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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.


Metastable Helium BEC

The G-10 cell and trapping magnets.
Phase-contrast images of 4He* in 1 ms TOF, showing BEC formation. (a) a thermal cloud slightly above Tc. (b) onset of BEC. (c) a nearly pure BEC after further evaporative cooling.

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 from a 4He buffer gas with an efficiency of 10^-5 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.

Click here for 2009 GRC poster:He_BEC_GRC_2009_poster.pdf

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.

Recent Publications

  1. Large spin relaxation rates in trapped submerged-shell atoms, C. B. Connolly, Y. S. Au, S. C. Doret, W. Ketterle, J. M. Doyle. Phys. Rev. A 81, 010702(R) (2010).
  2. Buffer-gas cooled Bose-Einstein condensate, S. C. Doret, C. B. Connolly, W. Ketterle, and J. M. Doyle. PRL 103, 103005 (2009).
  3. Spin-exchange collisions of submerged shell atoms below 1 kelvin, J.G.E. Harris, S.V. Nguyen, S.C. Doret, W. Ketterle, and J.M. Doyle. Physical Review Letters, 99, 223201 (2007).
  4. Evaporative cooling of metastable helium in the multi-partial-wave regime, S.V. Nguyen, S.C. Doret, C.B. Connolly, R.A. Michniak, W. Ketterle, and J.M. Doyle. Phys. Rev. A, 72, 060703(R) (2005).