Fluctuation-induced drift in a gravitationally tilted optical lattice

TL;DR

This paper investigates how tiny gravitational tilts in an optical lattice cause measurable drift in Brownian particles, combining experiments with theoretical models to explore fundamental statistical physics.

Contribution

It demonstrates the use of cold atoms in optical lattices as a precise testbed for studying fluctuation-induced drift and compares simplified and semi-classical models with experimental data.

Findings

Good qualitative agreement between models and experiments

Control and measurement precision enable fundamental physics tests

Drift magnitude depends on bias force and potential ratio

Abstract

Experimental and theoretical studies are made of Brownian particles trapped in a periodic potential, which is very slightly tilted due to gravity. In the presence of fluctuations, these will trigger a measurable average drift along the direction of the tilt. The magnitude of the drift varies with the ratio between the bias force and the trapping potential. This can be closely compared to a theoretical model system, based on a Fokker-Planck-equation formalism. We show that the level of control and measurement precision we have in our system, which is based on cold atoms trapped in a 3D dissipative optical lattice, makes the experimental setup suitable as a testbed for fundamental statistical physics. We simulate the system with a very simplified and general classical model, as well as with an elaborate semi-classical Monte-Carlo simulation. In both cases, we achieve good qualitative agreement with experimental data.