13,018 research outputs found
Accurate determination of tensor network state of quantum lattice models in two dimensions
We have proposed a novel numerical method to calculate accurately the
physical quantities of the ground state with the tensor-network wave function
in two dimensions. We determine the tensor network wavefunction by a projection
approach which applies iteratively the Trotter-Suzuki decomposition of the
projection operator and the singular value decomposition of matrix. The norm of
the wavefunction and the expectation value of a physical observable are
evaluated by a coarse grain renormalization group approach. Our method allows a
tensor-network wavefunction with a high bond degree of freedom (such as D=8) to
be handled accurately and efficiently in the thermodynamic limit. For the
Heisenberg model on a honeycomb lattice, our results for the ground state
energy and the staggered magnetization agree well with those obtained by the
quantum Monte Carlo and other approaches.Comment: 4 pages 5 figures 2 table
Superfluid-Mott-Insulator Transition in a One-Dimensional Optical Lattice with Double-Well Potentials
We study the superfluid-Mott-insulator transition of ultracold bosonic atoms
in a one-dimensional optical lattice with a double-well confining trap using
the density-matrix renormalization group. At low density, the system behaves
similarly as two separated ones inside harmonic traps. At high density,
however, interesting features appear as the consequence of the quantum
tunneling between the two wells and the competition between the "superfluid"
and Mott regions. They are characterized by a rich step-plateau structure in
the visibility and the satellite peaks in the momentum distribution function as
a function of the on-site repulsion. These novel properties shed light on the
understanding of the phase coherence between two coupled condensates and the
off-diagonal correlations between the two wells.Comment: 5 pages, 7 figure
Optical properties of 4 A single-walled carbon nanotubes inside the zeolite channels studied from first principles calculations
The structural, electronic, and optical properties of 4 A single-walled
carbon nanotubes (SWNTs) contained inside the zeolite channels have been
studied based upon the density-functional theory in the local-density
approximation (LDA). Our calculated results indicate that the relaxed
geometrical structures for the smallest SWNTs in the zeolite channels are much
different from those of the ideal isolated SWNTs, producing a great effect on
their physical properties. It is found that all three kinds of 4 A SWNTs can
possibly exist inside the Zeolite channels. Especially, as an example, we have
also studied the coupling effect between the ALPO_4-5 zeolite and the tube
(5,0) inside it, and found that the zeolite has real effects on the electronic
structure and optical properties of the inside (5,0) tube.Comment: 9 pages, 6figure
Online Popularity and Topical Interests through the Lens of Instagram
Online socio-technical systems can be studied as proxy of the real world to
investigate human behavior and social interactions at scale. Here we focus on
Instagram, a media-sharing online platform whose popularity has been rising up
to gathering hundred millions users. Instagram exhibits a mixture of features
including social structure, social tagging and media sharing. The network of
social interactions among users models various dynamics including
follower/followee relations and users' communication by means of
posts/comments. Users can upload and tag media such as photos and pictures, and
they can "like" and comment each piece of information on the platform. In this
work we investigate three major aspects on our Instagram dataset: (i) the
structural characteristics of its network of heterogeneous interactions, to
unveil the emergence of self organization and topically-induced community
structure; (ii) the dynamics of content production and consumption, to
understand how global trends and popular users emerge; (iii) the behavior of
users labeling media with tags, to determine how they devote their attention
and to explore the variety of their topical interests. Our analysis provides
clues to understand human behavior dynamics on socio-technical systems,
specifically users and content popularity, the mechanisms of users'
interactions in online environments and how collective trends emerge from
individuals' topical interests.Comment: 11 pages, 11 figures, Proceedings of ACM Hypertext 201
Intense terahertz laser fields on a quantum dot with Rashba spin-orbit coupling
We investigate the effects of the intense terahertz laser field and the
spin-orbit coupling on single electron spin in a quantum dot. The laser field
and the spin-orbit coupling can strongly affect the electron density of states
and can excite a magnetic moment.
The direction of the magnetic moment depends on the symmetries of the system,
and its amplitude can be tuned by the strength and frequency of the laser field
as well as the spin-orbit coupling.Comment: 5 pages, 4 figures, to be published in J. Appl. Phy
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