Metastable helium Bose-Einstein condensate with a large number of atoms

We have produced a Bose-Einstein condensate of metastable helium (⁴He*) containing over 1.5×10⁷ atoms, which is a factor of 25 higher than previously achieved. The improved starting conditions for evaporative cooling are obtained by applying one-dimensional Doppler cooling inside a magnetic trap. The same technique is successfully used to cool the spin-polarized fermionic isotope (³He*), for which thermalizing collisions are highly suppressed. Our detection techniques include absorption imaging, time-of-flight measurements on a microchannel plate detector, and ion counting to monitor the formation and decay of the condensate.