PM: Measuring Gravity at the Micron-Scale with Laser-Cooled Trapped Microspheres: A Renewal Proposal

重力是自然界已知的四种基本作用力中最不为人所知的。与其他三种标准模型力相比，它的弱点使得在实验中精确测量重力特别具有挑战性。粒子物理标准模型之外的理论，包括弦理论和超对称性，已经有几个预言，牛顿引力平方反比定律将在毫米尺度以下的某个距离崩溃。为了验证这些理论，发展了一种以光陷激光冷却玻璃微珠作为测试质量，以微制造的硅和金器件作为源质量的方法。当被高真空环境包围时，玻璃微珠受到的摩擦力非常小，成为一种超精密的测力仪器，需要测量如此近距离物体之间的微弱引力相互作用。同时，采用扫描和筛选的方法消除不需要的电磁背景力的系统影响。据估计，该方法可以将在微米长度尺度上对引力反平方律的修正的搜索提高三个数量级以上。一名研究生和一名博士后研究员将接受实验物理和纳米制造方面的广泛培训。通过参与这一高度跨学科的研究项目，学生将为从事科学事业做好准备，并将努力纳入来自代表性不足的少数群体的研究人员。这个项目的基本性质可以向普通公众灌输一种对自然世界的好奇感。国家将受益于对与微米尺度的引力物理相关的高能物理的更好理解，而成本只有粒子对撞机实验的一小部分。在这个项目中，将继续开展一项实验，利用激光冷却捕获的微球在微米尺度上测试汤川类型的牛顿引力偏差。这项新技术可以在这种长度尺度上将对重力的理解提高三个数量级以上，并可能导致突破性的发现。在先前结果的基础上，包括校准的zeptonewton力灵敏度和开发出在距离源质量表面微米距离内可靠地操纵三维纳米球的技术，该项目的下一阶段在概念上分为两项任务：(1)调查初步重力测量中的系统误差，目标是在∼1μm尺度的专用汤川力搜索中获得数以百万计的综合数据，以及(2)同时开发捕获和冷却悬浮纳米粒子的新方法，这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Gravity is the least well understood of the four known fundamental forces in Nature. Its weakness when compared to the other three Standard Model forces makes gravity particularly challenging to measure precisely in experiments. There have been several predictions from theories beyond the Standard Model of particle physics, including string theory and supersymmetry, that the Newtonian gravitational inverse square law will break down at some distance below the millimeter scale. To put these theories to the test, a method using an optically-trapped laser-cooled glass bead as a test mass and a microfabricated silicon and gold device as a source mass has been developed. When surrounded by a high-vacuum environment, the glass bead experiences very little friction and becomes an ultraprecise force measurement instrument, needed to measure feeble gravitational interactions between objects at such close ranges. At the same time, scanning and screening methods are employed to eliminate systematic effects from undesired electromagnetic background forces. It is estimated that the method can improve the search for corrections to the gravitational inverse square law at the micron length scale by more than three orders of magnitude. One graduate student and one postdoctoral researcher will be broadly trained in experimental physics and nanofabrication. By participating in this highly interdisciplinary research project, students will be well equipped for scientific careers, and efforts to include researchers from under-represented minorities will be undertaken. The fundamental nature of this project can instill a sense of wonder about the natural world in the general public. The nation will benefit from an improved understanding of high-energy physics related to gravitational physics at the micron length scale, at a fraction of the cost of particle-collider experiments. In this project, an experiment will continue to be developed which makes use of laser-cooled trapped microspheres to test for Yukawa-type deviations from Newtonian gravity at the micron length scale. This new technique can advance the understanding of gravity at this length scale by over three orders of magnitude and may lead to ground-breaking discoveries. Building on previous results, including calibrated zeptonewton force sensitivity and the development of techniques to reliably maneuver nanospheres in three-dimensions within micron-distances from a source mass surface, the next phase of the project is conceptually divided into two tasks: (1) investigation of systematic errors in preliminary gravity measurements, with a goal of acquiring millions of integrated data in a dedicated Yukawa-force search at the ∼ 1 μm-scale, and (2) in-parallel development of novel methods for trapping and cooling the levitated nanoparticles, including sympathetic cooling with cold atoms.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.