Imaging of Rydberg Impurities in an Ultracold Atomic Gas

Abstract

This thesis investigates how a single highly excited atom, called Rydberg atom, can be optically imaged. Direct detection methods based on the scattering of light are hardly applicable due to the small scattering rate of the ground to Rydberg state transition. Instead, a cloud of ground state atoms, normally absorptive, is rendered transparent using electromagnetically induced transparency (EIT), involving an auxiliary probe Rydberg state. The cloud acts as a contrast medium, whose optical response is locally perturbed by the strong Rydberg-Rydberg interaction between the probe and the Rydberg impurity which we want to detect. This perturbation restores absorption within a small volume around the impurity, readily detected and spatially resolved on a camera. We call this technique Interaction Enhanced Imaging (IEI). To implement IEI we characterize the optical response of the EIT contrast medium in absence of interactions. By combining measurements of the spatially resolved optical spectrum and of the total Rydberg atom number, we can reconstruct the full one-body density matrix of the three-level system. Next, we excite |nS> or |nP> states and, using IEI, we demonstrate spatially resolved imaging, enabling us to study dipolar energy transport. To reach single impurity sensitivity we investigate our current detection fidelity and characterize the signal and noise contributions in IEI. We model our interacting system, finding good agreement with experimental data. Based on this model, we predict combinations of Rydberg states for which single-shot single impurity sensitivity should be possible in future experiments.