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

Atoms are then optically pumped to the |F = 2,mF = 2〉 state. A weak uniform
magnetic field (B ≈ 1 G) is turned on during the optical pumping time (≈ 100 µs)
to define a quantization axis. Approximately 73% of the atoms are transferred to the
|F = 2,mF = 2〉 state, while the other atoms remain in the |F = 2,mF = 1〉 state.
All beams are then turned off and shuttered, and the magnetic field gradients
are increased to 48 G/cm within a few ms, confining the atoms in the magnetic trap.
To decrease the thermal equilibration time, the magnetic field gradients are increased
to 96 G/cm in about 200 ms, increasing the collision rate. After about 5 seconds the
atoms reach thermal equilibrium and the gradients are reduced to 72 G/cm. At this
point about 10 7 Rb atoms at a temperature of 50 µK are confined in the magnetic trap.
Controlling the temperature of the atoms in the magnetic trap is important for the
study of single-photon cooling. By varying the detuning in the MOT beams during the
loading and optical molasses phases, the temperature can be varied between about 30
and 55 µK.
Using standard laser cooling techniques is, however, not required to load atoms
into a magnetic trap. It has been shown that it is feasible to decelerate a supersonic
beam of atoms using an atomic coilgun [77–79]. At low velocities these atoms can then
be directly loaded into a magnetic trap.
h
demon beam
Figure 5.1: Alignment of the demon beam inside the optical trough.
Once the rubidium atoms are transferred into the magnetic trap, the optical
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