Non-resonant inter-species interaction and its effect on the position response function of cold atoms

In the context of non-equilibrium statistical physics, the position response of a particle, coupled to a bath, subjected to an external force is a topic of broad interest. A topic of further interest is two distinguishable sets of interacting particles in contact with two distinct baths. Here, we report the experimental evidence of the modification of the position response function (PRF) of an ensemble of cold atoms in a magneto-optical trap when it is placed alongside a dilute cloud of cold atoms of a different species. Our experiment consists of a mass-imbalanced cold atomic mixture of ³⁹K and ²³Na atoms. We focus on the position response of ³⁹K atoms when subjected to a sudden displacement in the presence of a cold ²³Na atomic cloud. Notably, we find that, in the underdamped regime of motion, the oscillation frequency of motion of the cold atoms changes as much as 30 % depending on the effective inter-species light-assisted interaction strength. On the other hand, in the overdamped regime, there is a reduction, as high as 10.5 %, in the damping coefficient, depending on the interaction strength. Using a generalized quantum Langevin approach, we develop a theoretical framework, compare it with the experimental results, and find good agreement. Our results are expected to find applications in the domain of mass and charge transport studies in a wide variety of physical conditions, which can be simulated in cold atom experiments.