Direct observation of ballistic Brownian motion on a single particle

TL;DR

This paper reports the first experimental observation of ballistic Brownian motion in a single particle using a novel high-bandwidth detector, confirming theoretical predictions about motion at very short timescales.

Contribution

The study introduces a new detector capable of capturing high-frequency Brownian motion, enabling direct observation of ballistic motion and velocity autocorrelation in a single particle.

Findings

First measurement of ballistic Brownian motion

Velocity autocorrelation function determined experimentally

Data aligns with theoretical models including inertia and hydrodynamics

Abstract

At fast timescales, the self-similarity of random Brownian motion is expected to break down and be replaced by ballistic motion. So far, an experimental verification of this prediction has been out of reach due to a lack of instrumentation fast and precise enough to capture this motion. With a newly developed detector, we have been able to observe the Brownian motion of a single particle in an optical trap with 75 MHz bandwidth and sub-{AA}ngstrom spatial precision. We report the first measurements of ballistic Brownian motion as well as the first determination of the velocity autocorrelation function of a Brownian particle. The data are in excellent agreement with theoretical predictions taking into account the inertia of the particle and the surrounding fluid as well as hydrodynamic memory effects.