The precision and stability of atom interferometers highly depends on the expansion temperature of the atomic ensembles. To achieve long pulse separation times, e.g. in a light pulse atom gravimeter, low expansion rates are necessary to enable high beam splitting contrast and preserve ensembles dense enough to be detectable after long times of free fall. The generation of ultracold atomic ensembles with high repetition rates is therefore a key technique for matter-wave sensors.
Optical dipole traps are a commonly used tool for trapping and cooling neutral atoms. However, typical dipole traps are disadvantaged compared to magnetic traps for example implemented with atom chips, due to their small trapping volume and lower evaporation speed.
In our work we use dynamic time-averaged optical potentials to speed up the generation of large ultracold atomic ensembles and study the feasibility of an all-optical matter-wave lens by rapid decompression of the trap. The latter induces oscillations of the ensemble size, as seen in the animation, and can be applied in each temperature regime reached within our evaporation sequence. This matter-wave lens is used to collimate the expansion of Bose-Einstein condensates, but can also be used to shortcut the duration of evaporative cooling. Finally we estimate the impact on the instability of a cold atom gravimeter for different setups.
Please refer to the article All-optical matter-wave lens using time-averaged potentials for further information.