(Português) Programa de Pós-Graduação em Física da UFSC, Florianópolis

EL PROGRAMA DE POSGRADO EN FÍSICA invita a todos para lo seminario:

Quantum dipolar gases for quantum magnetism  

Laurent Vernac

Laboratoire de Physique des Lasers / Université Paris 13

 Resumen:

 Bose Einstein Condensates (BEC) have been obtained with ultra cold atoms in 1995. In these quantum gases all atoms are in the same quantum state, which gives them unique properties in terms of coherence, and allows for observation of matter interference, superfluidity, or transition from superfluid to Mott insulator states in an optical lattice. I will present experimental results obtained in our group with chromium atoms. Due to the high spin (S=3) in the ground state of chromium, there are large magnetic dipole-dipole interactions (DDIs) between the atoms, which are long range, and anisotropic. They confer specific properties to chromium BECs. For example, the excitation spectrum depends on the direction of the magnetic field: a Cr BEC can be seen as an anisotropic superfluid [1]. DDIs allow as well the change of the magnetization of the sample, which leads to spontaneous depolarization of the BEC at low magnetic fields, and multi-components BECs [2,3]. The main part of my talk will be devoted to the results we have obtained in a 3D optical lattice. We have studied spin exchange dynamics due to DDIs in the Mott insulator state, with one or two atoms per lattice site [4]. Our system is well described by an effective XXZ spin Hamiltonian, with Ising and exchange terms. We thus obtain an interesting system for quantum simulation, which realizes a spin model used in condensed matter physics, with true spin-spin interactions. As correlations build up between the few thousands of atoms loaded in the lattice, our system should reveal as well the existence of entanglement between many particles, through the finding of a relevant experimental entanglement witness. I will conclude by perspectives offered by our recent production of a chromium quantum gas with the fermionic isotope (Fermi Sea) [5].

REFS.:     

[1] Anisotropic Excitation Spectrum of a Dipolar Quantum Bose Gas G. Bismut et al., Phys. Rev. Lett. 109, 155302 (2012)

[2] Spontaneous demagnetization of a dipolar spinor Bose gas atultra-low magnetic field

B. Pasquiou, Phys. Rev. Lett. 106, 255303 (2011)

[3] Thermodynamics of a Bose-Einstein condensate with free magnetization B. Pasquiou et al., Phys. Rev. Lett., 108, 045307 (2012)

[4] Nonequilibrium Quantum Magnetism in a Dipolar Lattice Gas A. de Paz et al., Phys. Rev. Lett., 111, 185305 (2013)

[5] Chromium Dipolar Fermi SeaB. Naylor et al., Phys. Rev. A 91, 011603(R) (2015)

Fecha: 6 de marzo de 2015 – (viernes) – Lugar: Sala 212 Auditorio del Departamento de Física – Horário: 10h15min

EL PROGRAMA DE POSGRADO EN FÍSICA invita a todos para lo seminario:

Correlating Structural, Electronic and Ionic Diffusion Properties of Nanomaterials for Energy Storage  

Profª Drª Corinne Arrouvel / UFSCar – Sorocaba

Resumen:

The quest of new materials at the nanoscale is an important topic in the modern society. The industrial interest is to improve the energy conversion, the storage capacity and the kinetic of the electrochemical energy in high-technology devices. Materials should be in addition low cost, stable under a wide range of temperature and pressure conditions and safe. This talk will introduce basic concepts of electrochemistry, of bulk and surface properties in order to explain the difference of energy carrier transport mechanisms in rechargeable lithium batteries, capacitors, solid oxide fuel cells and solar cells. Combining computational and experimental techniques, we show that some key aspects are based on the search of optimized size and morphology of their nanocomponents. Anisotropic energy pathways and crystal shape will be therefore highlighted.

Fecha: 5 de dezembro de 2014 – (viernes) – Lugar: Sala 212 Auditorio del Departamento de Física – Horário: 10h15min

 EL PROGRAMA DE POSGRADO EN FÍSICA invita a todos para lo seminario:

Nonperturbative QCD effects in forward scattering at LHC  

Prof. Emerson Gustavo de Souza Luna – IF/UFRGS

Resumen:

We study infrared contributions to semihard parton-parton interactions by considering an effective charge whose finite infrared behavior is constrained by a dynamical mass scale. Using an eikonal QCD-based model in order to connect this semihard parton-level dynamics to the hadron-hadron scattering, we obtain predictions for the proton-proton ($pp$) and antiproton-proton ($\bar{p}p$) total cross sections, $\sigma_{tot}^{pp,\bar{p}p}$, as well as for the ratios of the real to imaginary part of the forward scattering amplitude, $\rho^{pp,\bar{p}p}$. We discuss the theoretical aspects of this formalism and consider the phenomenological implications of a class of energy-dependent form factors in the high-energy behavior of the forward amplitude. Our results, obtained using a group of updated sets of parton distributions, are consistent with the recent data from the TOTEM experiment.

Fecha: 28 de noviembre de 2014 – (Viernes) – Lugar: Sala 212 Auditorio del Departamento de Física – Horário: 10h15min