Optimization of collisional Feshbach cooling of an ultracold nondegenerate gas

TL;DR

This paper presents an optimized collision-induced cooling method for ultracold nondegenerate gases using Feshbach resonances, with analytical and numerical validation, improving phase-space density without background losses.

Contribution

It introduces an analytical framework for tuning Feshbach resonance energy to optimize cooling, validated by simulations, and considers realistic loss mechanisms.

Findings

Optimal resonance energy linearly follows temperature during cooling.

Background losses do not affect the optimal tuning.

Non-resonant two-body losses favor lower initial resonance energy.

Abstract

We optimize a collision-induced cooling process for ultracold atoms in the nondegenerate regime. It makes use of a Feshbach resonance, instead of rf radiation in evaporative cooling, to selectively expel hot atoms from a trap. Using functional minimization we analytically show that for the optimal cooling process the resonance energy must be tuned such that it linearly follows the temperature. Here, optimal cooling is defined as maximizing the phase-space density after a fixed cooling duration. The analytical results are confirmed by numerical Monte-Carlo simulations. In order to simulate more realistic experimental conditions, we show that background losses do not change our conclusions, while additional non-resonant two-body losses make a lower initial resonance energy with non-linear dependence on temperature preferable.