标题： 玻色气体能被饱和吗？ 显示英文标题

标题： Can a Bose gas be saturated?

摘要： 玻色-爱因斯坦凝聚在物质不同状态之间的相变中是独特的，因为它即使在粒子之间没有相互作用的情况下也会发生。 在爱因斯坦的理想气体教科书图景中，纯粹的统计论证设定了占据系统激发态的粒子数的上限，凝聚是由这种量子蒸气的饱和驱动的。 稀薄的超冷原子气体被公认为实现了接近其纯粹统计形式的玻色-爱因斯坦凝聚。 在这里，我们使用一种钾（39K）原子的超冷气体来仔细审视这一观点，其中相互作用的强度可以通过费什巴赫散射共振进行调节。 我们首先表明，在典型的实验条件下，部分凝聚的原子气体与教科书中的饱和蒸气概念有显著偏差。 然后，我们通过在不同相互作用强度和温度下的测量来外推到无相互作用极限，并证明在这种极限下，玻色气体的行为与饱和图景一致。 最后，我们通过使用另一种原子种类87Rb的额外测量来提供我们观察结果的普遍性证据。 我们的结果表明了一种表征不同物理系统中凝聚现象的新方法。 显示英文摘要

摘要： Bose-Einstein condensation is unique among phase transitions between different states of matter in the sense that it occurs even in the absence of interactions between particles. In Einstein's textbook picture of an ideal gas, purely statistical arguments set an upper bound on the number of particles occupying the excited states of the system, and condensation is driven by this saturation of the quantum vapour. Dilute ultracold atomic gases are celebrated as a realisation of Bose-Einstein condensation in close to its purely statistical form. Here we scrutinise this point of view using an ultracold gas of potassium (39K) atoms, in which the strength of interactions can be tuned via a Feshbach scattering resonance. We first show that under typical experi-mental conditions a partially condensed atomic gas strongly deviates from the textbook concept of a saturated vapour. We then use measurements at a range of interaction strengths and temperatures to extrapolate to the non-interacting limit, and prove that in this limit the behaviour of a Bose gas is consistent with the saturation picture. Finally, we provide evidence for the universality of our observations through additional measurements with a different atomic species, 87Rb. Our results suggest a new way of characterising condensation phenomena in different physical systems.