Abstract
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 \mu K, 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.
Highlights
Quantum-degenerate atomic gases in optical dipole traps provide the starting point of many experiments
We have measured the number of loaded atoms for different initial optical dipole trap (ODT) powers in order to investigate to what extent we are limited by our maximum ODT power of
We have achieved Bose–Einstein condensation (BEC) of metastable triplet helium atoms via RF-induced evaporative cooling in a quadrupole magnetic trap, transferred to a single-beam hybrid trap, and subsequent evaporative cooling in both the hybrid trap and pure optical dipole trap, using only moderate ODT power of less than 3 W
Summary
Quantum-degenerate atomic gases in optical dipole traps provide the starting point of many experiments To realize these samples, one can directly load a laser-cooled sample into an optical dipole trap (ODT) and perform evaporative cooling, which requires very high ODT powers to provide sufficient trap volume, depth and confinement. One loads the atoms first in a magnetic trap and performs evaporative cooling and afterward transfers a dense and compact atomic cloud into an ODT, which requires a much lower ODT power, at the expense of experimental complexity. Within this last category, a very elegant approach is the hybrid trap (HT), introduced in Ref. By switching off the QMT completely, the atoms are transferred from the HT to a pure ODT
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