3,736 research outputs found
A robust one-step catalytic machine for high fidelity anti-cloning and W-state generation in a multi-qubit system
We propose a physically realizable machine which can either generate
multiparticle W-like states, or implement high fidelity () anti-cloning of an arbitrary qubit state, in a single step. Moreover
this universal machine acts as a catalyst in that it is unchanged after either
procedure, effectively resetting itself for its next operation. It also
possesses an inherent {\em immunity} to decoherence. Most importantly in terms
of practical multi-party quantum communication, the machine's robustness in the
presence of decoherence actually {\em increases} as the number of qubits
increases.Comment: 4 pages, 2 figure
Ultrafast deterministic generation of entanglement in a time-dependent asymmetric two-qubit-cavity system
We present an efficient scheme for the controlled generation of pure
two-qubit states possessing {\em any} desired degree of entanglement and a {\em
prescribed} symmetry in two cavity QED based systems, namely, cold trapped ions
and flying atoms. This is achieved via on-resonance ion/atom-cavity couplings
which are time-dependent and asymmetric, leading to a trapping vacuum state
condition which does not arise for identical couplings. A duality in the role
of the coupling ratio yields states with a given concurrence but opposing
symmetries. The experimental feasibility of the proposed scheme is also
discussed.Comment: 4 pages, 4 figure
On the 2D Dirac oscillator in the presence of vector and scalar potentials in the cosmic string spacetime in the context of spin and pseudospin symmetries
The Dirac equation with both scalar and vector couplings describing the
dynamics of a two-dimensional Dirac oscillator in the cosmic string spacetime
is considered. We derive the Dirac-Pauli equation and solve it in the limit of
the spin and the pseudo-spin symmetries. We analyze the presence of cylindrical
symmetric scalar potentials which allows us to provide analytic solutions for
the resultant field equation. By using an appropriate ansatz, we find that the
radial equation is a biconfluent Heun-like differential equation. The solution
of this equation provides us with more than one expression for the energy
eigenvalues of the oscillator. We investigate these energies and find that
there is a quantum condition between them. We study this condition in detail
and find that it requires the fixation of one of the physical parameters
involved in the problem. Expressions for the energy of the oscillator are
obtained for some values of the quantum number . Some particular cases which
lead to known physical systems are also addressed.Comment: 15 pages, 8 figures, matches published versio
Dynamics of quantum correlations and linear entropy in a multi-qubit-cavity system
We present a theoretical study of the relationship between entanglement and
entropy in multi-qubit quantum optical systems. Specifically we investigate
quantitative relations between the concurrence and linear entropy for a
two-qubit mixed system, implemented as two two-level atoms interacting with a
single-mode cavity field. The dynamical evolutions of the entanglement and
entropy, are controlled via time-dependent cavity-atom couplings. Our
theoretical findings lead us to propose an alternative measure of entanglement,
which could be used to develop a much needed correlation measure for more
general multi-partite quantum systems.Comment: New discussions on the generality of entanglement-entropy
relationship, one new reference, and other minor changes. 10 pages, 6
figures, accepted for publication in J.Opt. B: "Special Issue on Fluctuations
& Noise in Photonics & Quantum Optics.
Fundamentals and Applications of Surface-Enhanced Raman Spectroscopy (SERS)
When a molecule is adsorbed on some metallic nanostructured surfaces such as silver, copper or gold, it can undergo an enormous enhancement of the Raman signal giving rise to the so called Surface-Enhanced Raman Scattering (SERS). The high sensitivity of this effect allows an accurate structural study of adsorbates at very low concentrations. The SERS effect has historically been associated with the substrate roughness on two characteristic length scales. Surface roughness on the 10 to 100 nm length scale supports localized plasmon resonances which are considered as the dominant enhancement mechanism of SERS (Electromagnetic Enhancement Mechanism: SERS-EM). It is usually accepted that these electromagnetic resonances can increase the scattered intensity by an average factor of ca. 104 to 107. A secondary mechanism often thought to require atomic scale roughness is referred to as Charge Transfer (CT) Enhancement Mechanism (SERS-CT). This mechanism involves the photoinduced transfer of an electron from the metal to the adsorbate or vice versa and involves new electronic excited CT states which result from adsorbate–substrate chemical interactions. It is also estimated that such SERS-CT mechanism can enhance the scattering cross-section by a factor of ca. 10 to 102. These two mechanisms can operate simultaneously, depending on the particular systems and experimental conditions, making difficult to recognize each one and to estimate their relative magnitude in a particular spectrum.Universidad de Málaga. Campus de Excelencia Internacional AndalucÃa Tech
El conocimiento didáctico-matemático: una propuesta de evaluación de tres de sus facetas
En esta comunicación se presentan algunos criterios tenidos en cuenta para el diseño de un cuestionario para evaluar tres facetas del conocimiento matemático para la enseñanza de la derivada: el conocimiento común del contenido, el conocimiento especializado y el conocimiento ampliado. Asà mismo se presenta una tarea propuesta en el cuestionario aplicado a estudiantes de las licenciaturas en Básica Matemáticas y Matemáticas -FÃsica de la Universidad de Antioquia, Colombia
Un modelo de análisis del conocimiento didáctico-matemático: el caso de la formación inicial de profesores sobre la derivada
En este trabajo se presenta una propuesta de caracterización del conocimiento didáctico-matemático, sobre la derivada, que un profesor de matemáticas necesita para efectuar eficientemente su práctica. Se ilustra el uso del enfoque ontosemiótico del conocimiento y la instrucción matemática (EOS) para responder a cuestiones tales como: ¿Cómo o bajo qué criterios puede ser evaluado el Conocimiento Didáctico-Matemático? ¿Cómo se relacionan los distintos componentes del Conocimiento Didáctico-Matemático? ¿Cómo los formadores de profesores pueden ayudar a los futuros profesores a desarrollar los distintos componentes del Conocimiento Didáctico-Matemático? En este trabajo, se responde, aunque de manera parcial, a dichas preguntas, mediante el planteamiento de criterios especÃficos que, por medio de un cuestionario, permiten explorar el conocimiento común, especializado y ampliado del contenido de futuros profesores de bachillerato sobre la derivada
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