Towards a novel platform for imaging molecules in an optical lattice

Abstract

This thesis reports on the development of a new apparatus which will be used to produce rovibrational ground state molecules with the goal of imaging them in an optical lattice. These types of experiments are often referred to as quantum gas microscopes.

The two molecules which we wish to study are RbCs and KCs. RbCs has been already studied substantially at Durham but not in an apparatus as advanced as the one discussed in this thesis. RbCs and other ground state diatomic molecules may be formed in the rovibrational ground state by us-
ing a magnetoassociation on an interspecies Feshbach resonance followed by stimulated Raman adiabatic passage (STIRAP). In our new apparatus we plan to repeat this in an optical lattice positioned directly above an object-
ive with a high numerical aperture which will have the capability to resolve single lattice sites. Loading molecules into an optical lattice will allow access
to dipolar physics associated with the intrinsic electric dipole moment of the molecule. This will grant us the capability to perform experiments, such as quantum simulation, that can yield a deeper understanding of the quantum nature of matter confined in lattices. In addition we show work towards KCs molecules, of which ground state molecules are yet to be formed. This molecule has a dipole moment of 1.92 D and a stable fermionic isotope which
makes it a promising candidate for our studies in addition to RbCs.

A new vacuum chamber apparatus is constructed. A pair of 2-dimensional magneto-optical traps (2D-MOTs), one for Cs and the other for K/Rb, provides a flux of atoms to the centre of our main vacuum chamber. Here the atoms are collected in a 3D-MOT. The 3D-MOT can accumulate 108 Cs atoms, 109 Rb atoms and 108 K atoms. The laser setups for our MOTs are
also presented in this thesis. We laser cool Rb, Cs and K on their respective D2 transitions. There is a particular focus on the optimisation process of K. We have managed to cool a sample of 108 K atoms to 42(2) μK and obtain a simultaneous MOT of both K and Cs. We have potential plans to further cool K on the D1 line. To achieve this we need some means of high quality frequency stabilisation so a study on the modulation transfer spectroscopy of K and a comparison against the associated theory is also presented in this thesis.

Using a moving optical standing wave the atoms are transported to the science cell. They will subsequently undergo various cooling stages until the phase space density is sufficiently high for magnetoassociation. This has been achieved with Rb and Cs but not yet for K and Cs. They will then be loaded into an optical lattice and associated into molecules.

STIRAP requires lasers frequency stabilised to less than a kHz. The STIRAP setup is also described in detail in this thesis. We lock two lasers of wavelength 895 nm and 1359 nm to an ultra low expansion cavity and demonstrate proof of concept of how such a setup can serve the dual purpose of both STIRAP for KCs molecules and for exciting Cs atoms to Rydberg states using the Cs D1 transition.