Dynamics of Single Neutral Atoms Coupled to Baths

Artur Widera

Experimental advances in controlling and probing single neutral atoms has proven valuable to explore quantum phenomena with unprecedented resolution. We employ such control to investigate dynamics of single atoms in engineered baths to study fundamental statistical physics and diffusion dynamics on a single particle level. First, we observe nonergodic diffusion of single Cesium atoms trapped in a periodic potential and coupled to a near-resonant light field. Our findings may be relevant for the interpretation of various observations in, e.g., life science experiments. Second, we observe the diffusion of single Cesium "tracer" atoms impinging on an ultracold cloud of Rubidium. We observe the effect of individual collisions, which form the most fundamental building block of diffusion. In our case, the gas is dilute and the mass ratio of tracer and gas atoms is close to unity, revealing the discrete nature of the bath. However, we are able to model the dynamics over a broad range of densities with a continuous medium type Langevin equation, where friction and fluctuation terms become velocity dependent. We find excellent agreement without free parameters, extending the validity range of the highly successful continuous diffusion description into a new regime.