An apparatus for measuring short-range deviations from Newtonian gravity including a magnetic force calibration

Several recent theories suggest that new physics related to gravity may appear at short length scales. For example, light moduli or particles in ``large'' extra dimensions could mediate macroscopic forces of(super)gravitational strength at length scales below a millimeter. We have built an apparatus utilizing cryogenic micro-cantilevers capable of measuring atto-Newton forces [1] which now includes a magnetic analog for force calibration. Our most recent experimental constraints on Yukawa-type deviations from Newtonian gravity will be presented. References: [1] J. Chiaverini, S. J. Smullin, A. A. Geraci, D. M. Weld, A. Kapitulnik, Phys.Rev.Lett. {\bf{90}}, 151101 (2003). S. J. Smullin, A.A.Geraci, D.M.Weld, J.Chiaverini, S.Holmes, and A. Kapitulnik, Phys. Rev. {\bf{D 72}}, 122001 (2005).