Three Peaks Gallery




 

Observation of Bose-Einstein condensation by absorption imaging. Shown is absorption vs. two spatial dimensions. The Bose-Einstein condensate is characterized by its slow expansion observed after 6 msec time of flight. The left picture shows an expanding cloud cooled to just above the transition point; middle: just after the condensate appeared; right: after further evaporative cooling has left an almost pure condensate. The width of the images is 1.0 mm. The total number of atoms at the phase transition is about 7x10^5, the temperature at the transition point is 2 microK.

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Gaussian velocity profiles These three peaks are plots of the optical density of three different clouds of sodium atoms. The data was taken after the gas had been allowed to freely expand for several milliseconds. The images were taken at three different temperatures: one just above the transition temperature, one just below the transition temperature, and one well below the transition temperature.

These "time of flight" images show us the velocity distribution of our atoms. Above the transition temperature, as expected, the velocity distribution is a spherical gaussian. But as we cross the transition line, we see a sudden change. The distribution becomes bimodal, with two separate contributions from the ground state and from all other states. In the third picture, the temperature has been lowered enough so that most of the atoms are in the ground state, and the distribution look gaussian again.

The shadows of the three peaks have been projected onto a screen which shows least squares gaussian fits to the data. It is easy to see that the middle picture represents a bimodal velocity distribution.

(Image rendered with the POV-Ray raytracer by Dallin S. Durfee)