Bose-Einstein condensation of 86Sr
Strontium has three bosonic isotopes, 84Sr, 86Sr, and 88Sr. 84Sr and 88Sr have recently been cooled to quantum degeneracy, but Bose-Einstein condensation (BEC) of 86Sr has so far been elusive. The success of the cooling scheme used to reach quantum degeneracy, evaporative cooling, depends on the ratio of elastic to inelastic collisions. Here 86Sr poses a challenge, since it's scattering length is large, +800 Bohr, and leads to strong three-body loss. The ratio of elastic to inelastic collisions can be improved by reducing the density of the gas. Here we show that it is possible to produce a BEC of 86Sr by performing evaporative cooling at very low densities in a large-volume dipole trap. This BEC enriches the possibilities opened up by strontium quantum gases, for example by providing another isotope for the search of alkali/strontium Feshbach resonances that can be used for molecule creation.
Figure 1:Absorption images and integrated density profiles showing the BEC phase transition for different times tev of the evaporative cooling ramp. The images are taken 25ms after release from the trap and the field of view is 400 × 400 μm2. The solid line represents a fit with a bimodal distribution, while the dashed line shows the Gaussian-shaped thermal part, from which the given temperatures are derived. The nearly pure BEC at 4.7s of evaporation contains about 5000 atoms.
Simon Stellmer, Meng Khoon Tey, Rudolf Grimm and Florian Schreck