Scattering by Strong Long-Range Forces, Quantum Superposition States of Nanoscale Objects: Exploring Quantum Rrocesses with the Use of Atomic Clusters

本研究项目利用质量选择原子纳米团簇束流的实验技术和能力，研究了两类既具有基本性质又具有重要现实意义的量子现象。第一个主题涉及长程势“大永久偶极子的势”对非弹性碰撞的影响。具体地说，将首次测量电子被非常强的电偶极场俘获的绝对截面。此外，还将探索迄今为止尚未探索的巨型磁偶极子对俘获过程的影响。原子团簇代表了这种测量的唯一合适的目标。该项目的第二部分将确定一种存在于纳米尺度上的新型量子共振：一种处于与两个几何形状的量子线性叠加相对应的状态的团簇粒子。这种鉴定将通过对具有明确尺寸和同位素组成的自由金属团簇的激光光谱分析来完成。具有电子壳层结构的尺寸选定的金属团簇的光学光谱(也称为“人造原子”)将被用来检测其同位素质量对集体电子共振吸收的影响。这种特殊的同位素效应将揭示纳米尺度领域中一种新的量子共振现象：原子团簇形状构型的量子叠加。原子团簇是由有限数量的原子组成的纳米级聚集体，从几个原子到数千个原子。它们的一端是单个原子和分子之间的桥梁，另一端是较大的粒子(如微结构和气雾剂)和大宗材料之间的桥梁。精确调整星团大小和组成的能力使人们能够准备具有有用和不寻常特征的量子大小的物体，并研究与这些特征相关的新的物理现象。在这个项目中使用的一个特性是，某些星系团能够在其附近产生极强的电场和磁场，并利用这些磁场来吸引和捕获附近的带电粒子，例如电子。该项目将测量这一过程的效率，到目前为止，该过程从未探索过像“极地”星系团产生的场强这么高的场强。除了提供新的基本见解外，这些结果还将对理解超冷分子和离子的相互作用、实现通过外部磁场控制化学反应的目标、研究磁性纳米颗粒以及了解大气和星际环境中发生的过程具有实际意义。在该项目的第二部分，将研究纳米团簇执行量子形状振荡的能力，换句话说，即同时处于两个不同形状的量子叠加中。这一实验观察将揭示在纳米尺度上出现的量子行为的一个新的和独特的情况。这项研究在概念上也与核物理和超冷原子云物理有很大的重叠，并可能在光学纳米电子学中得到应用。在人力资源方面，该项目将在一个固有的跨学科领域的广泛实验和理论方面为研究生提供出色的培训。博士后研究人员将接受专业指导。对教学和外展的承诺包括本科生持续积极地参与研究，以及为大学项目、科学博览会和国内和国际本科生研讨会做出贡献。

This research project employs the experimental techniques and capabilities of beams of mass-selected atomic nanoclusters to investigate two types of quantum phenomena, both of fundamental character but also of important practical significance. The first subject involves the influence of long-range potentials 'those of large permanent dipoles' on inelastic collisions. Specifically, absolute cross sections for electron capture by a very strong electric dipole field will be measured for the first time. In addition, the heretofore unexplored influence of a giant magnetic dipole on the capture process will be explored. Atomic clusters represent uniquely suitable targets for such measurements. The second part of the project will identify a novel quantum resonance existent at nanoscale dimensions: a cluster particle in a state corresponding to a quantum linear superposition of two geometric shapes. This identification will be accomplished via laser spectroscopy of free metal clusters with a well-defined size and isotopic composition. Optical spectroscopy of size-selected metal clusters exhibiting electronic shell structure (a.k.a. "artificial atoms") will be used to detect the influence of their isotopic mass on the collective electron resonance absorption. This peculiar isotope effect will reveal the presence of a novel quantum resonance phenomenon in the nanoscale domain: quantum superposition of cluster shape configurations.Atomic clusters are nanoscale aggregates made up of a finite number of atoms, from a few to thousands. They bridge the gap between individual atoms and molecules on one end, and larger particles (such as microstructures and aerosols) and bulk materials on the other. The ability to adjust precisely the cluster size and composition allows one to prepare quantum-size objects with useful and unusual features, and to investigate novel physical phenomena associated with these features. One property, utilized in this project, is the capability of certain clusters to generate extremely strong electric and magnetic fields in their vicinity, and to use these fields to attract and capture nearby charged particle, e.g. electrons. The project will measure the efficiency of this process, heretofore never explored for field intensities as high as those generated by the "polar" clusters. In addition to providing new fundamental insight, the results will have practical implications for understanding the interactions of ultracold molecules and ions, for the goal of achieving control of chemical reactions by externally applied fields, for investigation of magnetic nanoparticles, and for understanding processes occurring in atmospheric and interstellar environments. In the second part of the project, the ability of nanoclusters to execute quantum shape oscillations in other words, to be in a quantum superposition of two different shapes at the same time will be investigated. This experimental observation will reveal a new and distinctive case of quantum behavior appearing at the nanometer length scale. This research also has a strong conceptual overlap with nuclear physics and with the physics of ultracold atomic clouds, and may have applications in optical nanoelectronics. On the human resources side, the project will offer graduate students excellent training in a wide range of experimental and theoretical aspects of an inherently interdisciplinary field. Postdoctoral researchers will receive professional mentoring. Commitment to teaching and outreach includes ongoing active undergraduate student involvement in research, as well as contributions to university programs, science fairs, and workshops for domestic and international undergraduates.