Investigating the Nature of Excitations in Superfluid 3He Using MEMS Oscillators

非技术描述：50多年前，一位杰出的理论物理学家和科学作家乔治·伽莫夫（George Gamow）说，只有数论和拓扑学不适用于物理学。尽管如此，自20世纪80年代以来，物理学家开始了解拓扑学在物理学中的重要作用，并且发现了称为拓扑量子物质的新型材料。这些材料具有意想不到的特性，不仅扩展了我们的知识，而且还具有材料的功能。一般来说，这些拓扑材料是由多个具有复杂结构的元素组成的。然而，氦的一种形式，被称为氦- 3同位素，当它在接近绝对零度的极低温度下冷却到液态时，就会变成一种拓扑物质。在这样的条件下，它形成了一种新的物质状态，称为超流体，表现出迷人的量子现象。在这个项目中，PI的研究小组使用一种独特的实验技术，利用小型机械振荡器来研究超流体氦- 3的性质。这个项目将扩大我们对氦- 3这些独特性质的理解。研究小组由研究生和本科生组成一个团队。他们不仅将接受低温物理领域的培训，还将接受硅纳米制造技术的培训，从设计到制造专门的设备，这些设备通过广泛用作传感器和执行器而在我们的现代世界中扩散。技术描述：人们对p波超流体3He中表面Andreev束缚态的兴趣日益浓厚，因为它可以说是研究拓扑激励本质的最完整的平台。PI小组开发了一种基于微机电系统（MEMS）技术的多功能和强大的实验探针，用于研究该系统中的表面Andreev束缚态。主要工作有：(1)研究镜面边界上的拓扑表面态，以全面理解性质，如狄拉克费米子的实验证据和可能的场驱动拓扑跃迁。（ii）研究两个接近表面态之间的相互作用。（iii）以MEMS阵列的形式开发具有空间分辨探测能力的灵敏准粒子磁通传感器。这个项目，在与理论家的密切合作下，肯定会扩大我们对原始拓扑超流体中这些独特激励的理解。理论预测的由小磁场引起的拓扑跃迁的证实将是该系统中对称性保护的拓扑超流体和马约拉纳费米子的最令人信服的表现之一。MEMS阵列的成功开发将为实现3He和4He的空间分辨探测提供前所未有的机会，并具有许多可预见的应用：3He中涡旋的可视化和准粒子的角度分辨探测，以及He-II中动量分辨的转子-声子探测和量子湍流研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical Description:More than 50 years ago, a distinguished theoretical physicist and a science writer George Gamow said that only number theory and topology had no application to physics. Nonetheless, physicists started to understand the significant role of topology in physics since 1980's, and new types of materials called topological quantum matter are being discovered. These materials possess unexpected properties which not only expand our knowledge but also functionality of the materials. In general, these topological materials are composed of multiple elements with complex structures. However, a form of helium, called helium-three isotope, becomes a topological matter when it is cooled down to a liquid form at extremely low temperature close to absolute zero. At such conditions it forms a new state of matter called a superfluid that exhibits fascinating quantum phenomena. In this project, the PI's research group investigates the nature of superfluid helium-three using a unique experimental technique employing small mechanical oscillators. This project will expand our understanding on these unique properties of helium-three. The research group is composed of graduate and undergraduate students working as a team. They will be trained not only in the field of low-temperature physics but also in silicon nanofabrication technology from design to fabrication of specialized devices that have proliferated our modern world through their widespread use as sensors and actuators.Technical Description: Growing interest in the surface Andreev bound states in p-wave superfluid 3He arises from the fact that it is arguably the most complete platform available to investigate the nature of topological excitations. The PI's group has developed a versatile and powerful experimental probe based on Micro-Electro-Mechanical System (MEMS) technology to study the surface Andreev bound states in this system. The major activities are: (i) Investigation of the topological surface states on a specular boundary for comprehensive understanding of the nature such as experimental evidence for Dirac fermions and a possible field-driven topological transition. (ii) Investigation of the interactions between two surface states in close proximity. (iii) Development of a sensitive quasiparticle flux sensor with a spatially resolved detection capability in the form of MEMS arrays. This project, in close collaboration with theorists, will certainly expand our understanding of these unique excitations in a pristine topological superfluid. Confirmation of the theoretically predicted topological transition induced by a small magnetic field would be one of the most convincing manifestation of a symmetry-protected topological superfluid and Majorana fermions in this system. The successful development of MEMS arrays will provide unprecedented opportunities to achieve spatially-resolved detection in 3He and 4He with many foreseeable applications: visualization of vortices and angle-resolved detection of quasiparticles in 3He, and momentum resolved roton-phonon detection and quantum turbulence study in He-II.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.