Stabilization of the number of Bose-Einstein condensed atoms in evaporative cooling via three-body recombination loss

TL;DR

This paper models the evaporative cooling process of trapped rubidium atoms, revealing that three-body recombination loss stabilizes the final number of Bose-Einstein condensed atoms despite experimental fluctuations.

Contribution

It provides a quantitative analysis showing how three-body recombination loss stabilizes the condensate number during evaporative cooling.

Findings

Three-body recombination causes significant atom loss near quantum degeneracy.

The final condensate number becomes insensitive to initial conditions due to nonlinear loss.

Stabilization occurs despite variations in initial atom number, temperature, and magnetic bias.

Abstract

The dynamics of evaporative cooling of magnetically trapped $^{87}$Rb atoms is studied on the basis of the quantum kinetic theory of a Bose gas. We carried out the quantitative calculations of the time evolution of conventional evaporative cooling where the frequency of the radio-frequency magnetic field is swept exponentially. This "exponential-sweep cooling" is known to become inefficient at the final stage of the cooling process due to a serious three-body recombination loss. We precisely examine how the growth of a Bose-Einstein condensate depends on the experimental parameters of evaporative cooling, such as the initial number of trapped atoms, the initial temperature, and the bias field of a magnetic trap. It is shown that three-body recombination drastically depletes the trapped $^{87}$Rb atoms as the system approaches the quantum degenerate region and the number of condensed atoms finally becomes insensitive to these experimental parameters. This result indicates that the final number of condensed atoms is well stabilized by a large nonlinear three-body loss against the fluctuations of experimental conditions in evaporative cooling.