Sur ce site

Sur le Web du CNRS

Accueil du site > Séminaires > Archives > Année 2010 > Anders Kastberg

A new laboratory at LPMC in Nice for quantum information with cold atoms. A three-dimensional Brownian motor, realized with symmetric optical lattices

Anders Kastberg

Mercredi 27 janvier, à 11h en salle C. Brot

In this talk, I will first briefly give a general presentation of the experimental activity in cold atoms and optical lattices that I have been running at Umea University in Sweden, and which is now moving to LPMC in Nice. This introduction includes a few general ideas about the experiments we have in mind in Nice, associated with quantum storage. The main part of the talk will be devoted to an ongoing project concerning three-dimensional Brownian motors with real-time control, realized with optical lattices.

Brownian motors are systems where isotropic noise and fluctuations are rectified in order to achieve controlled directed motion. In order to accomplish this, the system has to be out of thermal equilibrium (second law of thermodynamics), and somehow spatio-thermal symmetry must be broken (the Curie principle).

We have experimentally implemented a system where cold atoms are trapped in either of two optical lattices, of equal spatial topography, but trapping two different internal states. Inherent in the system are isotropic fluctuations, due to incoherent light scattering, leading to a diffusion, which is typically symmetric. Associated with this scattering is also optical pumping between the two optical lattices, that is, the atom will transfer back and forth between the two internal states and the two respective optical lattices.

If, and only if, we prepare the system in a way, that the transfer between the lattices is asymmetric, and at the same time impose a spatial phase shift between the lattices, we bias the drift and get directed motion in a controllable direction. Since we can control the spatial phase in three dimensions, we are able to demonstrate a three-dimensional Brownian motor, and we have a system where isotropic fluctuations can be used as source for propelling atoms along a predetermined path.

Recently, we have been able to control the 3D Brownian motor along closed, predetermined paths, using only the noise term as the energy input. These results are very preliminary.

This talk will be given in the language : L=a|A>+f|F>+s|S>,

where A, F and S are respectively English, French and Swedish, where a, f and s are complex coefficient, and where |a|² > |f|², |s|².

Anders Kastberg est membre du LPMC.