Experiments to Control Atom Number and Phase-Space Density in ...

Chapter 8
Towards Fock States of Lithium Atoms
Even though the lithium experiment has not been able to create Fock states yet,
significant progress towards this goal has been made. This chapter summarizes this
progress, showing data on MOT properties, CO2 laser alignment, dipole trap loading
and initial signs of evaporative cooling.
8.1 MOT Properties
The lithium oven typically operates at a temperature of 350 ◦ C. At this temper-
ature about 1.5×10 8 atoms/second are loaded into the MOT. If everything is aligned
optimally this number is frequently exceeded. Figure 8.1 shows the MOT loading. The
MOT is loaded for a time t before the MOT and Zeeman slower light are turned off.
Fluorescence imaging then determines the atom number. The MOT typically saturates
around5×10 8 atoms, at optimum alignment the saturation value can be higher. Loading
rates up to3×10 8 atoms and saturation values of up to1×10 9 atoms have been achieved.
At a higher oven temperature the MOT loads faster, however, the lithium reservoir will
be depleted faster and the current loading rate is sufficient for the experiment.
The lifetime of the magneto-optically trapped atoms can be used as a direct
measure to determine the collision rate with background atoms. In a MOT there are
two processes that can lead to traploss. At high atomic densities, the loss is dominated by
two-body loss, which occurs when two trapped atoms collide with each other. At lower
densities, two-body collisions are reduced and collisions with atoms from the background
gas are the dominating loss mechanism. The lifetime of the MOT in the low density
limit is thus a good indication of the background pressure and how this pressure will
limit the lifetime in the optical dipole trap.
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