This dissertation details an experimental investigation of the center-of-mass motion of cesium atoms in a time-dependent lattice of light. The research described here proceeds along two general lines. The first group of experiments considers a realization of the quantum kicked rotor, where the optical lattice is applied in a series of short, periodic pulses. In the regime where the classical description of this system is strongly chaotic, the quantum and classical dynamics differ remarkably due to dynamical localization, which is a manifestation of the quantum suppression of classical chaos. Because this quantum localization is a coherent effect, it should be vulnerable to noise or coupling to the environment, providing a mechanism for restoring classical behavior at the macroscopic level. The experimental results confirm that dynamical localization can be destroyed by adding noise and dissipation in a controlled way, and furthermore they show that quantitative agreement between the experiment and a classical model can be reached with a sufficient level of applied noise.
The second line of research considers the weakly chaotic regime, where stable and chaotic regions coexist in phase space. The optical lattice is modulated sinusoidally in these experiments to realize the amplitude-modulated pendulum. Careful preparation of the initial atomic state, including stimulated Raman velocity selection, is necessary to resolve the phase-space features. Coherent tunneling oscillations are observed between two symmetry-related islands of stability in phase space. Because the classical transport between the islands is forbidden by the system dynamics, as opposed to a potential barrier, the tunneling in this experiment is an example of dynamical tunneling. Additionally, the experimental data indicate through multiple signatures that the tunneling is enhanced by the presence of the chaotic region in phase space, an effect known as chaos-assisted tunneling.