55,274 research outputs found
Effects of spontaneous symmetry break in the origin of non-analytic behavior of entanglement at quantum phase transitions
We present an example where Spontaneous Symmetry Breaking may effect not only
the behavior of the entanglement at Quantum Phase Transitions, but also the
origin of the non-analyticity. In particular, in the XXZ model, we study the
non analyticities in the concurrence between two spins, which was claimed to be
accidental, since it had its origin in the optimization involved in the
concurrence definition. We show that when one takes in account the effect of
the Spontaneous Symmetry Breaking, even tough the values of the entanglement
measure does not change, the origin the the non-analytical behavior changes: it
is not due to the optimization process anymore and in this sense it is a
"natural" non-analyticity. This is a much more subtle influence of the
Spontaneous Symmetry Breaking not noticed before. However the non-analytical
behavior still suggests a second order quantum phase transition and not the
first order that occurs and we explain why. We also show that the value of
entanglement between one site and the rest of the chain does change when taking
into account the Spontaneous Symmetry Breaking.Comment: a brief report, comments welcome. Text improved after referee
suggestion
Bell inequalities and entanglement at quantum phase transition in the XXZ Model
Entanglement and violation of Bell inequalities are aspects of quantum
nonlocality that have been often confused in the past. It is now known that
this equivalence is only true for pure states. Even though almost all the
studies of quantum correlations at quantum phase transitions deal only with
entanglement, we here argue that Bell inequalities can also reveal a general
quantum phase transition. This is also shown for a particular case of two
spin-1/2 particles in an infinite one-dimensional chain described by the XXZ
model. In this case, the Bell inequality is able to signal not only the
first-order phase transition, but also the infinite-order Kosterlitz-Thouless
quantum phase transition, which cannot be revealed either by the energy of the
system nor by the bipartite entanglement. We also show that although the
nearest-neighbor spins are entangled, they, unexpectedly, never violate the
Bell inequality. This indicates that the type of entanglement which is relevant
for quantum phase transition is not trivial, i.e., it cannot be revealed by the
Bell inequality.Comment: Published version. English improved and Sec. II shortened, after
referee suggestions. 7 pages, 6 figure
On the global convergent of an inexact quasi-Newton conditional gradient method for constrained nonlinear systems
In this paper, we propose a globally convergent method for solving
constrained nonlinear systems. The method combines an efficient Newton
conditional gradient method with a derivative-free and nonmonotone linesearch
strategy. The global convergence analysis of the proposed method is established
under suitable conditions, and some preliminary numerical experiments are given
to illustrate its performance
Convergence of the Gauss-Newton method for a special class of systems of equations under a majorant condition
In this paper, we study the Gauss-Newton method for a special class of
systems of nonlinear equation. Under the hypothesis that the derivative of the
function under consideration satisfies a majorant condition, semi-local
convergence analysis is presented. In this analysis the conditions and proof of
convergence are simplified by using a simple majorant condition to define
regions where the Gauss-Newton sequence is "well behaved". Moreover, special
cases of the general theory are presented as applications
A characterization of singular packing subspaces with an application to limit-periodic operators
A new characterization of the singular packing subspaces of general bounded
self-adjoint operators is presented, which is used to show that the set of
operators whose spectral measures have upper packing dimension equal to one is
a (in suitable metric spaces). As an application, it is proven that,
generically (in space of continuous sampling functions), spectral measures of
the limit-periodic Schr\"odinger operators have upper packing dimensions equal
to one. Consequently, in a generic set, these operators are quasiballistic.Comment: Accepted for publication in Forum Mathematicu
Asymptotic Quantum Search and a Quantum Algorithm for Calculation of a Lower Bound of the Probability of Finding a Diophantine Equation That Accepts Integer Solutions
Several mathematical problems can be modeled as a search in a database. An
example is the problem of finding the minimum of a function. Quantum algorithms
for solving this problem have been proposed and all of them use the quantum
search algorithm as a subroutine and several intermediate measurements are
realized. In this work, it is proposed a new quantum algorithm for finding the
minimum of a function in which quantum search is not used as a subroutine and
only one measurement is needed. This is also named asymptotic quantum search.
As an example, we propose a quantum algorithm based on asymptotic quantum
search and quantum counting able to calculate a lower bound of the probability
of finding a Diophantine equation with integer solution.Comment: Eleven pages, two figures. A complexity analysis is include
An Inexact Newton-like conditional gradient method for constrained nonlinear systems
In this paper, we propose an inexact Newton-like conditional gradient method
for solving constrained systems of nonlinear equations. The local convergence
of the new method as well as results on its rate are established by using a
general majorant condition. Two applications of such condition are provided:
one is for functions whose the derivative satisfies Holder-like condition and
the other is for functions that satisfies a Smale condition, which includes a
substantial class of analytic functions. Some preliminaries numerical
experiments illustrating the applicability of the proposed method for medium
and large problems are also presented
Performance Assessment of WhatsApp and IMO on Android Operating System (Lollipop and KitKat) during VoIP calls using 3G or WiFi
This paper assesses the performance of mobile messaging and VoIP connections.
We investigate the CPU usage of WhatsApp and IMO under different scenarios.
This analysis also enabled a comparison of the performance of these
applications on two Android operating system (OS) versions: KitKat or Lollipop.
Two models of smartphones were considered, viz. Galaxy Note 4 and Galaxy S4.
The applications behavior was statistically investigated for both sending and
receiving VoIP calls. Connections have been examined over 3G and WiFi. The
handset model plays a decisive role in CPU usage of the application. t-tests
showed that IMO has a better performance that WhatsApp whatever be the Android
at a significance level 1%, on Galaxy Note 4. In contrast, WhatsApp requires
less CPU than IMO on Galaxy S4 whatever be the OS and access (3G/WiFi). Galaxy
Note 4 using WiFi always outperformed S4 in terms of processing efficiency.Comment: 8 pages, Number of floats/tables/figures:
The Fourier-Like and Hartley-Like Wavelet Analysis Based on Hilbert Transforms
In continuous-time wavelet analysis, most wavelet present some kind of
symmetry. Based on the Fourier and Hartley transform kernels, a new wavelet
multiresolution analysis is proposed. This approach is based on a pair of
orthogonal wavelet functions and is named as the Fourier-Like and Hartley-Like
wavelet analysis. A Hilbert transform analysis on the wavelet theory is also
included.Comment: 7 pages, 10 figures, Anais do XXII Simp\'osio Brasileiro de
Telecomunica\c{c}\~oes, Campinas, 200
On the spectral Hausdorff dimension of 1D discrete Schr\"odinger operators under power decaying perturbations
We show that spectral Hausdorff dimensional properties of discrete
Schr\"oodinger operators with (1) Sturmian potentials of bounded density and
(2) a class of sparse potentials are preserved under suitable polynomial
decaying perturbations, when the spectrum of these perturbed operators have
some singular continuous component.Comment: To appear in Osaka Journal of Mathematic
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