2,873 research outputs found
Exactly Solvable Points and Symmetry-Protected Topological Phases of Quantum Spins on a Zig-Zag Lattice
A large number of symmetry-protected topological (SPT) phases have been
hypothesized for strongly interacting spin-1/2 systems in one dimension.
Realizing these SPT phases, however, often demands fine-tunings hard to reach
experimentally. And the lack of analytical solutions hinders the understanding
of their many-body wave functions. Here we show that two kinds of SPT phases
naturally arise for ultracold polar molecules confined in a zigzag optical
lattice. This system, motivated by recent experiments, is described by a spin
model whose exchange couplings can be tuned by an external field to reach
parameter regions not studied before for spin chains or ladders. Within the
enlarged parameter space, we find the ground state wave function can be
obtained exactly along a line and at a special point, for these two phases
respectively. These exact solutions provide a clear physical picture for the
SPT phases and their edge excitations. We further obtain the phase diagram by
using infinite time-evolving block decimation, and discuss the phase
transitions between the two SPT phases and their experimental signatures.Comment: 5+7 pages, 3+5 figure
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A words-of-interest model of sketch representation for image retrieval
In this paper we propose a method for sketch-based image retrieval. Sketch is a magical medium which is capable of conveying semantic messages for user. It’s in accordance with user’s cognitive psychology to retrieve images with sketch. In order to narrow down the semantic gap between the user and the images in database, we preprocess all the images into sketches by the coherent line drawing algorithm. During the process of sketches extraction, saliency maps are used to filter out the redundant background information, while preserve the important semantic information. We use a variant of Words-of-Interest model to retrieve relevant images for the user according to the query. Words-of-Interest (WoI) model is based on Bag-ofvisual Words (BoW) model, which has been proven successfully for information retrieval. Bag-of-Words ignores the spatial relationships among visual words, which are important for sketch representation. Our method takes advantage of the spatial information of the query to select words of interest. Experimental results demonstrate that our sketch-based retrieval method achieves a good tradeoff between retrieval accuracy and semantic representation of users’ query
Analytic thermodynamics and thermometry of Gaudin-Yang Fermi gases
We study the thermodynamics of a one-dimensional attractive Fermi gas (the
Gaudin-Yang model) with spin imbalance. The exact solution has been known from
the thermodynamic Bethe ansatz for decades, but it involves an infinite number
of coupled nonlinear integral equations whose physics is difficult to extract.
Here the solution is analytically reduced to a simple, powerful set of four
algebraic equations. The simplified equations become universal and exact in the
experimental regime of strong interaction and relatively low temperature. Using
the new formulation, we discuss the qualitative features of finite-temperature
crossover and make quantitative predictions on the density profiles in traps.
We propose a practical two-stage scheme to achieve accurate thermometry for a
trapped spin-imbalanced Fermi gas.Comment: 4 pages, 2 figures; published version (v2
Noise suppression of on-chip mechanical resonators by chaotic coherent feedback
We propose a method to decouple the nanomechanical resonator in
optomechanical systems from the environmental noise by introducing a chaotic
coherent feedback loop. We find that the chaotic controller in the feedback
loop can modulate the dynamics of the controlled optomechanical system and
induce a broadband response of the mechanical mode. This broadband response of
the mechanical mode will cut off the coupling between the mechanical mode and
the environment and thus suppress the environmental noise of the mechanical
modes. As an application, we use the protected optomechanical system to act as
a quantum memory. It's shown that the noise-decoupled optomechanical quantum
memory is efficient for storing information transferred from coherent or
squeezed light
Total Nuclear Reaction Cross Section Induced by Halo Nuclei and Stable Nuclei
We develop the method for the calculation of the total reaction cross
sections induced by the halo nuclei and stable nuclei. This approach is based
on the Glauber theory, which is valid for nuclear reactions at high energy. It
is extended for nuclear reactions at low energy and intermediate energy by
including both the quantum correction and Coulomb correction under the
assumption of the effective nuclear density distribution. The calculated
results of the total reaction cross section induced by stable nuclei agree well
with the 30 experimental data within 10 percent accuracy.The comparison between
the numerical results and the 20 experimental data for the total nuclear
reaction cross section induced by the neutron halo nuclei and the proton halo
nuclei indicates a satisfactory agreement after considering the halo structure
of these nuclei, which implies the quite different mean fields for the nuclear
reactions induced by halo nuclei and stable nuclei. The halo nucleon
distributions and the root mean square radii of these nuclei can be extracted
from above comparison based on the improved Glauber model, which indicate
clearly the halo structures of these nuclei. Especially, it is clear to see
that the medium correction of the nucleon-nucleon collision has little effect
on the total reaction cross sections induced by the halo nuclei due to the very
weak binding and the very extended density distribution.Comment: 15 pages,2 figures. Communucations in Theoretical Physics, (2003) in
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