Force Sensing at the Quantum Limit with Levitated Microspheres: sensing and interferometry with a standing-wave trap

Understanding the nature of gravity at microscopic distances is one of the most important open problems in fundamental physics. Although General Relativity provides a well-tested framework for describing gravitational e�ects at large distances, it cannot be consistently combined with the Standard Model of particle physics to provide a description of gravity at small distance scales. The development of a quantum theory of gravity that can be incorporated into the Standard Model is a central goal of physics, with broad implications for our understanding of particle physics and the nature of the \dark energy" that appears to permeate the universe. Many theories attempting to provide a consistent microscopic framework for gravity (e.g., those involving extra dimensions) predict that gravity could deviate from the familiar inverse square law, 1=R2, at distances R < 1 mm. Yet, such deviations are extremely difficult to measure due to the weakness of gravitational interactions. Previous measurements at these distance scales have employed techniques derived from human-size devices in which mechanical springs are used as force sensors. The progress in this challenging �eld is slow, and new methodologies building on modern technologies that naturally enable the fabrication and manipulation of micron-scale objects are bound to substantially advance the state-of-the-art. Combining these modern microfabrication techniques with advances in optical manipulation of microscopic objects will enable new tests of the nature of gravity at short distance with unprecedented precision.