A Single Ion in an Ultracold Neutral Bath: Coordination, Snowballs and Polaronic Effects

In this work, we study the ground state properties of a single ¹⁷⁴Yb⁺ ion immersed in an ultracold gas of ⁷Li atoms. Our main technique is the quantum diffusion Monte Carlo (DMC) algorithm. We use basin-hopping, a classical potential function optimization algorithm, to choose the initial positions of the particles in DMC. By using longest-processing-time-first parallelization to run DMC several times with several different parameters, we explore the effect of the atom-ion potential depth and short-range equilibrium distance on the number, arrangement, and density of the number of particles which minimizes the average energy per particle. To ensure the reliability of our results, we use a large number of timesteps, and check for convergence with respect to the number of replicas and step size. After considering the case when the bath of neutral atoms is either a liquid or a quantum gas, and also the impact of trapping the ion with electric fields, we conclude that the atom-ion short range physics has a huge impact on the ground-state properties of this system and exotic many-body physics effects, such as polarons.