Collaborative Research: Cold Rydberg Atoms

这个项目的目标有两个：第一，理解和控制强连接原子群之间的能量运动，第二，改进测量这些原子之间能量分布的实验技术。这些总体目标存在于许多科学领域（例如，研究金属中的能量传输），但它们往往难以实现，原因很简单，即固体被原子密集地包裹着，通常不透明。这项工作将在原子的“超冷气体”中进行，这些原子被冷却，使它们像固体中的原子一样缓慢移动，但密度很低。这些原子的集合是透明的，可以用激光探测和控制。如果这些原子的外层电子被激发到高能级，那么原子就可以以类似于其他量子系统的方式交换能量。利用模拟和实验成像技术的结合，能量的传输将被测量。通过这种方式，该项目旨在创建和研究原子系统，从而深入了解基本量子力学和材料行为。该项目的第二个目标涉及一种广泛使用的实验技术，该技术通过使用快速增加的电场从原子中剥离或电离最外层的电子来测量电子的能级。被剥离的电子被加速到检测器，产生的信号具有电子原始能级的特征。然而，电离过程是复杂的，附近的能级产生的信号是难以区分的。这个项目将精确地塑造电场脉冲，以便能够区分来自间隔很近的能级的信号，从而使原子物理学的许多领域的新实验成为可能。在这个项目中，超冷铷原子的价电子在磁光阱中被激发到一个高主量子数的弱束缚态，即里德伯态。原子的空间分布和它们被激发到的内部状态都是精确控制的。这种样品中的原子通过偶极-偶极相互作用交换能量。在早期工作的基础上，将两个平行的圆柱体原子激发到两个不同的里德伯态，实现“状态选择场电离”，其他几何形状和状态分布将被探索。当电子的振幅在电离过程中穿过许多避免的交叉点时，由于朗道-齐纳跃迁而分裂，并在许多斯塔克能级上扩散，使原始电子能级的识别复杂化。先前操纵电子电离路径的尝试主要集中在粗略地确定电场斜坡的斜率。由于在通往电离的路上有数百个避过的交叉点，因此将使用遗传算法来设计电场坡道。此外，最近的模拟揭示了观察到偶极-偶极相互作用的各向异性性质以及安德森局域化的可能性。

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.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.