Anisotropic expansion of a thermal dipolar Bose gas

TL;DR

This paper investigates the anisotropic expansion of thermal dipolar Bose gases, develops a comprehensive theory including interactions and quantum effects, and introduces a precise thermometry method and a way to determine scattering lengths.

Contribution

It provides a new quantitative model for anisotropic expansion of dipolar Bose gases and a practical method for accurate thermometry and scattering length measurement.

Findings

Extended expansion thermometry accuracy from tens of percent to a few percent.

Developed a model incorporating Hartree-Fock interactions, hydrodynamics, and Bose-enhancement.

Proposed a simple method to measure scattering lengths near Feshbach resonances.

Abstract

We report on the anisotropic expansion of ultracold bosonic dysprosium gases at temperatures above quantum degeneracy and develop a quantitative theory to describe this behavior. The theory expresses the post-expansion aspect ratio in terms of temperature and microscopic collisional properties by incorporating Hartree-Fock mean-field interactions, hydrodynamic effects, and Bose-enhancement factors. Our results extend the utility of expansion imaging by providing accurate thermometry for dipolar thermal Bose gases, reducing error in expansion thermometry from tens of percent to only a few percent. Furthermore, we present a simple method to determine scattering lengths in dipolar gases, including near a Feshbach resonance, through observation of thermal gas expansion.