Coherent Diffraction Imaging with Superfluid He Nano-Droplets

一个世纪以来，液氦的超流动性一直吸引着凝聚态物理学家，直到今天仍然是一个非常有趣的话题。这种行为是宏观量子效应的一个例子，类似于发生在某些材料中的超导行为。在液氦中，这种宏观量子行为以许多迷人的方式表现出来，其中之一是正常液体所表现出的粘度消失了。这导致了许多有趣的现象，如长寿命量子涡旋线的出现。本项目将利用直线加速器相干光源新研制的x射线自由电子激光器，探索悬浮氦气液滴的流体动力学。这项研究将产生的新见解将有助于我们理解涡旋对从超导体到中子星等系统的影响。此外，在这个项目中开发的工具将对材料科学家开发新的纳米材料有很大的好处。本项目将探索4-He液滴的量子旋转，为中观量子流体力学带来新的物理见解。特别是，本研究将：(i)有助于描述在可用角动量-角速度相空间中的旋转量子液滴，并确定旋转超流体和经典液滴是否属于同一形状族；（ii）提供液滴中静止的涡流（N = 1-200）的形状和构型，这些形状和构型尚未在实验或理论上进行研究；（iii）通过研究Xe簇修饰的涡，揭示涡质量对其动力学的影响；（iv）阐明极端涡度下的量子旋转，比体实验高出约100000倍，为量子液体中未探索的旋转激发机制提供了途径。利用直线相干光源自由电子激光的单次飞秒x射线相干衍射成像，结合新的图像重建算法，重建液滴形状和液滴内涡旋位置的真实空间图像。

Non-technical AbstractSuperfluidity in liquid helium has fascinated condensed matter physicists for a century and remains a topic of great interest even today. This behavior is an example of a macroscopic quantum effect similar to the superconducting behavior that occurs in some materials. In liquid helium this macroscopic quantum behavior manifests itself in many fascinating ways one of which is the disappearance of the viscosity exhibited by normal liquids. This leads to many interesting phenomena such as the appearance of long lived quantum vortex lines. This project will make use of the newly developed x-ray free electron laser at the Linac Coherent Light Source to explore the hydrodynamics of feely suspended helium droplets. The new insights this research will produce will help in our understanding of the effects of vortices on systems ranging from superconductors to neutron stars. In addition, the tools that will be developed during this project will be of great benefit to materials scientists developing new nanomaterials.Technical AbstractThis project will explore quantum rotation in 4-He droplets to bring new physical insights into quantum hydrodynamics at the meso-scale. In particular, this study will: (i) contribute to the description of rotating quantum droplets across the available angular momentum - angular velocity phase space and determine if the rotating superfluid and classical droplets belong to the same families of shapes; (ii) provide stationary shapes and configurations of vortices (N = 1-200) in a droplet, which remain unstudied experimentally or theoretically; (iii) reveal the effect of vortex mass on their dynamics by studying vortices decorated with Xe clusters; and (iv) elucidate quantum rotation at extreme vorticity, up to a factor of about 100000 higher than attained in bulk experiments, providing access to unexplored regimes of rotational excitation in quantum liquids. Single-shot femtosecond X-ray coherent diffractive imaging at the Linac Coherent Light Source free electron laser coupled with new image reconstruction algorithms will be used to reconstruct real space images of the shape of the droplets and the location of vortices within the droplet.