Towards Zeeman-Sisyphus Deceleration of CaF Molecules

Abstract

Molecular beams have been fundamental in furthering our understanding of many aspects of physics and chemistry. This progress is set to continue, as attention turns to producing slow and controllable beams, for applications ranging from high precision studies of chemical reactions to quantum simulation of complex condensed matter systems. However, the complexity that makes molecules such an attractive platform for these applications leads to challenges when experimentally producing such slow beams.

A variety of deceleration techniques have been developed to address these challenges. Zeeman-Sisyphus deceleration is one such technique, which promises to be highly versatile and applicable to a large variety of molecular species, including heavy molecules or those with unfavourable
branching ratios. The decelerator consists of alternating high and low static magnetic field regions. Optical pumping is employed to ensure that the molecules propagating through the decelerator continually climb up the generated potential hills, and thus lose kinetic energy in the process.

In this thesis I describe the construction of a new molecular experiment at Durham University and the progress made towards testing Zeeman-Sisyphus deceleration of calcium monofluoride (CaF) molecules. First, we present simulations of the proposed deceleration scheme. A reduction in average forward velocity from 130 to 63 m/s is demonstrated, which corresponds to an expected ∼ 105 molecules arriving within a typical magneto-optical trapping (MOT) region, with velocities below the MOT capture velocity.
Secondly, I discuss the experimental progress. A cryogenic buffer gas source is constructed,capable of producing pulses of CaF molecules with an average forward velocity ∼130 m/s. For effective optical pumping within the decelerator, two beams with a frequency separation of 19 GHz are required. The characterisation of the high-frequency EOM and filtering etalons used to achieve this is discussed, alongside the possible effects of additional frequencies on the efficiency of the optical scheme. Additionally, an all-digital scanning transfer cavity locking system is implemented. This cost-effective system is flexible and highly scalable, as multiple follower lasers, with wavelength differences on the order of 100s of nm, can be locked simultaneously.

The work described in this thesis provides a solid foundation for the future of the experiment. In the short term this will include a full characterisation of the Zeeman-Sisyphus deceleration of CaF molecules, and later, the development of a quantum simulation platform with optically trapped CaF.