Surface Charge Adsorption as an Unrecognized Systematic in Precision Gravimetry and Atom Interferometry

Laboratory measurements of the gravitational interaction rely on torsion balances and atom-interferometric gravimeters. Both employ metallic test masses that unavoidably acquire sub-monolayer ionic adsorbates and patch potentials when exposed to air or residual gases. Here we show that surface charge densities as small as 10⁻⁶–10⁻⁹ monolayers, corresponding to net charges of 10⁻⁷–10⁻¹⁰ C, are sufficient to generate electrostatic forces and Stark-induced atomic phase shifts comparable to those interpreted as gravitational. Because such charge levels are chemically natural on oxidized tungsten and remain stable even in ultra-high vacuum, current gravimetric experiments do not experimentally isolate gravity from surface-electrostatic artefacts. We propose a charge-controlled interferometric protocol capable of discriminating between the two mechanisms. Given the foundational role of G in astrophysics and cosmology, improved control of these systematics may refine the interpretation of gravitational measurements at all scales.