Bloch I, Hansch TW, Esslinger T
Sektion Physik, Ludwig-Maximilians-Universitat, Munich, Germany.
Nature. 2000 Jan 13;403(6766):166-70. doi: 10.1038/35003132.
The experimental realization of Bose-Einstein condensates of dilute gases has allowed investigations of fundamental concepts in quantum mechanics at ultra-low temperatures, such as wave-like behaviour and interference phenomena. The formation of an interference pattern depends fundamentally on the phase coherence of a system; the latter may be quantified by the spatial correlation function. Phase coherence over a long range is the essential factor underlying Bose-Einstein condensation and related macroscopic quantum phenomena, such as superconductivity and superfluidity. Here we report a direct measurement of the phase coherence properties of a weakly interacting Bose gas of rubidium atoms. Effectively, we create a double slit for magnetically trapped atoms using a radio wave field with two frequency components. The correlation function of the system is determined by evaluating the interference pattern of two matter waves originating from the spatially separated 'slit' regions of the trapped gas. Above the critical temperature for Bose-Einstein condensation, the correlation function shows a rapid gaussian decay, as expected for a thermal gas. Below the critical temperature, the correlation function has a different shape: a slow decay towards a plateau is observed, indicating the long-range phase coherence of the condensate fraction.
稀薄气体玻色 - 爱因斯坦凝聚体的实验实现使得在超低温下对量子力学中的基本概念进行研究成为可能，比如波动行为和干涉现象。干涉图样的形成从根本上取决于系统的相位相干性；后者可以通过空间关联函数来量化。长程的相位相干性是玻色 - 爱因斯坦凝聚以及相关宏观量子现象（如超导和超流）背后的关键因素。在此，我们报告了对铷原子弱相互作用玻色气体相位相干特性的直接测量。实际上，我们利用具有两个频率分量的射频场为磁阱中的原子创建了一个双缝。通过评估源自捕获气体空间分离“缝”区域的两束物质波的干涉图样来确定系统的关联函数。在玻色 - 爱因斯坦凝聚的临界温度之上，关联函数呈现出快速的高斯衰减，这正如热气体所预期的那样。在临界温度之下，关联函数具有不同的形状：观察到朝着一个平台缓慢衰减，这表明凝聚部分具有长程相位相干性。
