Interrogation and Manipulation of Coherences in Superfluid Helium

在这个由化学部实验物理化学项目资助的项目中，Apkarian将进行一个旨在研究大块超流氦（He-II）基础的实验研究项目。总体目标是研究系统的微观含义，主要是其量子集体动力学，以便通过多线性光谱操纵相干。超流氦流是近年来作为通用分子注入器的载流而发展起来的，但其性质尚未得到充分的了解。纯流的性质，即突然膨胀的玻色凝聚体的性质，具有基本的和实际的意义。流将被表征为脉冲膨胀条件的函数，如储层温度、压力、脉冲长度和喷嘴设计。光散射将用于表征从液滴到连续流的转变；干涉成像将用于量化流的密度和散度；二次谐波将用于表征有序涡度。将用光谱学研究流中携带的分子杂质。在其他研究中，将通过时间/频率分辨CARS光谱研究流嵌入的氢分子，氢的相干旋转将用于研究氢团簇的大小依赖于液固转变以及这些团簇可能的超流动性。研究生和本科生以及博士后研究人员将通过参与这项研究获得宝贵的经验，该研究涉及低温工程，光学工程，现代激光技术，以及在1k下使用分子操作技术。几乎所有科学的核心领域，包括经典和量子力学，都将被用于这项研究，结果是参与者将有一个不同寻常的丰富的学习和培训经验。

In this project, funded by the Experimental Physical Chemistry Program of the Chemistry Division, Apkarian will conduct an experimental research program aimed at fundamental studies of bulk superfluid helium (He-II). The general goals are to investigate microscopic implications of the system, principally its quantum collective dynamics in order to manipulate coherences through multilinear spectroscopy. Superfluid helium streams were recently developed as the carrier fluid in a universal molecule injector, but their properties are not yet sufficiently understood. The properties of the neat stream, namely of a suddenly expanded Bose condensate, are of fundamental and practical interest. The streams will be characterized as a function of the pulsed expansion conditions, such as reservoir temperature, pressure, pulse length, and nozzle design. Light scattering will be used to characterize transitions from droplet to continuous flow; interferometric imaging will be used to quantify density and divergence of the stream; and second harmonic generation will be use to characterize ordered vorticity. Molecular impurities entrained in the stream will be studied spectroscopically. Among additional studies there will be investigations of stream-embedded hydrogen molecules by means of time/frequency resolved CARS spectroscopy, and the coherent rotations of hydrogen will be used to investigate the size dependent liquid-solid transition of hydrogen clusters and the possible superfluidity of these clusters. Graduate and undergraduate students as well as postdoctorate researchers will gain valuable experience through participation in this research, which involves cryogenic engineering, optical engineering, and modern laser techniques, as well as the use of techniques involved in molecular manipulations at 1 K. Nearly all core areas of the sciences, both classical and quantum mechanical, will be used in this research, with the result that the participants will have an unusually rich learning and training experience.