Superfluidity in Helium Nanodroplets

非技术摘要该项目的重点是由氦制成的纳米级液滴的性质，氦在绝对零度（-460 °F）下保持液态。在足够低的温度下，液滴没有任何粘性，在这一点上，它们被称为超流体。超流性是一种量子现象，自20世纪初发现以来，它一直是一个非常富有成果的研究领域。有关超流体的理论预测，旋转的超流体液滴包含一组漩涡，但这种漩涡在很长一段时间内都无法观察到。最近，首席研究员和他的学生开发了一种新的技术，通过使液滴受到X射线辐射来成像液滴中的漩涡，并证明液滴可以维持密集阵列中的许多漩涡。这项技术的进一步发展及其对不同种类液滴的应用将提供有关超流液滴性质的新信息，这些信息对有限量子系统的物理学具有根本的重要性。此外，研究高密度下的涡旋将有助于更深入地理解普通流体的物理特性和极端湍流下涡旋的影响，这适用于飞机和船舶的高速运动。此外，该项目还为本科生和研究生提供了参与前沿科学和后续出版物的机会，这加强了美国STEM劳动力。技术摘要该项目的重点是在氦纳米液滴中的中尺度量子流体力学的研究。的液滴产生后，在真空中的加压氦在T 10 K的膨胀，并通过使用直线加速器相干光源自由电子激光器（XFEL）的X射线相干衍射成像询问。 本文揭示了不同形状和角动量的4 He液滴中涡旋的三维排列以及嵌入质量对涡旋运动学的影响。此外，这项工作正在将XFEL实验扩展到3 He和3 He-4 He混合液滴，目的是研究旋转混合液滴中的相分离，包括可能观察到的非平衡超流相，以及纯非超流3 He液滴中的旋转。拟议的实验将提供基准信息的结构，稳定性和旋转动力学的自由旋转的超流体和非超流体液滴。与这些实验一起开发的液滴相干衍射成像算法将能够提供从衍射图案的实时图像重建的第一个实例。

Nontechnical AbstractThis project focuses on the properties of nanoscopic droplets made from helium, which remains liquid at temperatures down to absolute zero (-460 °F). At low enough temperatures, the droplets lack any viscosity, at which point they are said to be superfluid. Superfluidity is a quantum phenomenon, and it has been a very fruitful field of study since its discovery in the early 1900's. Theories pertaining to superfluids predicted that a rotating superfluid droplet contains a collection of vortices, but such vortices evaded observation for a long time. Recently, the principal investigator and his students have developed a novel technique for imaging vortices in the droplets, by subjecting the droplets to x-ray radiation, and proved that droplets can sustain many vortices in dense arrays. Further development of this technique and its applications to different kinds of droplets will provide new information on the properties of superfluid droplets, which are of fundamental importance for the physics of finite quantum systems. Moreover, studying vortices at high density will contribute to a deeper understanding of the physics of ordinary fluids and the effect of vortices at extreme turbulence, which is applicable to the motion of planes and ships at high velocity. Additionally, this project provides opportunities for undergraduate and graduate students to take part in cutting-edge science and ensuing publications, which strengthens the US STEM workforce.Technical AbstractThis project focuses on the study of quantum hydrodynamics at the meso-scale in helium nanodroplets. The droplets are produced upon expansion of pressurized helium in vacuum at T 10 K and are interrogated via x-ray coherent diffraction imaging using the Linac Coherent Light Source free electron laser (XFEL). This work uncovers the three-dimensional arrangement of vortices in the 4He droplets of different shape and angular momentum and the effect of the embedded mass on vortex kinematics. In addition, the work is expanding the XFEL experiments to 3He and mixed 3He-4He droplets with the objective of studying phase separation in rotating mixed droplets, including possible observation of the non-equilibrium superfluid phase, and rotation in the neat non-superfluid 3He droplet. The proposed experiments will provide benchmark information on the structure, stability and rotational dynamics of free rotating super- and non-superfluid droplets. The droplet coherent diffraction imaging algorithm developed alongside these experiments will be able to provide the first instance of real-time image reconstructions from diffraction patterns.