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BEC of metastable helium

We have observed Bose-Einstein Condensation of metastable helium. In the experiment we trap about 109 atoms in a MOT at 1 mK, spin polarize them and confine about 6 x 108 in a cloverleaf magnetic trap where we cool them to 0.1 mK in optical molasses.

After compression we evaporatively cool the atoms in 30 seconds to BEC. The condensate was first observed on a microchannel plate detector, mounted ~20 cm below the trap centre where the time-of-flight spectrum changed from a Maxwell-Boltzmann distribution to the inverted parabola, characteristic of a Thomas-Fermi distribution.

On January 28 we moved the MCP detector a few centimeters away to allow a vertical probe beam for absorption imaging. On the evening of January 28 we then observed a condensate in an absorption image, showing the transfer from a thermal round cloud above BEC to an elongated cloud below the transition temperature.

More details are on the website.