Searching for new physics at the micron scale with optically levitated microspheres

While gravity is in many respects the most extensively studied of the fundamental interactions, its nature at short length scales remains unexplored. Efforts to reconcile general relativity with quantum mechanics or to resolve the hierarchy problem often involve postulating the existence of extra dimensions at the micron scale; in addition, many extensions to the Standard Model predict interactions mediated by new light bosons. New physics of this kind can be parameterized by a Yukawa-like modification to Newtonian gravity at short distances. To search for modified gravity, our group uses optically levitated silica microspheres as force sensors, capable of achieving attonewton sensitivity. This experimental technique is complementary to other methods like torsion balances without being subject to the same systematic effects. In this talk, I will present the status of ongoing upgrades to the experiment since the initial results and discuss prospects for a future run capable of cutting into new parameter space.