Etude des techniques de production de condensats de Bose-Einstein

Download or read book Etude des techniques de production de condensats de Bose-Einstein written by Guillaume Delannoy and published by . This book was released on 2001 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis discusses several topics concerning Bose-Einstein condensation. We present two alternative techniques to produce Bose condensates and an application of the condensates : atom lasers. Our experimental setup uses an iron-core electromagnet to generate a magnetic trap. The magnetic field strength at the center of the trap is of the order of one hundred Gauss. With such a large bias field, radio-frequency-induced evaporative cooling is found to be hampered, and eventually interrupted, by the presence of nonlinear Zeeman shifts. To solve this problem, we use a multi-frequency evaporation scheme. We have also produced Bose-Einstein condensates simultaneously in two internal states by sympathetic cooling. A thermodynamic model allows us to understand the different scenarios observed experimentally. Furthermore, a calculation of the thermalization rate via elastic collisions gives a condition for the two components to stay in thermal contact during the sympathetic cooling process. Finally, we have produced and studied atomic beams generated by rf-output coupling of ultra-cold atomic clouds. With our high magnetic field, the relative stability required to obtain continuous beams is about 10-4. When the magnetic field is not stable enough, we show that a modulation of the frequency or of the amplitude of the rf field allows to stabilize the flux of the atom laser.