Copyright by Kirsten Viering 2006 - Raizen Lab - The University of ...

In all the calculations done above we have assumed the Raman detuning δ to be
zero, i.e. the difference frequency equals the hyperfine splitting of the Sodium ground
states in absence of a magnetic field (1.772GHz). By changing the detuning we can vary
the position of the resonant Raman region in space. A detuning of 1MHz corresponds
to a spatial shift of the resonant region by 7.55 µm.
6.5 Experimental procedure to determine the transfer efficiency
of stimulated Raman transitions
The experimental procedure used to test the efficiency of the Raman pulse is rather
simple. After loading the MOT and cooling the trapped atoms, the repump beam is
turned off. Therefore atoms that fall into the |F = 1〉 state remain there and are separated
from the |F = 2〉 → |F ′ = 3〉 cycling transition. Eventually all atoms will fall into this
dark state. The atoms can then be transferred into the magnetic trap. In the future,
the trap will be in an Anti-Helmholtz configuration with an optical plug [31]. In this
trap only the atoms with the magnetic sublevel M=-1 will be trapped. An evaporation
cooling technique is then used to create a Bose Einstein Condensate. The optical lattice
is created next and the atoms are confined to individual lattice sites.
A Raman pulse is then applied and the corresponding number of atoms make
the transition to the |F = 2〉 state. The resonant light is turned on. Although the resonant
light forms a closed transition all atoms will eventually fall in the |F = 1〉 state again
after a certain number of cycling transitions. During this process they gain energy and a
time-of-flight measurement could separate the two atom groups and the atom number
of those that made the Raman transition can be determined. Knowledge of the initial
number of atoms is a crucial element of determining the Raman transition efficiency.
One therefore must be certain that the initial number of atoms does not vary by more
than a few percent.
Knowing the ideal pulse duration one can study the population transfer effi-
ciency as a function of a magnetic bias field. The relation between those two can then be
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