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

在自然界已知的四种基本力中，引力是最不为人所知的。与其他三种标准模型力相比，引力的弱点使得在实验中精确测量引力变得特别困难。粒子物理学标准模型之外的理论，包括弦理论和超对称理论，已经做出了一些预测，认为牛顿引力平方反比定律将在毫米尺度以下的距离上失效。为了验证这些理论，研究人员开发了一种方法，使用光捕获激光冷却的玻璃珠作为测试质量，并用微制造的硅和金器件作为源质量。当被高真空环境包围时，玻璃珠的摩擦力很小，成为一种超精密的力测量仪器，用于测量如此近距离物体之间微弱的引力相互作用。同时，采用扫描和筛选方法来消除不希望的电磁背景力对系统的影响。据估计，该方法可以将在微米尺度上寻找引力平方反比定律修正的速度提高三个数量级以上。一名研究生和一名博士后将在实验物理和纳米制造方面接受广泛的培训。通过参与这个高度跨学科的研究项目，学生们将为科学事业做好准备，并将努力包括来自代表性不足的少数民族的研究人员。这个项目的基本性质可以向公众灌输一种对自然世界的好奇感。这个国家将受益于在微米尺度上对与引力物理相关的高能物理的更好理解，而花费的费用只是粒子对撞机实验的一小部分。在这个项目中，将继续开发一个实验，利用激光冷却的捕获微球在微米尺度上测试与牛顿引力的汤川型偏差。这项新技术可以将对这种长度尺度的引力的理解提高三个数量级以上，并可能带来突破性的发现。基于先前的结果，包括校准的齐普顿力灵敏度和技术的发展，在距离源质量表面微米距离的三维范围内可靠地操纵纳米球，项目的下一阶段在概念上分为两个任务：(1)研究初步重力测量中的系统误差，目标是在1 μm尺度上通过专门的汤川力搜索获得数百万个集成数据；(2)并行开发捕获和冷却悬浮纳米粒子的新方法，包括冷原子的共感冷却。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。

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.