We relate the entropies of ensembles of atoms in optical lattices to atoms in simple traps. We then determine which ensembles of lattice-bound atoms will adiabatically transform into a Bose condensate. This shows a feasible approach to Bose condensation without evaporative cooling.
We describe an all-optical method of making a 87Rb Bose-Einstein condensate (BEC). Atoms are first cooled in an optical lattice and loaded into a crossed dipole trap with $1.06\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ light. Then the density is increased by dynamically reducing the trap size, while the atoms are evaporatively cooled by reducing the light intensity. Every 3.3s, we obtain a nearly pure BEC with $3.5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms in their lowest internal energy state.
Summary form only given. Recently, we have created a Bose condensate of /sup 87/Rb atoms directly in an optical trap formed by tightly focused laser beams. Following initial loading from a laser cooled gas, evaporative cooling through the BEC transition is achieved by simply lowering the depth of the optical trap. Our success is due in part to a high initial phase space density realized in the loading of our optical dipole trap and in part to the tight confinement of the atoms that permits rapid evaporative cooling to the BEC transition in 2 s.
A Bose–Einstein condensate with a large atom number is an important experimental platform for quantum simulation and quantum information research. An optical dipole trap is the a conventional way to hold the ultracold atoms, where an atomic cloud is evaporatively cooled down before reaching the Bose–Einstein condensate. A carefully designed trap depth controlling curve is typically required to realize the optimal evaporation cooling. We present and demonstrate a simple way to optimize the evaporation cooling in a crossed optical dipole trap. A polyline shape optical power control profile is easily obtained with our method, by which a pure Bose–Einstein condensate with atom number 1.73 × 105 is produced. Theoretically, we numerically simulate the optimal evaporation cooling using the parameters of our apparatus based on a kinetic theory. Compared to the simulation results, our evaporation cooling shows a good performance. We believe that our simple method can be used to quickly realize evaporation cooling in optical dipole traps.