Constraining new forces in the casimir regime using the isoelectronic technique

We report the first application of the isoelectronic technique (IET) to set limits on new forces over the 10-100 nm distance scale. In the IET a differential measurement is made which directly compares the force between an Au-coated probe and two Au-coated films, made out of Au and Ge. The thickness of the common Au-coating is adjusted so that, in the absence of forces other than the known Casimir force, no differential signal would be detected as the probe oscillates between the Au and Ge films. By not having to resort to detailed theoretical descriptions of the Casimir interaction, and using soft microelectromechanic al torsional oscillators, the experimental sensitivity is greatly improved. The measured differential signal is directly converted into limits on the standard parameters á and ë which characterize Yukawa-like deviations from Newtonian gravity. We find an improvement of 10 over previous limits.