Are ultracold molecular collisions sticky? [dataset]

Understanding and controlling collisions is crucial to the burgeoning field of ultracold molecules. All experiments so far have observed fast loss of molecules from the trap. However, the dominant mechanism for collisional loss is not well understood when there are no allowed 2-body loss processes. Here we experimentally investigate collisional losses of nonreactive ultracold RbCs molecules, and compare our findings with the sticky collision hypothesis that pairs of molecules form long-lived collision complexes. We demonstrate that loss of molecules occupying their rotational and hyperfine ground state is best described by second-order rate equations, consistent with the expectation for complex-mediated collisions, but that the rate is lower than the limit of universal loss. The loss is insensitive to magnetic field but increases for excited rotational states. We demonstrate that dipolar effects lead to significantly faster loss for an incoherent mixture of rotational states.

理解并调控碰撞过程对于蓬勃发展的超冷分子领域至关重要。迄今为止，所有实验均观察到分子从阱中快速损失的现象。然而，在不存在允许的两体损失过程时，碰撞损失的主导机制尚未得到充分理解。本文通过实验研究了非反应性超冷铷铯（RbCs）分子的碰撞损失，并将观测结果与黏滞碰撞假说（即分子对形成长寿命碰撞复合物）进行了对比。我们发现，处于转动和超精细基态的分子损失可用二阶速率方程最佳描述，这与复合物介导碰撞的预期一致，但该速率低于普适损耗的极限。这种损失对磁场不敏感，但在激发转动态下会加剧。我们还发现，偶极效应会导致转动态非相干混合物的损失速率显著加快。