Daniel A. Steck

Ballistic peaks at quantum resonance

We report studies of the motion of cold atoms in a time-dependent optical potential. The dynamics of our system are that of the quantum kicked rotor, and exhibit a wide variety of phenomena. One purely quantum effect is the quantum resonance, which occurs for well-chosen initial conditions and specific values of the period between kicks. Distinctly nonclassical behavior, such as ballistic growth in momentum, is possible at a quantum resonance. Previous experimental studies have observed these resonances, but have not clearly resolved the expected ballistic motion. We now observe ballistic motion at quantum resonances and compare our momentum distributions with theory and numerical simulations.

Quantum chaos with cesium atoms: pushing the boundaries

Atomic motion in pulsed, periodic optical potentials provides a unique experimental testing ground for quantum chaos. In the first generation of experiments with sodium atoms we observed dynamical localization, a quantum suppression of chaotic diffusion. To go beyond this work we have constructed an experiment with cold cesium atoms, and report our first results from this system. The larger mass and longer wavelength push out the momentum boundary in phase space that arises from the nonzero duration of the pulses. This feature should enable the study of noise effects and dimensionality on dynamical localization. We propose a new method of quantum state preparation based on stimulated Raman transitions for studies of mixed phase space dynamics. c 1999 Elsevier Science B.V. All rights reserved.

Timing noise effects on dynamical localization

The quantum kicked rotor is studied experimentally in an atom-optics setting, where we observe the center-of-mass motion of cold cesium atoms. Dynamical localization in this system typically suppresses classical diffusive motion, but is susceptible to the addition of various forms of noise. We study in detail the effects of timing noise, where variations are introduced to the times at which the kicks occur. This noise is particularly interesting because it does not directly induce momentum diffusion. However, it is found that the addition of timing noise efficiently destroys both the classical correlations that give rise to fluctuations in the classical diffusion rate as well as quantum coherences that lead to dynamical localization.

Experimental study of quantum chaos with cesium atoms

To go beyond the first generation of quantum-chaos experiments, we set up an experiment with cesium. The small recoil velocity of cesium relative to sodium ensures that the 6-kicked approximation is valid over a much larger range of momenta. The resulting momentum boundary in phase space is then pushed out much further, opening the door for experimental studies of noise-induced delocalization as well as other directions of fundamental interest. Cesium atoms are first trapped and cooled in a magneto-optical trap (MOT) via diode lasers.