Macroscopic Quantum Mechanics in Pursuit of Gravity’s Quantum Nature

A pre-eminent problem of modern physics is to reconcile the disparity between the laws of quantum physics – which apply at the small scale – and the laws of gravity – that apply at the large scale. A decisive confrontation of these theories calls for mechanical objects, massive enough to measurably gravitate with each other, prepared in quantum states of their motion. We have been developing the ideas, inventing the tools, and performing demonstrations that pave the way towards such an experiment. This talk will highlight some of these milestones. In particular, we will describe how the motion of tangibly macroscopic mechanical oscillators can be measured and controlled at the quantum level; novel sources of fundamental noises that have been discovered and understood through this quest; quantum limits in the measuring instruments that are used, and their malleability; and novel techniques to expand the reach of laser cooling to centimeter-scale torsional oscillators. Taken together, these advances represent the frontier of precision measurement science with ramifications for macroscopic quantum mechanics, gravitational-wave detection, and time-keeping.