Transport of a single cold ion immersed in a Bose-Einstein condensate

TL;DR

This paper explores the diffusive transport and cold chemistry of a single ion in a Bose-Einstein condensate, revealing insights into impurity mobility and inelastic molecular processes in ultracold quantum gases.

Contribution

It introduces a method to study single ion transport and cold chemical reactions within a BEC, providing new understanding of impurity dynamics and inelastic collisions at ultracold temperatures.

Findings

Impurity exhibits diffusive transport in the BEC.

Measured ion mobility through stochastic simulations.

Observed inelastic molecular-ion formation and rovibrational quenching.

Abstract

We investigate transport dynamics of a single low-energy ionic impurity in a Bose-Einstein condensate. The impurity is implanted into the condensate starting from a single Rydberg excitation, which is ionized by a sequence of fast electric field pulses aiming to minimize the ion's initial kinetic energy. Using a small electric bias field, we study the subsequent collisional dynamics of the impurity subject to an external force. The fast ion-atom collision rate, stemming from the dense degenerate host gas and the large ion-atom scattering cross section, allows us to study a regime of frequent collisions of the impurity within only tens of microseconds. Comparison of our measurements with stochastic trajectory simulations based on sequential Langevin collisions indicate diffusive transport properties of the impurity and allows us to measure its mobility. Furthermore, working with a free and untrapped ion provides unique means to distinguish single realizations, where the impurity is subject to inelastic molecular-ion formation via three-body recombination. We study the cold chemistry of these events and find evidence for subsequent rovibrational quenching collisions of the produced molecule. Our results open a novel path to study dynamics of charged quantum impurities in ultracold matter.