Dynamics of a ground-state cooled ion colliding with ultra-cold atoms

TL;DR

This study investigates the energy dynamics of a ground-state cooled ion colliding with ultra-cold atoms, revealing a non-Maxwellian energy distribution influenced by trap dynamics and collision forces.

Contribution

It demonstrates that the interaction energy scale is set by collision forces and trap effects, not temperature, highlighting intrinsic limits in ion-atom systems.

Findings

Energy distribution deviates from Maxwell-Boltzmann to Tsallis

Interaction energy is determined by collision force and trap dynamics

Quantum effects can be studied at the first collision despite overall heating

Abstract

Ultra-cold atom-ion mixtures are gaining increasing interest due to their potential applications in quantum chemistry, quantum computing and many-body physics. Here, we studied the dynamics of a single ground-state cooled ion during few, to many, Langevin (spiraling) collisions with ultra-cold atoms. We measured the ion's energy distribution and observed a clear deviation from Maxwell-Boltzmann to a Tsallis characterized by a power-law tail of high energies. Unlike previous experiments, the energy scale of atom-ion interactions is not determined by either the atomic cloud temperature or the ion's trap residual excess-micromotion energy. Instead, it is determined by the force the atom exerts on the ion during a collision which is then amplified by the trap dynamics. This effect is intrinsic to ion Paul traps and sets the lower bound of atom-ion steady-state interaction energy in these systems. Despite the fact that our system is eventually driven out of the ultra-cold regime, we are capable of studying quantum effects by limiting the interaction to the first collision.