Cooling and heating of atoms colliding in an optical field

S. Nußmann

Ana Rakonjac

This thesis describes the construction of a dual species setup using fermionic 40K and bosonic 87Rb with the goal of cooling to ultracold temperatures and quantum degeneracy, and also perfoming precision collision experiments using a novel optical collider. The setup is composed of a dual species magneto-optical trap, with transfer to an ultrahigh vacuum science cell achieved using a mechanical transport scheme. Atoms are cooled to ultracold temperatures using forced radio frequency evaporation in a Ioffe-Pritchard style magnetic trap. The optical collider utilises the optical dipole force to trap a sample of ultracold atoms and accelerate them towards a target sample using an acousto-optic modulator. The process of cooling 87Rb atoms in the |F = 2, mF = 2> hyperfine state to Bose-Einstein condensation is described, as well as progress towards production of ultracold 40K. Design, implementation, and characterisation of the optical collider is provided, showing that it is a precision metrology device.

M. Ia. Amusia, A. S. Baltenkov

A Aghajani-Talesh, M Falkenau, Valentin Volchkov +3 more

We report on the transverse laser cooling of a magnetically guided beam of ultracold chromium atoms. Radial compression by a tapering of the guide is employed to adiabatically heat the beam. Inside the tapered section, heat is extracted from the atom beam by a two-dimensional (2D) optical molasses perpendicular to it, resulting in a significant increase in atomic phase space density. A magnetic offset field is applied to prevent optical pumping to untrapped states. Our results demonstrate that, by a suitable choice of the magnetic offset field, the cooling beam intensity and detuning, atom losses and longitudinal heating can be avoided. Final temperatures below 65 μK have been achieved, corresponding to an increase in phase space density in the guided beam by more than a factor of 30.

A. M. Bonch-Bruevich, Sergey G. Przhibel'skii, V. V. Khromov

Bimalendu Deb

In contrast to atomic cooling achieved through laser techniques, molecular cooling generally involves not only cooling translational motion but also vibrational and rotational motion. Cooling molecules directly using the laser cooling method is an extremely difficult or even impossible-seeming task in most cases at present. An alternative approach is to associate two colliding cold atoms to form a molecule that is translationally and rotationally cold. The method by which two cold atoms bind together into a molecule in the presence of external fields is called ‘association spectroscopy,’ which is an inelastic collision process afforded by an external field. There are three kinds of association spectroscopy: (1) photoassociation (PA), (2) magnetoassociation, and (3) magneto-optical association. We briefly discussed PA in the previous chapter. This type of spectroscopy is a result of advancements in the field-assisted collision physics of cold atoms. In this chapter, we provide a description of these three types of association spectroscopy.