Evaporative Cooling of Trapped Atoms

Kendall B. Davis, M.‐O. Mewes, Wolfgang Ketterle

Xiaolong Yuan, Jiachen Yu, H. Li +4 more

In this paper, to investigate how atoms evaporate and cool in microgravity environments of the space station, we have developed the dynamic equation for evaporative cooling of trapped atoms and obtained the analytical expression of atomic temperature with respect to trapping laser parameters and gravitational acceleration. In our model, the evaporation of atoms is equivalent to applying a damping force to the trapped atoms, and the evaporative cooling process of trapped atoms is comprehended as the damped oscillation of trapped atoms in the optical dipole traps. By introducing the gravity in our model, we obtained the analytical model of temperature variation with gravity after cooling, and the theoretical results agree well with the evaporation experiment of rubidium-87 atoms on the ground. Our theoretical results show that, compared with the atomic evaporative cooling experiment on the ground, the microgravity environment of the space station can achieve cooler atomic gases when the losses of atoms, such as the one-body loss caused by background-gas collisions and the three-body recombination loss caused by interatomic inelastic collisions, can be ignored.

Emmanuel Mandonnet, Anna Minguzzi, Ralph Dum +3 more

Hongyu Ma, Cheng Hua-Dong, Wang Yu-Zhu +1 more

This paper presents an experimental demonstration of light-induced evaporative cooling in a magneto-optical trap. An additional laser is used to interact with atoms at the edge of the atomic cloud in the trap. These atoms get an additional force and evaporated away from the trap by both the magnetic field and laser fields. The remaining atoms have lower kinetic energy and thus are cooled. It reports the measurements on the temperature and atomic number after the evaporative cooling with different parameters including the distance between the laser and the centre of the atomic cloud, the detuning, the intensity. The results show that the light-induced evaporative cooling is a way to generate an ultra-cold atom source.

Yoshiro Takahashi

Evaporative cooling of ultracold Yb atoms near the quantum-degenerate regime was experimentally studied. Three bosons of 170Yb, 172Yb, 176Yb and two fermions of 171Yb and 173Yb were evaporatively cooled in a crossed far-off resonant trap (FORT). We observed that 170Yb and 172Yb were not concentrated into the crossed region. We found that, in the cases of 176Yb atoms, atoms were concentrated well into the crossed region. The following evaporative cooling in the crossed region, however, did not work well. We performed the simultaneous trapping and sympathetic cooling in the crossed FORT by use of 172Yb-174Yb, 174Yb-176Yb, 172Yb-176Yb, and 171Yb-174Yb pairs. We observed that evaporative cooling worked well. This result shows that we succeeded in the enhancement of the atom collision rate. Especially, by use of 174Yb-176Yb mixture, we obtained cold 176Yb whose phase space density was 0.02. We observed a large atom loss, which limited the further sympathetic evaporative cooling. We also evaporatively cooled 174Yb in a 1D optical lattice. Evaporative cooling worked very well because the atoms were initially trapped at a high density. After evaporative cooling, we obtained very cold atoms, and T/TF was estimated to be 1.2.

Carl Wieman