Cooperative scattering by cold atoms

We have studied the interplay between disorder and cooperative scattering for the single scattering limit in the presence of a driving laser. Analytical results have been derived and we have observed cooperative scattering effects in a variety of experiments, ranging from thermal atoms in an optical dipole trap, atoms released from a dark MOT and atoms in a BEC, consistent with our theoretical predictions.

Cooperative scattering and radiation pressure force in dense atomic clouds

Atomic clouds prepared in ""timed Dicke"" states, i.e. states where the phase of the oscillating atomic dipole moments linearly varies along one direction of space, are efficient sources of superradiant light emission [Scully et al., Phys. Rev. Lett. 96, 010501 (2006)]. Here, we show that, in contrast to previous assertions, timed Dicke states are not the states automatically generated by incident laser light. In reality, the atoms act back on the driving field because of the finite refraction of the cloud. This leads to nonuniform phase shifts, which, at higher optical densities, dramatically alter the cooperative scattering properties, as we show by explicit calculation of macroscopic observables, such as the radiation pressure force.

Entanglement in the steady state of a collective-angular-momentum (Dicke) model

We model the behavior of an ion trap with all ions driven simultaneously and coupled collectively to a heat bath. The equations for this system are similar to the irreversible dynamics of a collective angular momentum system known as the Dicke model. We show how the steady state of the ion trap as a dissipative many-body system driven far from equilibrium can exhibit quantum entanglement. We calculate the entanglement of this steady state for two ions in the trap and in the case of more than two ions we calculate the entanglement between two ions by tracing over all the other ions. The entanglement in the steady state is a maximum for the parameter values corresponding roughly to a bifurcation of a fixed point in the corresponding semiclassical dynamics. We conjecture that this is a general mechanism for entanglement creation in driven dissipative quantum systems.

Bestimmung kortikaler Dicke mit räumlich hoch- und ultra-hochaufgelöster MRT bei 7 Tesla

Magdeburg, Univ., Fak. für Naturwiss., Diss., 2014

Gravitational constraints of dS branes in an AdS Einstein-Brans-Dicke bulk

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Brane cosmic string compactification in Brans-Dicke theory

We investigate an alternative compactification of extra dimensions using local cosmic string in the Brans-Dicke gravity framework. In the context of dynamical systems it is possible to show that there exist a stable field configuration for the Einstein-Brans-Dicke equations. We explore the analogies between this particular model and the Randall-Sundrum scenario.

A path integral approach to the full Dicke model with dipole-dipole interaction

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Gauss-Codazzi formalism to brane-world within Brans-Dicke theory

We apply the Gauss-Codazzi formalism to brane-worlds within the framework of Brans-Dicke gravity. The compactification is taken from six to five dimensions in order to formalize brane-world models with hybrid compactification in scalar tensor theories.

Thermal phase transitions for Dicke-type models in the ultrastrong-coupling limit

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Path integral approach to the full Dicke model

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Introdução à gravitação de Brans-Dicke

The cosmological standard model needs a deep improvement when compared to recent observational data and also when contrasted with a broad theorical context. Al- ternative theories to General Relativity are possible candidates to reach the expectation Physics of Elementary Particles and Gravitation. Scalar-tensor theories seem to reappear from the ashes of the old work by Jordan corresponding appropriately low power limits of unifying theories. Being the Brans Dicke theory a scalar tensor is conducted a comprehensive study starting from its rst motivations to it s current one it is re flections

Compactificação alternativa de dimensões extras em gravitação de Brans-Dicke

After a brief introduction of some gravitational aspects of the Randall-Sundrum braneworld model as well as of the Brans-Dicke (BD) gravity, we propose two braneworld models using the, local and global, cosmic strings in the BD framework in order to generate all the bulk/brane structure. The final scenario is composed, in both cases, of a warped 4-brane with topology 'R POT. 4' x 'S POT. 1' and one extra dimension transverse to the brane. After that, we analyze the founded models in the scope of the Gauss-Codazzi formalism, with and without the imposition of 'Z IND. 2' symmetry on the brane

Role of Mie scattering in the seeding of matter-wave superradiance

Matter-wave superradiance is based on the interplay between ultracold atoms coherently organized in momentum space and a backscattered wave. Here, we show that this mechanism may be triggered by Mie scattering from the atomic cloud. We show how the laser light populates the modes of the cloud and thus imprints a phase gradient on the excited atomic dipoles. The interference with the atoms in the ground state results in a grating that in turn generates coherent emission, contributing to the backward light wave onset. The atomic recoil "halos" created by the Mie-scattered light exhibit a strong anisotropy, in contrast to single-atom scattering.