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Transcript
Chapter 5. Experimental Apparatus II
160
5.1
Overview
In this chapter we discuss several modifications to the experimental apparatus described in
Chapter 3. These improvements were necessary to prepare localized atomic wave packets in
phase space for the experiments in Chapter 6. The first step towards such localized initial
states is further cooling of the atoms beyond what is possible in a typical MOT. We accomplished this additional cooling in a three-dimensional, far-detuned optical lattice, as we discuss
in Section 5.2. Further velocity selection well below the recoil limit was accomplished using
two-photon, stimulated Raman transitions. We will examine the theory of stimulated Raman
transitions as well as their experimental implementation in Section 5.3. It was also necessary
to have control over the spatial phase of the optical lattice, so that the wave packet could be
shifted to various initial locations in phase space. This spatial control was accomplished through
an electro-optic phase modulator placed before the standing-wave retroreflector, as described
in Section 5.4. Finally, we trace through the entire state-preparation sequence, using all these
atom-optics tools, in Section 5.5, and we discuss the calibration of the optical-lattice potential
in the modified setup in Section 5.6.
5.2
Cooling in a Three-Dimensional Optical Lattice
Using the standard techniques of cooling and trapping in a MOT, as described in Chapter 3, we
were limited to temperatures on the order of 10 µK for the initial conditions of the experiment.
It is desirable, however, to have much lower temperatures for the initial conditions, especially
looking towards experiments with minimum-uncertainty wave packets in phase space. Although
it has been shown that temperatures below 3 µK can be achieved in cesium using a standard
six-beam MOT [Salomon90], our MOT temperatures were substantially higher due to residual
magnetic fields from eddy currents in the stainless steel vacuum chamber after the field coils
were switched off. One successful approach to achieving additional cooling beyond that of a
standard MOT is cooling in a three-dimensional optical lattice. Several methods for cooling in
three-dimensional optical lattices have been demonstrated [Kastberg95; Hamann98; Vuletić98;
Kerman00], but the method implemented here was based on the setup developed by the group