Efficient atomic lensing of quantum gas mixtures

Abstract

Mixtures of ultracold quantum gases are at the heart of currently planned high-precision quantum tests of the weak equivalence principle, where dual-species Bose-Einstein condensates are probed with atom interferometry techniques. An important challenge for such experiments is to reach very low expansion velocities by means of time-dependent potentials acting as matter-wave lenses while ensuring the co-location of the two atomic species and matching their expansion rates during the whole free evolution. To achieve the required control, one lensing pulse is needed for each independent spatial direction and atomic species, which makes a full 3D implementation rather impractical.

Here we propose to overcome these challenges by taking advantage of special magic wavelengths for optical dipole traps where the ratio of the optical potentials is given by the ratio of the masses of the different species. In this case the center-of-mass dynamics is identical for all species, resulting in a perfect co-location of the mixture even in an Earth-based laboratory. Most importantly, optical dipole traps with such a magic laser wavelength give riseto a common expansion dynamics for both species and therefore guarantee that the relative shape of the mixture is conserved during the entire evolution, including when the lensing potentials are applied. Hence, our approach enables an efficient collimation of mixtures of ultracold atoms in order to reach the very low expansion rates that are necessary for highprecision measurements while cutting in half the number of required lensing pulses compared to standard approaches.