Testing Newtonian gravity at the nanometer distance scale using the iso-electronic effect

We describe a new experimental and theoretical effort to search for new forces and extra spatial dimensions over nanometer distance scales. Since the Casimir force produces a large background over these distances, we plan to base our experiments on the iso-electronic effect. This utilizes the observation that the Casimir force depends primarily on the electronic properties of the test bodies, whereas new long-ranged forces also couple to nuclei. By measuring force differences between isotopes of the same element, we hope to greatly improve the current limits on new forces and extra dimensions at submicron separations.