Collision of two spin polarized fermionic clouds

TL;DR

This paper investigates the collision dynamics of two spin-polarized Fermi clouds in a harmonic trap, revealing three behavioral regimes and demonstrating the role of collisions in nonlinear mode coupling.

Contribution

It introduces a semiclassical collisional approach to reproduce experimental phenomena and explores the nonlinear coupling between collective modes in quantum gases.

Findings

Weak interactions allow clouds to pass through each other

Increased interactions lead to exponential approach

Strong interactions cause multiple bounces and mode coupling

Abstract

We study the collision of two spin polarized Fermi clouds in a harmonic trap using a simulation of the Boltzmann equation. As observed in recent experiments we find three distinct regimes of behavior. For weak interactions the clouds pass through each other. If interactions are increased they approach each other exponentially and for strong interactions they bounce off each other several times. We thereby demonstrate that all these phenomena can be reproduced using a semiclassical collisional approach and that these changes in behavior are associated with an increasing collision rate. We then show that the oscillation of the clouds in the bounce regime is an example of an unusual case in quantum gases: a nonlinear coupling between collective modes, namely the spin dipole mode and the axial breathing mode which is enforced by collisions. We also determine the frequency of the bounce as a function of the final temperature of the equilibrated system.