CAREER: Macroscopic Quantum Measurement and Control to Probe Gravity

The behavior of objects at the scale of atoms, or smaller, is well described by the laws of quantum mechanics. The behavior of large objects, such as the earth or the galaxy, is well described by Einstein’s theory of gravity. However, these two descriptions of our universe do not appear to be fully compatible, and a challenge of contemporary physics is to find a way to bridge this seeming incompatibility. One difficulty with doing this is the fact that the gravitational force between atomic-scale objects is too weak to measure. To overcome this problem, the PI and his students are planning to perform experiments on centimeter-scale objects, which have significant gravitational interactions, with a precision that approaches the limits allowed by quantum mechanics. Additionally, the PI will author a textbook that uses an inter-disciplinary approach to the theory and practice of realistic quantum measurements. This textbook will help train the next generation of quantum engineers. The research program will extend recently demonstrated techniques to fabricate multi-centimeter-scale, mass-loaded, high-stressed torsional suspensions with mechanical quality factors of at least 100 million. The angular displacement of such a torsional oscillator will be measured and controlled in a quantum-noise-limited manner. The torsional pendulum will be used as a “probe mass” to detect the gravitational force of a driven, milligram-scale “source mass”. Techniques will be developed to simultaneously isolate gravitational interaction and realize quantum-limited and quantum-noise-evading operation. 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.