Stochastic and equilibrium pictures of the ultracold FFR molecular conversion rate

TL;DR

This paper compares stochastic phase space sampling and chemical equilibrium theory models to understand ultracold FFR molecular conversion rates across different atomic symmetries, highlighting differences in BEC-influenced scenarios.

Contribution

It applies and compares two statistical models to ultracold molecular conversion, revealing their similarities and differences, especially in BEC conditions.

Findings

Models generally agree in most cases

Significant differences arise with Bose-Einstein condensates

Phase-space criteria influence molecular conversion predictions

Abstract

The ultracold molecular conversion rate occurring in an adiabatic ramp through a Fano-Feshbach resonance is studied and compared in two statistical models. One model, the so-called stochastic phase space sampling (SPSS)[E.Hodby et al., PRL.94 120402(2005)] evaluates the overlap of two atomic distributions in phase space by sampling atomic pairs according to a phase-space criterion. The other model, the chemical equilibrium theory(ChET)[S.Watabe and T.Nikuni, PRA.77 013616(2008)] considers atomic and molecular distributions in the limit of the chemical and thermal equilibrium. The present study applies SPSS and ChET to a prototypical system of K+K K2 in all the symmetry combinations, namely Fermi-Fermi, Bose-Bose, and Bose-Fermi cases. To examine implications of the phase-space criterion for SPSS, the behavior of molecular conversion is analyzed using four distinct geometrical constraints. Our comparison of the results of SPSS with those of ChET shows that while they appear similar in most situations, the two models give rise to rather dissimilar behaviors when the presence of a Bose-Einstein condensate (BEC) strongly affects the molecule formation.