Buffer gas cooling and trapping of atoms with small effective magnetic moments

– We have extended buffer gas cooling to trap atoms with small effective magnetic moments μeff . For μeff ≥ 3μB, 10 atoms were buffer gas cooled, trapped, and thermally isolated in ultra high vacuum with roughly unit efficiency. For μeff < 3μB, the fraction of atoms remaining after full thermal isolation was limited by two processes: wind from the rapid removal of the buffer gas and desorbing helium films. In our current apparatus we trap atoms with μeff ≥ 1μB, and thermally isolate atoms with μeff ≥ 1.8μB. This triples the number of atomic species which can be buffer gas cooled and trapped in thermal isolation. Extrapolation of our results and simulations of the loss processes indicate that it is possible to trap and evaporatively cool 1μB atoms using buffer gas cooling. Buffer gas cooling is a powerful tool for producing cold atoms [1]. It relies only upon elastic collisions with a cryogenic helium vapor for cooling, and so is applicable to any atomic species. This is crucial because other methods of cooling (e.g., laser cooling [2] or cooling via superfluid walls [3]) are applicable to only a limited range of species, nearly all of which are S-state atoms whose interactions are dominated by spherically symmetric, short-range potentials (the one exception is Cr, for which magnetic dipolar interactions play a significant role [4]). The production of cold, non-S-state atoms and atoms with a variety of magnetic dipole moments would allow the study of new regimes of atomic collisions [5]. Because many of the properties of a degenerate gas are determined by the collisional properties of its constituents, Bose-condensing these atoms has been predicted to result in qualitatively new types of quantum fluids [6]. The wide applicability of buffer gas cooling also means that it can be used to create cold samples of atoms which are of interest for high-precision spectroscopy but which cannot be laser cooled [7]. It is also capable of cooling arbitrary mixtures of different species and isotopes. Lastly, buffer gas cooling combines these advantages with the ability to produce orders-of-magnitude larger samples of cold atoms than laser cooling. Regardless of the atomic species, larger samples provide improved sensitivity (e.g., for atom interferometers and precision spectroscopy), and lead to new regimes of hydrodynamic quantum gases [8].