Cooling phonon modes of a Bose condensate with uniform few body losses

TL;DR

This paper analyzes how uniform few-body losses induce cooling in Bose condensates by adiabatically reducing phonon mode occupations, applicable to various geometries and interaction regimes, revealing a temperature decrease proportional to the sound energy scale.

Contribution

It provides a general theoretical framework for understanding loss-induced cooling in Bose gases, including effects of interactions and confinement, extending previous models.

Findings

Temperature decreases proportionally to mc^2 at large times

Derived asymptotic ratios of temperature to energy scale for different geometries

Applicable to any loss process proportional to density power with uniform spatial profile

Abstract

We present a general analysis of the cooling produced by losses on condensates or quasi-condensates. We study how the occupations of the collective phonon modes evolve in time, assuming that the loss process is slow enough so that each mode adiabatically follows the decrease of the mean density. The theory is valid for any loss process whose rate is proportional to the $j$th power of the density, but otherwise spatially uniform. We cover both homogeneous gases and systems confined in a smooth potential. For a low-dimensional gas, we can take into account the modified equation of state due to the broadening of the cloud width along the tightly confined directions, which occurs for large interactions. We find that at large times, the temperature decreases proportionally to the energy scale $mc^2$, where $m$ is the mass of the particles and $c$ the sound velocity. We compute the asymptotic ratio of these two quantities for different limiting cases: a homogeneous gas in any dimension and a one-dimensional gas in a harmonic trap.