Towards Quantum gas microscope for 87Rb133Cs molecules

Abstract

This thesis reports on a new apparatus for a quantum gas microscope for
ultracold molecules to study dipolar physics in lattices. The setup is capable of creating two species of quantum degenerate bi-alkali molecules in the
absolute ground state: 87RbCs and KCs.

We describe the setup of vacuum chambers, magnetic coils and laser systems to produce Bose-Einstein condensates (BEC) of Cs and Rb. We start with an optimisation of the Cs BEC. A cold sample is prepared with a two-dimensional magneto-optical trap (2D-MOT+) which is then loaded to form a three-dimensional MOT (3D-MOT) in a separated main chamber. Next, we compress the 3D-MOT to increase the density and further cool and polarise atoms using 3D degenerate Raman sideband cooling (dRSC). Then, to increase the phase-space density (PSD) to reach quantum degeneracy we employ evaporative cooling by loading the atomic cloud into a a large volume dipole trap (reservoir trap) followed by a tighter dipole trap (dimple trap).

Then, we demonstrate the laser system that combines two wavelengths for Cs
and Rb Raman lattice on one optical fiber for each path of the lattice light.
The Rb lattice light is generated using an injection locking technique to
yield adequate power. We investigate two methods to stabilise the laser
frequency which are digital beat locking using an optical phase-lock loop and
off-resonance frequency locking using the Faraday effect. The latter method is
ultimately implemented because it has the potential to stabilise the frequency
far from the transition up to 19 GHz.

Finally, we utilise the Cs BEC to perform a measurement of the tune-out wavelength at 880 nm. We measure the polarisability as a function of
wavelength using Kapitza-Dirac scattering of the Cs BEC exposed by a pulse
of a one-dimensional optical lattice.

The next steps to make the lowest vibrational ground-state molecules will
carry on from the work presented in this thesis. Those are optical transport
of the two-species atomic clouds from the main chamber to the science cell,
magnetoassociation and stimulated Raman adiabatic passage.