Control and Collisions of 87Rb and 133Cs Atoms in Optical Tweezers

Abstract

This thesis reports the first steps towards the production of an optical tweezer array of ultracold 87Rb133Cs molecules. Such a system represents a longstanding goal: the full quantum control of individual polar molecules. Harnessing the long-range dipolar interactions and the rich rovibrational structure of ultracold molecules will unlock new applications in quantum computation, quantum simulation and quantum chemistry.

We demonstrate loading of single Rb and Cs atoms into species-selective optical tweezers of wavelengths 814 nm and 938 nm from magneto-optical traps of each species. We characterise the tweezers, detailing measurements of the trap frequency, light shift, trap waist and mean atom temperature. These measurements are performed using a newly-built apparatus, the design and construction of which are described in depth.

Next, we demonstrate control of the internal state of the atoms through optical pumping and microwave transfer. Using an acousto-optic deflector, we demonstrate control of the tweezer position, which is used to produce and rearrange a 1D array of five Cs atoms. Furthermore, we use this positional control to merge species-selective tweezers, which is used to prepare exactly one Rb atom and one Cs atom in the same optical tweezer.

We then use our control of individual atoms to study interatomic collisions. We demonstrate transfer of two or three Cs atoms into the same optical tweezer without heating, and discuss a method of separating tweezers to image multiple homonuclear atoms. We perform Feshbach resonance spectroscopy using pairs of Cs atoms prepared in the same optical tweezer. We observe nine loss features corresponding to Cs Feshbach resonances, and one loss feature corresponding to a zero in the scattering length. Finally, we study interspecies collisions of one Rb atom and one Cs atom.

The next steps towards an array of ground-state polar molecules, namely magnetoassociation and stimulated Raman adiabatic passage, will build on the work presented here.