Thermalization and Sub-Poissonian Density Fluctuations in a Degenerate Molecular Fermi Gas

TL;DR

This paper demonstrates thermalization in a degenerate molecular Fermi gas of polar molecules, measuring elastic scattering and density fluctuations to characterize the quantum state and equilibrium dynamics.

Contribution

It provides the first measurement of atom-dimer elastic scattering near a Feshbach resonance and observes sub-Poissonian fluctuations indicating quantum degeneracy.

Findings

Rapid thermalization of molecules with atomic species

Sub-Poissonian density fluctuations observed

Direct evidence of molecular Fermi--Dirac distribution

Abstract

We observe thermalization in the production of a degenerate Fermi gas of polar ${}^{40}\text{K}{}^{87}\text{Rb}$ molecules. By measuring the atom--dimer elastic scattering cross section near the Feshbach resonance, we show that Feshbach molecules rapidly reach thermal equilibrium with both parent atomic species. Equilibrium is essentially maintained through coherent transfer to the ground state. Sub-Poissonian density fluctuations in Feshbach and ground-state molecules are measured, giving an independent characterization of degeneracy and directly probing the molecular Fermi--Dirac distribution.