medium

Principle of the experiment [5]. Vacuum chamber walls are at ± Z. Solid red curve: scalar field ϕ is small at
±Z, rising to ϕ_bg at the center of the empty chamber. Dashed(dotted) blue curve: ball in position 1(2) perturbs ϕ to produce a gradient ∇ϕ. Atoms at the center of the chamber have acceleration a_ϕ∝∇ϕ
toward the ball, which we measure by atom interferometry.

Figure 1 from https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.061102