BEC
Contents
Overview
Despite innumerable experimental advances, research with degenerate Bose and Fermi gases has remained limited to only a handful of atomic species since its inception due to the field's reliance on laser pre-cooling as the first step towards quantum degeneracy. Developmening new cooling methods applicable to a wider range of atoms and also to molecules and extendable to the ultracold regime is thus important for taking full advantage of scientific opportunities in new areas.
People
- Charlie Doret
- Colin Connolly
- Yat Shan Au
Metastable Helium BEC
We have utilized buffer-gas methods to demonstrate Bose-Einstein condensation of 4He* without the use of laser pre-cooling. These methods are readily extendable to any paramagnetic species with typical collisional parameters that allow for efficient evaporative cooling, significantly extending the scope of ultracold atom/molecule research. The experiment takes place in a G-10 cell, coaxially inside the bore of a 4 T deep superconducting anti-Helmholtz magnetic trap and thermally anchored to a dilution refrigerator. 4He* is excited via RF discharge with an efficiency of 10^-5 from a 4He buffer gas and cooled to the refrigerator temperature by collisions with the remaining buffer gas. The buffer gas is cryo-pumped to a charcoal sorb, leaving approximately 10^11 4He* atoms trapped in the magnetic field. The atom cloud is then evaporatively cooled to 1 mK by surface-induced evaporation, forced by asymmetrically reducing the currents to the anti-Helmholtz coils. Atoms are then transferred to a tightly confining, superconducting quadrupole-Ioffe configuration (QUIC) trap to prevent Majorana losses. After transferring the atoms evaporative cooling continues, now using an RF knife. In the present apparatus we observe BEC formation at a temperature of 5 uK with approximately 10^6 atoms remaining, while further evaporative cooling create nearly-pure condensates of 2-300,000 atoms. Geometric constraints currently limit the transfer of atoms to the QUIC trap to 5% efficiency; straightforward improvements should produce condensates of 10^7 atoms.
2009 GRC poster:Media:GRC_poster
Two-body collisions in Thulium and Erbium
Since producing our 4He* BEC we have been investigating two-body atom-atom collisional properties of the "submerged-shell" rare-earth atoms Thulium and Erbium using the same apparatus. Previous research in our lab indicated that the submerged-shell nature of these atoms gives rise to strong suppression of inelastic processes during atom-helium collisions. Similar suppression of inelastic collisions in atom-atom collisions would permit efficient evaporative cooling and make these atoms excellent candidates for new quantum degenerate gases, accessible using our new buffer-gas BEC approach.
