Bose-Einstein condensation and spin mixtures of optically trapped metastable helium

We report the realization of a Bose-Einstein condensate of metastable helium-$4$ atoms (⁴He{}*$) in an all-optical potential. Up to $10⁵ spin-polarized ⁴He{}*$ atoms are condensed in an optical dipole trap formed from a single, focused, vertically propagating far-off-resonance laser beam. The vertical trap geometry is chosen to best match the resolution characteristics of a delay-line anode microchannel plate detector capable of registering single He* atoms. We also confirm the instability of certain spin-state combinations of ⁴He{}*$ to two-body inelastic processes, which necessarily affects the scope of future experiments using optically trapped spin mixtures. In order to better quantify this constraint, we measure spin-state-resolved two-body inelastic loss rate coefficients in the optical trap.