Force sensing with an optically levitated charged nanoparticle

Levitated optomechanics is showing potential for precise force measurements. Here, we report a case study to show experimentally the capacity of such a force sensor, using an electric field as a tool to detect a Coulomb force applied onto a levitated nanosphere. We experimentally observe the spatial displacement of up to 6.6 nm of the levitated nanosphere by imposing a DC field. We further apply an AC field and demonstrate resonant enhancement of force sensing when a driving frequency, ωAC, and the frequency of the levitated mechanical oscillator, ω0, converge. We directly measure a force of 3.0 ± 1.5 × 10–20 N with 10 s integration time, at a centre of mass temperature of 3 K and at a pressure of 1.6 × 10–5 mbar.