arXiv subjects

Javier E. Vitela

Publications and source records attributed to Javier E. Vitela.

2 recordsLinked to original sources

arXiv2009

Coherent State Description of the Ground State in the Tavis-Cummings Model and its Quantum Phase Transitions

Quantum phase transitions and observables of interest of the ground state in the Tavis-Cummings model are analyzed, for any number of atoms, by using a tensorial product of coherent states. It is found that this "trial" state constitutes a very good approximation to the exact quantum solution, in that it globally reproduces the expectation values of the matter and field observables. These include the population and dipole moments of the two-level atoms and the squeezing parameter. Agreement in the field-matter entanglement and in the fidelity measures, of interest in quantum information theory, is also found.The analysis is carried out in all three regions defined by the separatrix which gives rise to the quantum phase transitions. It is argued that this agreement is due to the gaussian structure of the probability distributions of the constant of motion and the number of photons. The expectation values of the ground state observables are given in analytic form, and the change of the ground state structure of the system when the separatrix is crossed is also studied.

quant-ph↗

arXiv2004

Stabilization of burn conditions in an ITER FEAT like tokamak with uncertainities in the helium ash confinement time

In this work we demostrate using a two-temperature volume average 0D model that robust stabilization, with regard the hellium ash confinement time, of the burn conditions of a tokamak reactor with the ITER FEAT design parameters can be achieved using Radial Basis Neural Networks (RBNN). Alpha particle thermalization time delay is taken into account in this model. The control actions implemented by means of a RBNN, include the modulation of the DT refueling rate, a neutral He-4 injection beam and auxiliary heating powers to ions and to electrons; all of them constrained to lie within allowable range values. Here we assume that the tokamak follows the IPB98(y,2) scaling for the energy confinement time, while the helium ash confinement time is assumed to be independently estimated on-line. The DT and helium ash confinement times are assumed to keep a constant relationship at all times. An on-line noisy estimation of the helium ash confinement time is simulated by corrupting it with pseudo Gaussian noise.

physics.plasm-ph↗