Cold atoms in Toulouse

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A quasi-monomode guided atom-laser from an all-optical BEC
Spin distillation
An all optical BEC achieved 


Thanks to RF outcoupling, it is already feasible to extract a  coherent matter wave (Fig. 1) from a Bose-Einstein condensate (BEC). Coherent beams obtained in this fashion are nothing but pulsed atom lasers, pulsed in this sense means that one needs to achieve again and again BEC in order to manipulate the outcoupled beam. The major restriction for future developments is the available mean flux of atoms and the limited rate of repetition: actually, to achieve BEC one needs to load a magnetic trap, and then to perform forced evaporative cooling, which takes typically tens of seconds. By contrast, the goal of our experiment is to produce a continuous coherent beam of cold atoms, much more intense than those based on standard BEC.

Fig. 1 : Atom laser gallery 


This experiment, started in september 1999, consists in injecting pre-cooled atoms into a magnetic guide, in order to implement evaporative cooling along the guide. Our aim is to Bose condense atoms in the tranverse ground state of the guide, realizing a monomode beam. This kind of source enables the study of superfluidity in reduced-dimension traps and paves the way for future applications such as nanolithography, metrology,... In figure 2, we summarize different regimes in terms of brightness and phase space density obtained so far for cold atomic beams, where the path when evaporative cooling is applied is marked in green.

Fig 2 : Brightness as a function of phase space density.

Preliminary theoretical studies have been done by our group, they mainly show that a significant gain in brightness is reachable for a magnetic guide of a few meters. Moreover, longitudinal coherence is induced by interactions and can be significantly higher than the de Broglie wavelength. Note furthermore that the expected output flux is of the order of 107 atoms/s, higher by more than two or three orders of magnitude with respect to the mean flux obtained from traditional BEC.

Ref.: Evaporative cooling of an atomic beam, E. Mandonnet, A. Minguzzi, R. Dum, I. Carusotto, Y. Castin, and J. Dalibard, Eur. Phys. J. D 10, 9 (2000).

We acknowledge funds supporting our activity   

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