Cooling a Bose Gas by Three-Body Losses

We report the demonstration of cooling by three-body losses in a Bose gas. We use a harmonically confined one-dimensional (1D) Bose gas in the quasicondensate regime and, as the atom number decreases under the effect of three-body losses, the temperature $T$ drops up to a factor of 4. The ratio $k_{B}T/(m{c}^2)$ stays close to 0.64, where $m$ is the atomic mass and $c$ the speed of sound in the trap center. The dimensionless 1D interaction parameter $\gamma$, evaluated at the trap center, spans more than 2 orders of magnitudes over the different sets of data. We present a theoretical analysis for a homogeneous 1D gas in the quasicondensate regime, which predicts that the ratio $k_{B}T/(m{c}^2)$ converges towards 0.6 under the effect of three-body losses. More sophisticated theoretical predictions that take into account the longitudinal harmonic confinement and transverse effects are in agreement within 30% with experimental data.

Figure 1

Peak density, in log scale, versus the waiting time $t$, for the five different data sets. Solid lines are ab initio calculations of the effect of three-body losses, for initial peak densities equal to that of the experimental data.

Figure 2

Evolution of the temperature for the five data sets (same color code and symbols as in Fig. 1). Inset: density ripples power spectrum corresponding to the encircled point, with the fit in solid line yielding the temperature.

Figure 3

Evolution of the ratio $k_{B}T/(m{c}_p^2)$, in the course of the three-body loss process, for the five data sets (same color code and symbols as in Fig. 1). The temperature decreases with $c_p^2$, which is approximately proportional to $n_p$. Solid (respectively, dashed) lines: asymptotic ratio for a 1D homogeneous (respectively, harmonically confined) gas. Dotted lines: numerical calculation, that takes into account the transverse swelling, for two different initial situations close to that of experimental data.

Figure 4

The data collapse on the line $\tilde{\gamma }{\tilde{t}}_{YY}=0.7$. The lower right corner corresponds to the strongly interacting Tonks-Girardeau regime. The data sets and color (symbols) codes are the same as in all other figures.