Bose-Einstein Condensation of Metastable Helium

We have observed a Bose-Einstein condensate in a dilute gas of ^4He in the ^32S₁ metastable state. We find a critical temperature of (4. 70. 5) and a typical number of atoms at the threshold of 810^6. The maximum number of atoms in our condensate is about 510^5. An approximate value for the scattering length a0ex{0ex}=0ex{0ex} (168) nm is measured. The mean elastic collision rate at threshold is then estimated to be about 210^4s^-1, indicating that we are deeply in the hydrodynamic regime. The typical decay time of the condensate is 2s, which places an upper bound on the rate constants for two-body and three-body inelastic collisions.