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Search Results: 1 - 10 of 306059 matches for " L. O. Casta?os "
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Steady-state quantum correlations of two driven qubits collectively interacting with a vacuum reservoir
L. O. Castaos
Mathematics , 2011,
Abstract: We consider two two-level atoms fixed at different positions, driven by a monochromatic laser field, and interacting collectively with the vacuum electromagnetic field. A Born-Markov-secular master equation is used to describe the dynamics of the two atoms and their steady-state is obtained analytically for two configurations, one in which the atoms are in equivalent positions and another in which they are not. The steady-state populations of the energy levels of the free atoms, entanglement, quantum discord and degree of mixed-ness are calculated analytically as a function of the laser field intensity and the distance between the two atoms. It is found that driving both atoms with the laser field is inefficient for the generation of steady-state correlations when they are in equivalent positions. On the contrary, inequivalent positions lead to the possibility of considerable steady-state entanglement and left/right quantum discord. It is shown that an X-state can be obtained for high laser field intensities for both configurations. This allows the comparison of two measures of quantum discord. The behaviour and relationships between correlations are studied and several limiting cases are investigated.
Velocity selector with a microwave magnetic dipole transition
L. O. Castaos,E. Gomez
Physics , 2014, DOI: 10.1103/PhysRevA.89.013406
Abstract: We proposed a method based on microwave magnetic dipole transitions to prepare samples of atoms with well defined position and velocity. Each microwave pulse corresponds to a position measurement for the atoms and two pulses separated by a given delay result in a velocity measurement. The method gives velocity sensitivity approaching that obtained with Raman transitions but it is easier to implement. Moreover, it has the advantages that it also selects in position and has less demanding experimental requirements. The method can be demonstrated in a magneto-optical trap.
Linear Time-Dependent Invariants for Scalar Fields and Noether's Theorem
O. Castaos,R. López-Pe?a,V. I. Man'ko
Physics , 1994, DOI: 10.1142/S0217732394001635
Abstract: The infinite number of time-dependent linear in field and conjugated momenta invariants is derived for the scalar field using the Noether's theorem procedure.
Squeezing in a 2-D generalized oscillator
O. Castaos,R. López-Pe?a,V. I. Man'ko
Physics , 1994,
Abstract: A two-dimensional generalized oscillator with time-dependent parameters is considered to study the two-mode squeezing phenomena. Specific choices of the parameters are used to determine the dispersion matrix and analytic expressions, in terms of standard hermite polynomials, of the wavefunctions and photon distributions. (to be publish in the Third Workshop on Squeezed States and Uncertainty Relations, Baltimore, USA, (August 1993))
Noether's Theorem and time-dependent quantum invariants
O. Castaos,R. López-Pe?a,V. I. Man'ko
Physics , 1994, DOI: 10.1088/0305-4470/27/5/035
Abstract: The time dependent-integrals of motion, linear in position and momentum operators, of a quantum system are extracted from Noether's theorem prescription by means of special time-dependent variations of coordinates. For the stationary case of the generalized two-dimensional harmonic oscillator, the time-independent integrals of motion are shown to correspond to special Bragg-type symmetry properties. A detailed study for the non-stationary case of this quantum system is presented. The linear integrals of motion are constructed explicitly for the case of varying mass and coupling strength. They are obtained also from Noether's theorem. The general treatment for a multi-dimensional quadratic system is indicated, and it is shown that the time-dependent variations that give rise to the linear invariants, as conserved quantities, satisfy the corresponding classical homogeneous equations of motion for the coordinates.
Variational Formulation of Linear Time-Dependent Invariants
O. Castaos,R. López-Pe?a,V. I. Man'ko
Physics , 1994,
Abstract: It is shown that linear time-dependent invariants for arbitrary multi\-dimensional quadratic systems can be obtained from the Lagrangian and Hamiltonian formulation procedures by considering a variation of coordinates and momenta that follows the classical trajectory and defines a noetherian symmetry transformation.
On the Superradiant Phase in Field-Matter Interactions
O. Castaos,E. Nahmad-Achar,R. López-Pe?a,J. G. Hirsch
Physics , 2011, DOI: 10.1103/PhysRevA.84.013819
Abstract: We show that semi-classical states adapted to the symmetry of the Hamiltonian are an excellent approximation to the exact quantum solution of the ground and first excited states of the Dicke model. Their overlap to the exact quantum states is very close to 1 except in a close vicinity of the quantum phase transition. Furthermore, they have analytic forms in terms of the model parameters and allow us to calculate analytically the expectation values of field and matter observables. Some of these differ considerably from results obtained via the standard coherent states, and by means of Holstein-Primakoff series expansion of the Dicke Hamiltonian. Comparison with exact solutions obtained numerically support our results. In particular, it is shown that the expectation values of the number of photons and of the number of excited atoms have no singularities at the phase transition. We comment on why other authors have previously found otherwise.
A semi-classical versus quantum description of the ground state of three-level atoms interacting with a one-mode electromagnetic field
S. Cordero,O. Castaos,R. López-Pe?a,E. Nahmad-Achar
Mathematics , 2013, DOI: 10.1088/1751-8113/46/50/505302
Abstract: We consider $N_a$ three-level atoms (or systems) interacting with a one-mode electromagnetic field in the dipolar and rotating wave approximations. The order of the quantum phase transitions is determined explicitly for each of the configurations $\Xi$, $\Lambda$ and $V$, with and without detuning. The semi-classical and exact quantum calculations for both the expectation values of the total number of excitations $\cal{M}=\langle \bm{M} \rangle$ and photon number $n=\langle \bm{n} \rangle$ have an excellent correspondence as functions of the control parameters. We prove that the ground state of the collective regime obeys sub-Poissonian statistics for the ${\cal M}$ and $n$ distribution functions. Therefore, their corresponding fluctuations are not well described by the semiclassical approximation. We show that this can be corrected by projecting the variational state to a definite value of ${\cal M}$.
Transporte y consumo de otras durante la romanización en el norte de la Península Ibérica
Castaos, P.,Escribano, O.
Munibe Antropologia-Arkeologia , 2010,
Abstract: En este trabajo se estudia la presencia de ostras en yacimientos alejados de la costa durante la Romanización en el Norte de la Península Ibérica. Se establece una metodología para la estimación del número mínimo de individuos y la osteometría de esta especie. Se comprueba la importancia cuantitativa del consumo de este molusco en la dieta. Se aborda experimentalmente el problema del transporte de las ostras desde la costa hasta asentamientos de interior. Se establecen las ventajas de las distintas formas de colocación y del grado supervivencia de los animales durante el tiempo de transporte.
Características clínicas e histopatológicas del síndrome nefrótico primario
Bola?os,Laercio; Castao,Iris de;
Colombia Médica , 2005,
Abstract: introduction: the presentation of nephrotic syndrome with severe proteinuria, hypoalbuminemia, generalized edema and his treatment with high-dose of steroides, force the clinicial to recognize and treat opportunely. also must have the ability to predict the outcome and prognosis of the disease after the initial treatment. objectives: to know the behavior of primary nephrotic syndrome in children in cali and peripheral areas, the demographic profiles, the clinical presentation, the response to treatment the histopathology classification and recommendation for renal biopsy. design and methods: from january 1986 to july 2002, 264 medical records of children with primary nephrotic syndrome between 1 to 15 years old were reviewed. results: the mean age for the diagnosis was 4 years, 60% of the patients were males and 40% females. all the patients presented with edema and massive proteinuria, 97% hypoalbuminemia, 94% hypercholesterolemia and 54% oliguria. the response to therapy with corticosteroids was 89% and 11% were corticoresistent: this percentage is lower than other series which report up to 30% corticosteroid resistence. in 65 patients with frequent relapsing we observed good response to cyclophosfamide in 40%. renal biopsy was performed in 73 patients; the indication for the biopsy was no response to steroid therapy in 29%, frequent relapses and steroid dependence in 71%. the diagnosis in these 73 biopsies was minimal changes 36%, mesangial proliferation 46%, focal segmental glomeruloesclerosis 11%, and other pathologies 7%. conclusions: we observed low frequency of corticosteroid resistence patients and focal segmental glomeruloesclerosis than other series. we recommend the use of cyclophosfamide in frequent relapsing patients before doing a renal biopsy. renal biopsy is recommended in corticoid resistent patients. only 40% of the patients had complete follow up in nephrology outpatient clinic. it is important to improve follow up of nephrotic patients.
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