Bosons and Fermions near Feshbach resonances

TL;DR

This paper explores the properties of Bose and Fermi gases near Feshbach resonances, revealing universal behaviors and pairing phenomena that could enable superfluidity in trapped atomic systems.

Contribution

It provides a quantitative description of strongly interacting Bose and Fermi gases near Feshbach resonances using an approximate wave function approach.

Findings

Energy per particle approaches a universal value proportional to $ ^{2/3}/m$

Pairing gap scales with $ ^{2/3}/m$ and is a large fraction of Fermi energy

Multiple pairing transitions depend on interaction strength and particle number

Abstract

Near Feshbach resonances, $n|a|^3\gg 1$, systems of Bose and Fermi particles become strongly interacting/dense. In this unitary limit both bosons and fermions have very different properties than in a dilute gas, e.g., the energy per particle approach a value $\hbar^2n^{2/3}/m$ times an universal many-body constant. Calculations based upon an approximate Jastrow wave function can quantitatively describe recent measurements of trapped Bose and Fermi atoms near Feshbach resonances. The pairing gap between attractive fermions also scales as $\Delta\sim\hbar^2n^{2/3}/m$ near Feshbach resonances and is a large fraction of the Fermi energy - promising for observing BCS superfluidity in traps. Pairing undergoes several transitions depending on interaction strength and the number of particles in the trap and can also be compared to pairing in nuclei.