Coherence and Collisions in Ultracold RbCs Molecules

Abstract

This thesis presents work towards the development of a quantum simulator based on RbCs molecules using a bulk sample of up to ~4000 molecules at temperatures of ~1 µK.

We demonstrate coherent control over the molecules' internal state using resonant microwave fields. We test this coherence by performing high resolution Ramsey spectroscopy of the first rotational transition and observing how the contrast of the spectroscopic fringes decay. We are able to affect the coherence of the superposition using an external laser field, as the two component states have a significant differential AC Stark shift. We extend this microwave control by including an additional microwave field, demonstrating the Autler-Townes effect with hyperfine state resolution and transfer between two hyperfine states in .

We study the internal structure of the molecule in the presence of external fields focussing on controlling the differential AC Stark shift between the rotational ground state and the first excited state. We investigate the effect of the off-resonant light on the internal structure in static magnetic and electric fields. In the DC electric field we use two models to describe the molecular structure, demonstrating that at modest values of the electric field the nuclear spin angular momentum is decoupled from the rotational angular momentum of the molecule, this enables us to construct a set of optimum trapping parameters for states with .

Through careful measurements of the molecular lifetime we are able to determine that molecular losses are limited by two-body collisions. By introducing a time dependent intensity modulation to our optical trap we are further able to determine that the dominant loss process in bulk samples of ultracold RbCs molecules is the laser excitation of collision complexes.

Finally, we investigate the collisional properties of RbCs with Rb and Cs atoms. We find that the loss is caused by single molecule-single atom collisions and sub-universal over a wide range of magnetic fields.