NSF Award
1607377
The goals of this project are twofold: first, to understand and control the movement of energy among strongly connected groups of atoms, and second, to improve an experimental technique for measuring the energy distribution among these atoms. These general goals are present in many areas of science (for example, in the study of the transport of energy in metals) but they are often difficult to realize for the simple reason that solids are densely packed with atoms and typically opaque. This work will be done in an "ultracold gas" of atoms that are cooled so that they move slowly like the atoms in a solid, but are at low density. Collections of these atoms are transparent and can be probed and controlled with lasers. If the outer electrons in these atoms are excited to high energy levels, then the atoms can exchange energy in ways that are similar to other quantum systems. Using a combination of simulation and experimental imaging techniques, the transport of energy will be measured. In this way, the project aims to create and study atomic systems that will yield insight into both fundamental quantum mechanics and the behavior of materials. The second goal of this project concerns a widely used experimental technique in which the energy level of an electron is measured by using a rapidly increasing electric field to rip off, or ionize, the outermost electron from the atom. The stripped electron is accelerated to a detector and the resulting signal is characteristic of the electron's original energy level. However, the ionization process is complex and nearby energy levels produce signals which are indistinguishable. This project will precisely shape the electric field pulse so that the signals from closely spaced energy levels can be distinguished, making new experiments possible in many areas of atomic physics.<br/><br/>In this project, the valence electron of ultracold rubidium atoms in a magneto-optical trap is excited to a weakly bound state of high principle quantum number, or Rydberg state. Both the spatial distribution of the atoms and the internal states to which they are excited are precisely controlled. The atoms in such a sample exchange energy through a dipole-dipole interaction. Building upon earlier work implementing "state selective field ionization" with two parallel cylinders of atoms excited to two different Rydberg states, other geometries and state distributions will be explored. As the electron's amplitude traverses the many avoided crossings on the way to ionization it splits due to Landau-Zener transitions and spreads throughout many Stark levels, complicating the identification of the original electronic energy level. Previous attempts at manipulating the electron's path to ionization have focused on coarsely determining the slope of the electric field ramp. Since there are hundreds of avoided crossings on the way to ionization, a genetic algorithm will be used to design the electric field ramp. In addition, recent simulations have revealed the possibility of observing the anisotropic nature of the dipole-dipole interaction as well as Anderson localization.
