9,043 research outputs found
Geometric phases in open systems: an exact model to study how they are corrected by decoherence
We calculate the geometric phase for an open system (spin-boson model) which
interacts with an environment (ohmic or nonohmic) at arbitrary temperature.
However there have been many assumptions about the time scale at which the
geometric phase can be measured, there has been no reported observation yet for
mixed states under nonunitary evolution. We study not only how they are
corrected by the presence of the different type of environments but also
estimate the corresponding times at which decoherence becomes effective. These
estimations should be taken into account when planning experimental setups to
study the geometric phase in the nonunitary regime, particularly important for
the application of fault-tolerant quantum computation.Comment: Revtex 4, 5 pages, one eps figure. Version Publishe
Effective photon mass and exact translating quantum relativistic structures
Using a variation of the celebrated Volkov solution, the Klein-Gordon
equation for a charged particle is reduced to a set of ordinary differential
equations, exactly solvable in specific cases. The new quantum relativistic
structures can reveal a localization in the radial direction perpendicular to
the wave packet propagation, thanks to a non-vanishing scalar potential. The
external electromagnetic field, the particle current density and the charge
density are determined. The stability analysis of the solutions is performed by
means of numerical simulations. The results are useful for the description of a
charged quantum test particle in the relativistic regime, provided spin effects
are not decisive
On Bargmann Representations of Wigner Function
By using the localized character of canonical coherent states, we give a
straightforward derivation of the Bargmann integral representation of Wigner
function (W). A non-integral representation is presented in terms of a
quadratic form V*FV, where F is a self-adjoint matrix whose entries are
tabulated functions and V is a vector depending in a simple recursive way on
the derivatives of the Bargmann function. Such a representation may be of use
in numerical computations. We discuss a relation involving the geometry of
Wigner function and the spacial uncertainty of the coherent state basis we use
to represent it.Comment: accepted for publication in J. Phys. A: Math. and Theo
Expanding Lie (super)algebras through abelian semigroups
We propose an outgrowth of the expansion method introduced by de Azcarraga et
al. [Nucl. Phys. B 662 (2003) 185]. The basic idea consists in considering the
direct product between an abelian semigroup S and a Lie algebra g. General
conditions under which relevant subalgebras can systematically be extracted
from S \times g are given. We show how, for a particular choice of semigroup S,
the known cases of expanded algebras can be reobtained, while new ones arise
from different choices. Concrete examples, including the M algebra and a
D'Auria-Fre-like Superalgebra, are considered. Finally, we find explicit,
non-trace invariant tensors for these S-expanded algebras, which are essential
ingredients in, e.g., the formulation of Supergravity theories in arbitrary
space-time dimensions.Comment: 42 pages, 8 figures. v2: Improved figures, updated notation and
terminolog
Selective and Efficient Quantum Process Tomography
In this paper we describe in detail and generalize a method for quantum
process tomography that was presented in [A. Bendersky, F. Pastawski, J. P.
Paz, Physical Review Letters 100, 190403 (2008)]. The method enables the
efficient estimation of any element of the --matrix of a quantum process.
Such elements are estimated as averages over experimental outcomes with a
precision that is fixed by the number of repetitions of the experiment.
Resources required to implement it scale polynomically with the number of
qubits of the system. The estimation of all diagonal elements of the
--matrix can be efficiently done without any ancillary qubits. In turn,
the estimation of all the off-diagonal elements requires an extra clean qubit.
The key ideas of the method, that is based on efficient estimation by random
sampling over a set of states forming a 2--design, are described in detail.
Efficient methods for preparing and detecting such states are explicitly shown.Comment: 9 pages, 5 figure
Minimal unitary representation of SU(2,2) and its deformations as massless conformal fields and their supersymmetric extensions
We study the minimal unitary representation (minrep) of SO(4,2) over an
Hilbert space of functions of three variables, obtained by quantizing its
quasiconformal action on a five dimensional space. The minrep of SO(4,2), which
coincides with the minrep of SU(2,2) similarly constructed, corresponds to a
massless conformal scalar in four spacetime dimensions. There exists a
one-parameter family of deformations of the minrep of SU(2,2). For positive
(negative) integer values of the deformation parameter \zeta one obtains
positive energy unitary irreducible representations corresponding to massless
conformal fields transforming in (0,\zeta/2) ((-\zeta/2,0)) representation of
the SL(2,C) subgroup. We construct the supersymmetric extensions of the minrep
of SU(2,2) and its deformations to those of SU(2,2|N). The minimal unitary
supermultiplet of SU(2,2|4), in the undeformed case, simply corresponds to the
massless N=4 Yang-Mills supermultiplet in four dimensions. For each given
non-zero integer value of \zeta, one obtains a unique supermultiplet of
massless conformal fields of higher spin. For SU(2,2|4) these supermultiplets
are simply the doubleton supermultiplets studied in arXiv:hep-th/9806042.Comment: Revised with an extended introduction and additional references.
Typos corrected. 49 pages; Latex fil
Charge inhomogeneities due to smooth ripples in graphene sheets
We study the effect of the curved ripples observed in the free standing
graphene samples on the electronic structure of the system. We model the
ripples as smooth curved bumps and compute the Green's function of the Dirac
fermions in the curved surface. Curved regions modify the Fermi velocity that
becomes a function of the point on the graphene surface and induce energy
dependent oscillations in the local density of states around the position of
the bump. The corrections are estimated to be of a few percent of the flat
density at the typical energies explored in local probes such as scanning
tunnel microscopy that should be able to observe the predicted correlation of
the morphology with the electronics. We discuss the connection of the present
work with the recent observation of charge anisotropy in graphene and propose
that it can be used as an experimental test of the curvature effects.Comment: 9 pages, 5 figures. v2: Abstract and discussion about experimental
consequences expande
Analgesic Activity of Ethanolic Extract of Voacanga Foetida (Bl.) K. Schum) on Male Mice
A study on the analgesic activity ethanolic extract of Voacanga foetida leaves has been conducted on male mice by using Writhing test. The mice were induced with 0.1 mL of glacial acetic acid 1%. The extract was administered orally in the doses of 250, 500, and 1000 mg/kg, suspended with NaCMC 1%, while 65 mg/kg acetosal was used as positive control. The data was analyzed with two way ANOVA. The study revealed that the extract exhibited analgesic effect insignificantly different with acetosal at the doses of 250, 500, and 1000 mg/kg. This effect was different with negative control (p<0.05)
Why the students of fifth year of the morning shift at Salomón de la Selva high school in Managua have a low level of proficiency in speaking and pronunciation skills in English as a foreign language
Nowadays English language has been one of the most relevant educational factors in Nicaragua and the population is being demanded to acquire it as a second language to exchange our cultural, social, political and economical aspects with foreign countries.
During many years students in high schools have been taking English as a part of the curriculum set by the minister of education and therefore used by the teachers in public schools.
In this research, we intend to find out the reasons that cause a low level of proficiency in speaking and pronunciation skills that students have in the second
language acquisition and mostly, we have observed that the students of fifth year at Salomón de la Selva high school have a lot of difficulties in speaking and pronunciation skills through the teaching and learning process in the classroom.
The problem has aroused our interest to look for specific information to help us find a solution.
We focus our attention on the possible factors that lead to the problem of our concern: the materials used in the classroom and the kind of techniques the teacher carries out in class in order to fulfill his objectives.
Our work lets you know about the previous knowledge and the linguistic problems the students have in English. And also how this can negatively affect them during their learning process in their last level of secondary schoo
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