Measuring Gravity at the Micron Scale with Laser-Cooled Trapped Microspheres: a Continuation

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This award is supported by the Gravitational Physics and the Atomic, Molecular and Optical Experimental Physics programs. Gravity is by far the least understood fundamental force of nature. One particular mystery has to do with why gravity is so much weaker than the other Standard Model forces in nature. As a number of recent theories have suggested, important clues related to this "hierarchy problem" can be obtained by measuring how gravity behaves at sub-millimeter distances. Such measurements could lead to exciting new discoveries of physics beyond the Standard Model. However, the gravitational force between massive objects becomes weak very rapidly as their size and separation distance decreases, thus making ultra-sensitive measurements a necessity at sub-millimeter length scales. This group is developing an experiment based on new technology which could advance our understanding of gravity by several orders of magnitude at the micrometer length scale. In this approach, a fused silica test mass is suspended in a "container" made of light, leading to greatly reduced friction and enhanced sensitivity. The students and postdoctoral researchers working on this project will be broadly trained in experimental physics and nanofabrication and will be well positioned for entry into the scientific workforce. The fundamental nature of this project appeals to our sense of wonder about the natural world. 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.This award supports an experiment which uses laser-cooled trapped microspheres to test for Yukawa-type deviations from Newtonian gravity at the micron length scale. By optically levitating the force sensor, an exquisite de-coupling from the environment is possible, yielding sub aN-Hz^1/2 force sensitivity at room temperature. This new technique could ultimately advance our understanding of gravity at the micron length scale by a factor of 1,000 to 100,000, and may lead to ground-breaking discoveries. In addition to studies of short-range gravitational forces, the proposed experimental technique will also enable novel investigations of Casimir forces in unexplored regimes. The project is conceptually divided into three tasks: (1) refinement of techniques to position levitated nanospheres within few-micron distances from a source mass surface, (2) investigation of systematic errors in preliminary gravity measurements, (3) in-parallel development of novel methods for trapping and cooling the levitated nanoparticles, including sympathetic cooling with cold atoms. One graduate student, one undergraduate student, and one postdoctoral researcher will be broadly trained in experimental physics and nanofabrication, and encouraged to present results at scientific meetings. By participating in this highly interdisciplinary research project, students will be well equipped for scientific careers. In addition, efforts to include women and minority researchers in the project will be undertaken.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.