Search for Screened Interactions Associated with Dark Energy Below the 100 $\mathrm{μm}$ Length Scale

We present the results of a search for unknown interactions that couple to mass between an optically levitated microsphere and a gold-coated silicon cantilever. The scale and geometry of the apparatus enables a search for new forces that appear at distances below 100 $μ$m and which would have evaded previous searches due to screening mechanisms. The data are consistent with electrostatic backgrounds and place upper limits on the strength of new interactions at $<0.1$ fN in the geometry tested. For the specific example of a chameleon interaction with an inverse power law potential, these results exclude matter couplings $β> 5.6 \times 10^4$ in the region of parameter space where the self-coupling $Λ\gtrsim 5$ meV and the microspheres are not fully screened.