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, ω_AC, and the frequency of the levitated mechanical oscillator, ω₀, converge. We directly measure a force of 3.0 pm 1.5 times 10^-20 N with 10 second integration time, at a centre of mass temperature of 3 K and at a pressure of 1.6 times 10^-5 mbar.