Paper detail

Simple method for producing Bose-Einstein condensates of metastable helium using a single beam optical dipole trap

We demonstrate a simple scheme to reach Bose-Einstein condensation (BEC) of metastable triplet helium atoms using a single beam optical dipole trap with moderate power of less than 3 W. Our scheme is based on RF-induced evaporative cooling in a quadrupole magnetic trap and transfer to a single beam optical dipole trap that is located below the magnetic trap center. We transfer 1x10^6 atoms into the optical dipole trap, with an initial temperature of 14 μK, and observe efficient forced evaporative cooling both in a hybrid trap, in which the quadrupole magnetic trap operates just below the levitation gradient, and in the pure optical dipole trap, reaching the onset of BEC with 2x10^5 atoms and a pure BEC of 5x10^4 atoms. Our work shows that a single beam hybrid trap can be applied for a light atom, for which evaporative cooling in the quadrupole magnetic trap is strongly limited by Majorana spin-flips, and the very small levitation gradient limits the axial confinement in the hybrid trap.