The force of light: from tweezing bacteria to ultracold interactions between ions, atoms and molecules

*Abstract*:

Since optical traps have been proposed in 1970 by Ashkin, they have undergone an impressive evolution. This remarkably versatile instrument was successfully used across several disciplines to trap and manipulate particles ranging from individual bacteria, viruses and micron-sized glass spheres to ultracold atomic ensembles. Modern optical dipole traps have reached a point where minute control on the level of individual atoms is possible with an extensive degree of control.

This kind of individual addressability is one of the outstanding feature of another profoundly influential invention: radiofrequency (RF) traps for atomic ions. These systems offer a unique level of control accompanied by, e.g., long coherence times, excellent state preparation and readout efficiencies and record-worthy qubit gate fidelities. However, in some applications, most notably in investigations of ultracold ion-neutral interactions, the presence of RF fields leads to detrimental effects imposing severe restrictions on the accessible collision energies.

I will discuss a new experimental approach to studying ion-neutral interactions aiming to combine several key features of ions, foremost their long-range Coulomb interaction, with the versatility of optical traps. This technique known as optical ion trapping allows for confining single ions or ion Coulomb crystals without RF fields and offers comparatively long lifetimes on the order of seconds. I will present recent results demonstrating sympathetic cooling of an ion immersed into an ensemble of ultracold atoms overlapped in a set of optical dipole traps, and discuss their potential applications in several fields ranging from quantum chemistry to novel quantum simulations. Lastly, I will discuss how the most recent achievements in the fields of neutral molecular quantum gases and ion-atom collisions can be combined to enable an entirely new class of hybrid ion-molecule interaction experiments in the ultracold regime.