# Large-deviations for spatial diffusion of cold atoms

## TL;DR

This paper applies large-deviations theory to analyze the rare, tail events in the spatial diffusion of laser-cooled atoms, revealing a bi-fractal spreading behavior influenced by laser-induced friction.

## Contribution

It introduces a novel approach using nonnormalized infinite-covariant density to study rare events in atomic diffusion with a new friction mechanism.

## Key findings

- Identification of fat-tailed density at intermediate scales
- Discovery of bi-fractal nature in spreading packet
- Application of large-deviations theory to cold atom diffusion

## Abstract

Large-deviations theory deals with tails of probability distributions and the rare events of random processes, for example spreading packets of particles. Mathematically, it concerns the exponential fall-of of the density of thin-tailed systems. Here we investigate the spatial density $P_t(x)$ of laser cooled atoms, where at intermediate length scales the shape is fat-tailed. We focus on the rare events beyond this range, which dominate important statistical properties of the system. Through a novel friction mechanism induced by the laser fields, the density is explored with the recently proposed nonnormalized infinite-covariant density approach. The small and large fluctuations give rise to a bi-fractal nature of the spreading packet.