The work was complicated by the fact that, unlike bosons, fermions cannot occupy the same quantum state at the same time, due to the Pauli exclusion principle, and are therefore limited with regard to cooling mechanisms. At low enough temperature evaporative cooling, an important technique used to reach low enough temperature to create the first BEC's, is no longer effective for fermions. To circumvent this issue, Jin and her team cooled potassium-40 atoms in two different magnetic sublevels. This enabled atoms in different sublevels to collide with each other, restoring the efficacy of evaporative cooling. Using this technique, Jin and her group were able to produce a degenerate Fermi gas at a temperature of about 300 nK, or half the Fermi temperature of the mixture.