The combination of magnetic and optical forces cools and traps the atoms. I used another laser beam to further trap the atoms, though it raises the temperature to about 240 microkelvin. In the FORT, I study cold collisions of Rubidium by means of photoassociation. Photoassociation is the creation of a bound diatomic molecule by absorbtion of a photon. In particular, I look at long range molecular states, where the mean separation of the atoms is 10 to 40 Angstroms.
Typical molecules have atomic separations of just a few Angstroms.
This new, excited molecule is perhaps the most basic molecule, existing for just a short time before the atoms fly apart. Examining these molecules at very low temperatures is the key to isolating molecular states unobservable in warmer environments. When investigating photoassociation, I examine the rotational and vibrational energy spectra of the excited molecule. The ground state potential has a small centrifugal barrier at certain rovibrational levels through which the atoms must tunnel before they bond. Currently I'm looking at the time dependence of this transition in order to determine the tunneling rate through the barrier.