPA) and electroencephalogram (EEG) to investigate the role of edge, color, and other surface information in the neural representation of visual objects. Participants completed a one-back task in which they were presented with color photographs, grayscale images, and line drawings of animals, tools, and fruits. Our results provide the first neural evidence that line drawings elicit similar neural activities as color photographs and grayscale images during the 175-305 ms window after the stimulus onset. Furthermore, we found that other surface information, rather than color information, facilitates decoding accuracy in the early stages of object representations and affects the speed of this. These results provide new insights into the role of edge-based and surface-based information in the dynamic process of neural representations of visual objects
Hexa-μ2-benzoato-bis(2,2′-bipyridyl)trimanganese(II) monohydrate
The complex molecule of the title compound, [Mn3(C7H5O2)6(C10H8N2)2]·H2O, contains a linear array of divalent manganese ions. The central MnII atom, which is located on a crystallographic inversion center, is coordinated octahedrally by six benzoate O atoms. The two terminal MnII ions are six-coordinated by four benzoate O atoms and two N atoms of 2,2′-bipyridyl. The central MnII atom and the terminal MnII ions are bridged by four benzoate ligands in a bidentate fashion, whereas the other two carboxylate ligands form bridges through one O atom only and chelate the terminal MnII atom. The molecules pack together via van der Waals attractions and C—H⋯O hydrogen bonds
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