{"id":1424,"date":"2008-02-19T20:05:00","date_gmt":"2008-02-19T19:05:00","guid":{"rendered":"https:\/\/gqm.lpl.univ-paris13.fr\/?p=1424"},"modified":"2025-11-02T20:08:29","modified_gmt":"2025-11-02T19:08:29","slug":"seminar-ens-cachan","status":"publish","type":"post","link":"https:\/\/gqm.lpl.univ-paris13.fr\/index.php\/2008\/02\/19\/seminar-ens-cachan\/","title":{"rendered":"Seminar: ENS, Cachan"},"content":{"rendered":"\n<h4 class=\"wp-block-heading\"><strong>R\u00e9alisation exp\u00e9rimentale de la Condensation de Bose Einstein du chrome<\/strong><\/h4>\n\n\n\n<!--more-->\n\n\n\n<div data-wp-interactive=\"core\/file\" class=\"wp-block-file\" style=\"padding-right:var(--wp--preset--spacing--50);padding-left:var(--wp--preset--spacing--50)\"><object data-wp-bind--hidden=\"!state.hasPdfPreview\" hidden class=\"wp-block-file__embed\" data=\"https:\/\/gqm.lpl.univ-paris13.fr\/wp-content\/uploads\/2025\/11\/2008-Talk-LV-Cachan.pdf\" type=\"application\/pdf\" style=\"width:100%;height:600px\" aria-label=\"Embed of 2008 - Talk - LV - Cachan.\"><\/object><a id=\"wp-block-file--media-d1f90e3b-b55a-462f-94ec-bed32409c3f2\" href=\"https:\/\/gqm.lpl.univ-paris13.fr\/wp-content\/uploads\/2025\/11\/2008-Talk-LV-Cachan.pdf\">2008 &#8211; Talk &#8211; LV &#8211; Cachan<\/a><a href=\"https:\/\/gqm.lpl.univ-paris13.fr\/wp-content\/uploads\/2025\/11\/2008-Talk-LV-Cachan.pdf\" class=\"wp-block-file__button wp-element-button\" download aria-describedby=\"wp-block-file--media-d1f90e3b-b55a-462f-94ec-bed32409c3f2\">Download presentation<\/a><\/div>\n\n\n\n<p><strong>S\u00e9minaire pour les \u00e9tudiants de 1 \u00e8re et 2 \u00e8me ann\u00e9e<\/strong><\/p>\n\n\n\n<p>La condensation de Bose Einstein est une transition de phase quantique pr\u00e9vue en 1925 par Albert Einstein, \u00e0 partir des travaux de Satyendra Bose. Lorsque la densit\u00e9 dans l&#8217;espace des phases est suffisamment \u00e9lev\u00e9e, c&#8217;est-\u00e0-dire quand la densit\u00e9 du gaz est assez grande et sa temp\u00e9rature assez basse, la statistique de Bose-Einstein pr\u00e9voit qu&#8217;il se produit une accumulation dans le niveau fondamental en \u00e9nergie. Les atomes qui se retrouvent ainsi tous dans le m\u00eame \u00e9tat quantique forment un nouvel \u00e9tat de la mati\u00e8re, aux propri\u00e9t\u00e9s tr\u00e8s diff\u00e9rentes de celles d&#8217;un ensemble d&#8217;atomes usuel, en particulier au niveau de la coh\u00e9rence.<\/p>\n\n\n\n<p>Depuis 1995, ces condensats sont devenus une r\u00e9alit\u00e9 exp\u00e9rimentale dans le monde de la physique atomique. En utilisant de multiples techniques pour ralentir, pi\u00e9ger, et finalement augmenter la densit\u00e9 dans l&#8217;espace des phases de mani\u00e8re radicale \u2013 processus &#8220;d&#8217;\u00e9vaporation&#8221;-, de nombreux groupes sont arriv\u00e9s \u00e0 condenser diff\u00e9rents atomes (Rb, Na, Li, H, He, K, Cs, Yb, et Cr en 2005). Le chrome pr\u00e9sente un int\u00e9r\u00eat majeur de par ses propri\u00e9t\u00e9s magn\u00e9tiques : son moment magn\u00e9tique dans l&#8217;\u00e9tat fondamental est six fois sup\u00e9rieur aux alcalins, et les interactions magn\u00e9tiques entre atomes, qui sont \u00e0 &#8220;longue port\u00e9e&#8221; et anisotropes, font des condensats de chrome des &#8220;ferrofluides&#8221; aux propri\u00e9t\u00e9s nouvelles.<\/p>\n\n\n\n<p>Si chaque atome a demand\u00e9 de grands efforts exp\u00e9rimentaux pour arriver \u00e0 la condensation, le chrome se r\u00e9v\u00e8le sp\u00e9cialement d\u00e9licat. Il nous a fallu recourir \u00e0 de nombreuses astuces pour exploiter sa structure atomique complexe, et obtenir la condensation d&#8217;une mani\u00e8re originale.<\/p>\n\n\n\n<p>La premi\u00e8re partie de mon s\u00e9minaire sera consacr\u00e9e \u00e0 quelques g\u00e9n\u00e9ralit\u00e9s sur la condensation,&nbsp; et aux sp\u00e9cificit\u00e9s du chrome qui ont suscit\u00e9 le lancement de notre projet. Lors d&#8217;une deuxi\u00e8me partie je d\u00e9crirai les processus de ralentissement et de pi\u00e9geage que nous employons dans notre exp\u00e9rience. Ce sera l&#8217;occasion d&#8217;illustrer un cours de physique atomique. Je me servirai en particulier des notions d&#8217;\u00e9mission stimul\u00e9e \u2013 spontan\u00e9e, de l&#8217;interaction moment magn\u00e9tique- champ magn\u00e9tique, et de la force ressentie par un dip\u00f4le \u00e9lectrique induit.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>R\u00e9alisation exp\u00e9rimentale de la Condensation de Bose Einstein du chrome<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_themeisle_gutenberg_block_has_review":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[263],"tags":[61],"class_list":["post-1424","post","type-post","status-publish","format-standard","hentry","category-oral-presentation","tag-laurent-vernac"],"blocksy_meta":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.4 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Seminar: ENS, Cachan - 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