334 research outputs found
Dynamics of entanglement in a two-dimensional spin system
We consider the time evolution of entanglement in a finite two dimensional
transverse Ising model. The model consists of a set of 7 localized spin-1/2
particles in a two dimensional triangular lattice coupled through nearest
neighbor exchange interaction in presence of an external time dependent
magnetic field. The magnetic field is applied in different function forms:
step, exponential, hyperbolic and periodic. We found that the time evolution of
the entanglement shows an ergodic behavior under the effect of the time
dependent magnetic fields. Also we found that while the step magnetic field
causes great disturbance to the system creating rabid oscillations, the system
shows great controllability under the effect of the other magnetic fields where
the entanglement profile follows closely the shape of the applied field even
with the same frequency for periodic fields. This follow up trend breaks down
as the strength of the field, the transition constant for exponential and
hyperbolic, or frequency for periodic field increase leading to rapid
oscillations. We observed that the entanglement is very sensitive to the
initial value of the applied periodic field, the smaller the initial value the
less distorted is the entanglement profile. Furthermore, the effect of thermal
fluctuations is very devastating to the entanglement which decays very rapidly
as the temperature increases. Interestingly, although large value of the
magnetic field strength may yield small entanglement, it was found to be more
persistent against thermal fluctuations than the small field strengths
Scaling of entanglement at quantum phase transition for two-dimensional array of quantum dots
With Hubbard model, the entanglement scaling behavior in a two-dimensional
itinerant system is investigated. It has been found that, on the two sides of
the critical point denoting an inherent quantum phase transition (QPT), the
entanglement follows different scalings with the size just as an order
parameter does. This fact reveals the subtle role played by the entanglement in
QPT as a fungible physical resource
Entanglement Switch for Dipole Arrays
We propose a new entanglement switch of qubits consisting of electric
dipoles, oriented along or against an external electric field and coupled by
the electric dipole-dipole interaction. The pairwise entanglement can be tuned
and controlled by the ratio of the Rabi frequency and the dipole-dipole
coupling strength. Tuning the entanglement can be achieved for one, two and
three-dimensional arrangements of the qubits. The feasibility of building such
an entanglement switch is also discussed.Comment: 6 pages and 4 figures. To be published on Journal of Chemical Physic
Shooting Neural Networks Algorithm for Solving Boundary Value Problems in ODEs
The objective of this paper is to use Neural Networks for solving boundary value problems (BVPs) in Ordinary Differential Equations (ODEs). The Neural networks use the principle of Back propagation. Five examples are considered to show effectiveness of using the shooting techniques and neural network for solving the BVPs in ODEs. The convergence properties of the technique, which depend on the convergence of the integration technique and accuracy of the interpolation technique are considered
Simulated Quantum Computation of Global Minima
Finding the optimal solution to a complex optimization problem is of great
importance in practically all fields of science, technology, technical design
and econometrics. We demonstrate that a modified Grover's quantum algorithm can
be applied to real problems of finding a global minimum using modest numbers of
quantum bits. Calculations of the global minimum of simple test functions and
Lennard-Jones clusters have been carried out on a quantum computer simulator
using a modified Grover's algorithm. The number of function evaluations
reduced from O(N) in classical simulation to in quantum
simulation. We also show how the Grover's quantum algorithm can be combined
with the classical Pivot method for global optimization to treat larger
systems.Comment: 6 figures. Molecular Physics, in pres
Universal Programmable Quantum Circuit Schemes to Emulate an Operator
Unlike fixed designs, programmable circuit designs support an infinite number
of operators. The functionality of a programmable circuit can be altered by
simply changing the angle values of the rotation gates in the circuit. Here, we
present a new quantum circuit design technique resulting in two general
programmable circuit schemes. The circuit schemes can be used to simulate any
given operator by setting the angle values in the circuit. This provides a
fixed circuit design whose angles are determined from the elements of the given
matrix-which can be non-unitary-in an efficient way. We also give both the
classical and quantum complexity analysis for these circuits and show that the
circuits require a few classical computations. They have almost the same
quantum complexities as non-general circuits. Since the presented circuit
designs are independent from the matrix decomposition techniques and the global
optimization processes used to find quantum circuits for a given operator, high
accuracy simulations can be done for the unitary propagators of molecular
Hamiltonians on quantum computers. As an example, we show how to build the
circuit design for the hydrogen molecule.Comment: combined with former arXiv:1207.174
Speech Enhancement via EMD
WOSInternational audienceIn this study, two new approaches for speech signal noise reduction based on the empirical mode decomposition (EMD) recently introduced by Huang et al. (1998) are proposed. Based on the EMD, both reduction schemes are fully data-driven approaches. Noisy signal is decomposed adaptively into oscillatory components called intrinsic mode functions (IMFs), using a temporal decomposition called sifting process. Two strategies for noise reduction are proposed: filtering and thresholding. The basic principle of these two methods is the signal reconstruction with IMFs previously filtered, using the minimum mean-squared error (MMSE) filter introduced by I. Y. Soon et al. (1998), or thresholded using a shrinkage function. The performance of these methods is analyzed and compared with those of the MMSE filter and wavelet shrinkage. The study is limited to signals corrupted by additive white Gaussian noise. The obtained results show that the proposed denoising schemes perform better than the MMSE filter and wavelet approach
Experimental Evidence of Chaotic Resonance in Semiconductor Laser
تم في هذا البحث تقديم دراسة تجريبية بشأن إشارة الرنين في ليزر أشباه الموصلات الشواشي. تعتبر اضطرابات الرنين فعالة في تسخير مؤشرات التذبذب غير الخطية لتطبيقات مختلفة مثل إحداث الشواش والسيطرة على الشواش. تم الحصول على نتائج مثيرة للاهتمام فيما يتعلق بتأثير الرنين الشواشي عن طريق إضافة التردد على الأنظمة. يغير التردد القسري النظام الديناميكي غير الخطي من خلال قيمة حرجة ، وهناك انتقال من جاذب دوري إلى جاذب غريب. كما ان السعة لها تأثير وثيق الصلة للغاية بالنظام ، مما أدى إلى استجابة الرنين الأمثل للقيم المناسبة المتعلقة بزمن الارتباط. فيصبح النظام الشواشي منتظمًا تحت ترددات أو سعات معتدلة. كما تم تحليل هذه الديناميكيات لمخرجات الليزر من خلال السلاسل الزمنية واطياف القدرة المستخرجة (FFT) وقد تعززت بواسطة مخطط التشعب.In this paper, an experimental study has been conducted regarding the indication of resonance in chaotic semiconductor laser. Resonant perturbations are effective for harnessing nonlinear oscillators for various applications such as inducing chaos and controlling chaos. Interesting results have been obtained regarding to the effect of the chaotic resonance by adding the frequency on the systems. The frequency changes nonlinear dynamical system through a critical value, there is a transition from a periodic attractor to a strange attractor. The amplitude has a very relevant impact on the system, resulting in an optimal resonance response for appropriate values related to correlation time. The chaotic system becomes regular under a moderate frequencies or amplitudes. These dynamics of the laser output are analyzed by time series, FFT and bifurcation diagram as a result
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