Abstract We investigate nonequilibrium steady states in an isolated system of few ultracold cesium atoms (Cs). Numerically and experimentally, we study the dynamics and fluctuations of the extracted position distributions and find the formation of nonthermal steady states for absent interactions. Atomic collisions in the s-wave regime, however, ensue thermalization of the few-particle system. We present numerical simulations of the microscopic equations of motion with a simple representation of the s-wave scattering events. Based on these simulations, a parameter range is identified, where the interaction between few atoms is sufficiently strong to thermalize the nonequilibrium steady state on experimentally accessible time scales, which can be traced by monitoring the atomic position distribution. Furthermore, the total energy distribution, which is also accessible experimentally, is found to be a powerful tool to observe the emergence of a thermal state. Our work provides a pathway for future experiments investigating the effect interactions in few-particle systems and underlines the role of fluctuations in investigating few-particle systems.

中文翻译：

---

少原子系统中的热化和非平衡稳态

摘要 我们研究了少数超冷铯原子 (Cs) 的孤立系统中的非平衡稳态。在数值和实验上，我们研究了提取的位置分布的动力学和波动，并找到了不存在相互作用的非热稳态的形成。然而，s 波状态下的原子碰撞会导致少粒子系统的热化。我们用 s 波散射事件的简单表示来呈现微观运动方程的数值模拟。基于这些模拟，确定了一个参数范围，其中少数原子之间的相互作用足够强，可以在实验可访问的时间尺度上热化非平衡稳态，这可以通过监测原子位置分布来追踪。此外，总能量分布，这也可以通过实验获得，被发现是观察热状态出现的有力工具。我们的工作为未来研究少粒子系统中的效应相互作用的实验提供了途径，并强调了波动在研究少粒子系统中的作用。