Stabilizing nanoparticles in the intensity minimum: feedback levitation on an inverted potential

TL;DR

This paper presents a feedback control method for stably trapping a nanoparticle at the intensity minimum of an inverted optical potential, enabling precise confinement and potential quantum applications.

Contribution

It introduces the FLIP technique combined with Kalman-filter-based control to stabilize nanoparticles at the potential maximum despite environmental drifts.

Findings

Achieved nanoparticle confinement within 9 nm of the potential maximum.

Maintained effective temperature of 16 K at room temperature.

Demonstrated drift compensation using Kalman filtering.

Abstract

We demonstrate the stable trapping of a levitated nanoparticle on top of an inverted potential using a combination of optical readout and electrostatic control. The feedback levitation on an inverted potential (FLIP) method stabilizes the particle at an intensity minimum. By using a Kalman-filter-based linear-quadratic-Gaussian (LQG) control method, we confine a particle to within $\sigma_x = (9.0 \pm 0.5) nm$ of the potential maximum at an effective temperature of $(16 \pm 1) K$ in a room-temperature environment. Despite drifts in the absolute position of the potential maximum, we can keep the nanoparticle at the apex by estimating the drift from the particle dynamics using the Kalman filter. Our approach may enable new levitation-based sensing schemes with enhanced bandwidth. It also paves the way for optical levitation at zero intensity of an optical potential, which alleviates decoherence effects due to material-dependent absorption and is hence relevant for macroscopic quantum experiments.