Monteiro works on the theory and control of levitated optomechanical systems, including a stable 3D velocity feedback cooling scheme for independently controlling all three translational modes of an optically levitated nanoparticle with minimal cross-talk. Levitated optomechanics of this kind is being developed both as a force/impulse sensor of exquisite sensitivity and, in collaboration with UCL colleagues including Peter Barker, as a testbed for macroscopic quantum states relevant to proposed gravity-entanglement experiments.