Characterization of Superfluid Helium Dynamics Using Nanoparticles

本项目探讨低温下超流氦的表征。通过将纳米大小的颗粒放入流体中，研究小组观察了量子流体的运动以及其中的龙卷风状漩涡。这项研究既有助于更好地理解这种奇怪的量子物质形式，也有助于理解超导体和其他类似的技术先进材料。该项目还用于培养凝聚态物质实验的新一代学者，包括本科生指导和研究生培训。公众对科学的欣赏是确保我国科技实力的关键组成部分。为了支持公众对科学的欣赏，研究团队向非常广泛的受众提供实验室参观：中学女生（每年一次），高中团体，本科俱乐部，未来的本科生和研究生，访问教师，访问教师和员工家属，访问政府工作人员和科学记者。此外，该团队还提供了简短的教学视频，发布在研究小组的YouTube频道上（www.youtube.com/user/n3umh）.Technical摘要)。这项研究的主要重点是表征超流氦的动力学，并将这些知识应用于定量测试描述量化漩涡运动的理论模型。当量子流体，包括超流体氦，被驱动远离平衡时，它们表现出具有复杂和接近单一动力学的量子化漩涡。这些涡旋控制着超流体和类似系统的动力学，并使系统恢复平衡，表现出远程量子秩序。研究小组开发了世界上独一无二的实验技术和先进的诊断方法来探测这些流动，并开发了量化漩涡动力学的详细定量表征。具体的问题是：1)什么是场方程来表达流动的有序和无序部分的耦合？2)我们的观察，特别是关于重连的观察，对类似系统意味着什么？3)量子湍流和经典湍流在小尺度和大尺度上的异同是什么？4)量化涡流是如何通过lambda跃迁形成的？5)量子化旋涡的三角晶格（在近固体旋转状态下）是如何形成的？6)量子流体中哪些过程打破了时间反转不变性？这些观测结果被用来挑战理论，以更好地理解从超导体到捕获离子玻色-爱因斯坦凝聚物的各种现象。

Nontechnical abstractThis project explores the characterization of superfluid helium at low temperatures. By putting nanometer-sized particles into the flows, the research team observes the motion of the quantum fluid and the tornado like vortices therein. The research serves both to better understand this strange form of quantum matter, and also aids in understanding superconductors and other analogous technologically advanced materials. The project also serves to educate a new generation of scholars in condensed matter experiments, including undergraduate mentoring and graduate student training. The public appreciation of science is a critical component of ensuring our nation's strength in science and technology. In support of public appreciation of science the research team offers lab tours to a very broad range of audiences: middle school girls (annual), high school groups, undergraduate clubs, prospective undergraduate and graduate students, visiting faculty, visiting families of faculty and staff, visiting government staff, and science journalists. In addition the team offers short pedagogical videos, posted on the research group YouTube channel (www.youtube.com/user/n3umh).Technical abstractThe primary focus of this research is to characterize the dynamics of superfluid helium, and to apply this knowledge to quantitatively test theoretical models describing the motion of quantized vortices. When quantum fluids, including superfluid helium, are driven far from equilibrium they exhibit quantized vortices with complex and near-singular dynamics. These vortices control the dynamics of and return the system to equilibrium for both superfluids and similar systems exhibiting long-range quantum order. The research team develops world-unique experimental techniques and advanced diagnostics to probe these flows, and develops detailed quantitative characterization of the quantized vortex dynamics. Specific questions addressed are: 1) What are field equations that express the coupling of the ordered and disordered parts of the flow? 2) What do our observations, especially regarding reconnection, imply about analogous systems? 3) What are the similarities and differences between quantum and classical turbulence at small and large scales? 4) How do quantized vortices form through the lambda transition? 5) How does the triangular lattice of quantized vortices (in the near solid-body rotating state) form? 6) Which processes break time reversal invariance in quantum fluids? The observations are used to challenge theory toward a better understanding of a wide array of phenomena ranging from superconductors to trapped ion Bose-Einstein condensates.