Browsing by Author "Mendonça, J. T."
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- Collective processes in a large atomic laser cooling experimentPublication . Rodrigues, J. D.; Rodrigues, J. A.; Ferreira, A. V.; Mendonça, J. T.We introduce an hydrodynamic description of a laser cooled gas. In large traps, with as much as 10(10) atoms, multiple scattering of light leads to a collective interaction field which can be described by a Poisson-like equation, included in our formulation. A behaviour similar to a one-component trapped plasma should then be observed. By considering equilibrium conditions we extract the theoretical atomic density profiles and, in particular, its dependence on the effective plasma frequency of the system. The model is compared with experimentally measured profiles with an extraordinary agreement, thus corroborating both the plasma nature of the dynamics in the gas as well as the validity of the hydrodynamic formulation introduced here.
- Information compression at the turbulent phase transition in cold-atom gasesPublication . Giampaoli, R.; Figueiredo, J. L.; Rodrigues, J. D.; Rodrigues, José-António; Terças, H.; Mendonça, J. T.The statistical properties of physical systems in thermal equilibrium are blatantly different from their far-from -equilibrium counterparts. In the latter, fluctuations often dominate the dynamics and might cluster in ordered patterns in the form of dissipative coherent structures. Here, we study the transition of a cold atomic cloud, driven close to a sharp electronic resonance, from a stable to a turbulent phase. From the atomic density distribution- measured using a spatially resolved pump-probe technique-we have computed the Shannon entropy on two different basis sets. Information compression, corresponding to a minimum in the Shannon entropy, has been observed at criticality, where the system fluctuations organize into high-order (low-entropy) patterns. Being independent of the representation used, this feature is a property shared by a vast class of physical systems undergoing phase transitions.
- Photon bubble turbulence in cold atom gasesPublication . Giampaoli, R.; Rodrigues, João D.; Rodrigues, José-António; Mendonça, J. T.Turbulent radiation flow is commonplace in systems with strong, incoherent, light-matter interactions. In astrophysical contexts, photon bubble turbulence is considered a key mechanism behind enhanced radiation transport, and its importance has been widely asserted for a variety of high energy objects such as accretion disks and massive stars. Here, we show that analogous conditions to those of dense astrophysical objects can be obtained in large clouds of cold atoms, prepared in a laser-cooling experiment, driven close to a sharp electronic resonance. By accessing the spatially-resolved atom density, we are able to identify a photon bubble instability and the resulting regime of photon bubble turbulence. We also develop a theoretical model describing the coupled dynamics of both photon and atom gases, which accurately describes the statistical properties of the turbulent regime. This study thus opens the possibility of simulating radiation-dominated astrophysical systems in cold atom experiments.