Rührig Jahn, Bäuerle Tobias, Griesmaier Axel, Pfau Tilman
Opt Express. 2015 Mar 9;23(5):5596-606. doi: 10.1364/OE.23.005596.
Demagnetization cooling utilizes dipolar relaxations that couple the internal degree of freedom (spin) to the external (angular momentum) in order to cool an atomic cloud efficiently. Optical pumping into a dark state constantly recycles the atoms that were thermally excited to higher spin states. The net energy taken away by a single photon is very favorable since the lost energy per atom is the Zeeman energy rather than the recoil energy. As the density of the atomic sample rises the presence of the photons leads to limiting processes. In our previous publication [Volchkov et al. (2014)] we have shown that light-assisted collisions are such an important limiting process. In this paper we suppress light-assisted collisions by detuning the optical pumping light such that the Condon point coincides with the first node of the ground state wave function of two colliding atoms. This leads to an increased cooling efficiency χ ≥ 17 as well as to increased maximum densities of n ≈ 1 · 10(20) m(-3). However, due to the high number of involved molecular states the net suppression is not strong enough to reach quantum degeneracy.
退磁冷却利用偶极弛豫将内部自由度（自旋）与外部（角动量）耦合，从而有效地冷却原子云。光泵浦到暗态可不断循环热激发到更高自旋态的原子。单个光子带走的净能量非常有利，因为每个原子损失的能量是塞曼能量而非反冲能量。随着原子样品密度的增加，光子的存在会导致限制过程。在我们之前的出版物[Volchkov等人（2014年）]中，我们表明光辅助碰撞就是这样一个重要的限制过程。在本文中，我们通过使光泵浦光失谐来抑制光辅助碰撞，使得康登点与两个碰撞原子基态波函数的第一个节点重合。这导致冷却效率提高χ≥17，以及最大密度增加到n≈1·10²⁰ m⁻³。然而，由于涉及的分子态数量众多，净抑制作用不够强，无法达到量子简并。
