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Claude Cohen Tannoudji

Prix Nobel en 1997 pour le ralentissement et le piégeage des atomes par la lumière laser.

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Accueil du site > Séminaires > LKB > Séminaire « atomes froids LKB » : Spin fragmentation of a Bose-Einstein condensate with antiferromagnetic interactions

Séminaire « atomes froids LKB » : Spin fragmentation of a Bose-Einstein condensate with antiferromagnetic interactions

Séminaire de Vincent Corre

Mercredi 26 mars 2014 de 14h a 15h, en salle 235A au 29 rue d’Ulm 75005 Paris.

We experimentally study the properties of a Sodium spin-1 Bose-Einstein condensate with antiferromagnetic interactions. We investigate the equilibrium phase diagram of the system and find good quantitative agreement with mean-field theory.

We further study the behavior of the system at small magnetic fields and small magnetization where mean-field theory breaks down and anomalously large fluctuations are observed. We show that they can be explained by collective spin fluctuations, that would vanish in the thermodynamic limit but are important due to the small size (atom number few thousands) of the samples we study.

This illustrates on a particular example how fluctuations in small systems are effective to counter symmetry breaking. We use the two first moments (mean and variance) of the population in mz=0 to reveal the evolution of the system from a fragmented condensate to a regular mean-field state as the quadratic Zeeman effect increases.

We are able to infer the temperature associated to the spin degree of freedom from these two moments, and independently from the distribution of the mz=0 population. We find good agreement between the two methods.

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