Cold Fermi-gas with long range interaction in a harmonic trap

TL;DR

This paper extends the collective field theory of the spin-Calogero model to include harmonic trapping, providing analytical results for equilibrium and dynamic density profiles of one-dimensional long-range interacting fermions.

Contribution

It introduces an analytic approach to describe equilibrium and non-equilibrium dynamics of trapped long-range interacting fermions using a gradientless hydrodynamic approximation.

Findings

Equilibrium density profiles change with interaction strength.

Analytical solutions for spin and charge dynamics are obtained.

Time evolution of non-equilibrium profiles can be described as single-particle phase-space trajectories.

Abstract

We study equilibrium density and spin density profiles for a model of cold one-dimensional spin 1/2 fermions interacting via inverse square interaction and exchange in an external harmonic trap. This model is the well-known spin-Calogero model (sCM) and its fully nonlinear collective field theory description is known. We extend the field theory description to the presence of an external harmonic trap and obtain analytic results for statics and dynamics of the system. For instance, we find how the equilibrium density profile changes upon tuning the interaction strength. The results we obtain for equilibrium configurations are very similar to the ones obtained recently by Ma and Yang [1] for a model of fermions with short ranged interactions. Our main approximation is the neglect of the terms of higher order in spatial derivatives in equations of motion - gradientless approximation [2]. Within this approximation the hydrodynamic equations of motion can be written as a set of decoupled forced Riemann-Hopf equations for the dressed Fermi momenta of the model. This enables us to write analytical solutions for the dynamics of spin and charge. We describe the time evolution of the charge density when an initial non-equilibrium profile is created by cooling the gas with an additional potential in place and then suddenly removing the potential. We present our results as a simple "single-particle" evolution in the phase-space reminiscing a similar description of the dynamics of non-interacting one-dimensional fermions.