Non-equilibrium steady state of a driven levitated particle with feedback cooling

TL;DR

This paper investigates the non-equilibrium steady state of a laser-trapped nanoparticle under feedback cooling and parametric modulation, providing analytical, simulation, and experimental insights into energy control and thermal squeezing effects.

Contribution

It presents a combined theoretical, simulation, and experimental study deriving an analytical energy distribution for a driven levitated particle in a non-equilibrium steady state.

Findings

Analytical expression for energy distribution matches simulations and experiments.

Energy and variance can be independently controlled via system parameters.

Thermal squeezing observed depending on detuning degree.

Abstract

Laser trapped nanoparticles have been recently used as model systems to study fundamental relations holding far from equilibrium. Here we study, both experimentally and theoretically, a nanoscale silica sphere levitated by a laser in a low density gas. The center of mass motion of the particle is subjected, at the same time, to feedback cooling and a parametric modulation driving the system into a non-equilibrium steady state. Based on the Langevin equation of motion of the particle, we derive an analytical expression for the energy distribution of this steady state showing that the average and variance of the energy distribution can be controlled separately by appropriate choice of the friction, cooling and modulation parameters. Energy distributions determined in computer simulations and measured in a laboratory experiment agree well with the analytical predictions. We analyse the particle motion also in terms of the quadratures and find thermal squeezing depending on the degree of detuning.