An experiment apparatus for the production of ultracold bosonic dipolar ground state 23Na39K molecules and Feshbach spectroscopy in a cold mixture of 23Na and 39K

Abstract

The field of ultracold matter has developed rapidly over the course of the past twenty to thirty years. One outstanding achievement has been the realisation of Bose-Einstein condensation (BEC) only 23 years ago. Many other fascinating observations of quantum phenomena have been made at an incredibly fast pace using ultracold atomic samples with contact force interactions as a testbed. Due to the rapid successes of all these experiments on atomic ensembles, researchers began to aim for more elaborate inter-particle interactions.

A possible additional one is the dipole-dipole interaction (DDI), the long-range character of which stands out in comparison to the contact interactions. Moreover, DDI is anisotropic and the possibility to tune the direction of the dipoles in the experiment as well as the interaction strength promises the possibility to study a plethora of new quantum phenomena.

In recent years, several experiments using different combinations of alkali atoms to create ground-state hetero-nuclear molecules in the ultracold regime have been set up, following the pioneering work on KRb molecules. Of all possible combinations of two alkali atoms, NaK combines the advantages of a high induced electric dipole moment of 2.72 Debye, chemical stability of the ground-state molecules, the possibility to realise bosonic as well as fermionic molecules and a large knowledge base for cooling and trapping of the two atomic species.

This thesis reports on the development and construction of an experiment apparatus for the production of ultracold bosonic dipolar ground state 23Na39K molecules. This includes the setup of an ultra-high vacuum (UHV) system, several laser light sources, microwave (MW) and radio frequency (RF) antennas and electronics to control the various components of the experiment. The system pre-cools the atomic samples of 23Na and 39K and loads them into a dual-species three-dimensional magneto-optical trap (3D MOT). After a transfer to a magnetic quadrupole trap, the mixture is cooled by forced MW evaporation until three-body losses limit dual-species operation at high densities and zero magnetic field. Using the pure optical trapping potential of a crossed optical dipole trap (cODT) and RF- state-transfer, the scattering properties of the bosonic mixture of 23Na+39K are investigated in extensive atom loss measurements for a magnetic field range from 0 to 750 G. Several Feshbach resonances, zero crossings of the interspecies scattering length and inelastic loss features in many different scattering channels are identified. The results of this study are used to refine the molecular potentials of NaK and to produce a dual-species quantum-degenerate mixture of two BECs in the state (f = 1, mf = −1) of 23Na + (f = 1, mf = −1) of 39K. The measurements and refined molecular potentials will considerably aid in the future realisation of 23Na39K molecules in their absolute ground state.