Few-body Phenomena in a Degenerate Fermi Gas

我们将研究最近才出现的一个新领域——超冷原子。这些系统是由极低温度（百万分之一开尔文数量级）的原子气体储存在超高真空中，并表现出某些量子力学特性。在过去的几年里，实验学家已经能够创建和研究一些原子与其他原子属于不同种类的系统（例如，它们具有不同的内部状态，称为自旋）。这些原子可以被认为由于它们与背景原子（大多数物种）的相互作用而影响了它们的运动特性。我们可以打个比方：想象不同的原子就像在粘性流体（如水）中运动的圆球（如台球）。由于流体和球体之间的相互作用（阻力），我们可以说球体的质量增加了，因为它们现在有了更多的惯性。事实证明，在物理学的许多领域（凝聚态物质、粒子物理和其他领域），这种思考问题的方式非常有用，并导致许多见解。当我们将几个不同的原子引入这个背景中时，不仅它们的惯性会改变（我们说它们的有效质量改变了），而且它们行为的其他方面也会改变。例如，它们相互碰撞的方式，或者彼此形成分子的方式。因此，我们建议广泛地研究这些原子如何相互碰撞以及它们之间的相互作用。ii)这些原子如何在介质中传播（例如它们的惯性，介质对原子运动的减速效应，称为阻尼）。(3)原子在介质存在下（即在真空中）能形成什么样的分子和化合物？iv)如何最好地通过实验检测和测量这些影响，使用什么技术以及在数据中寻找什么。除了对研究原子的兴趣之外，还有一个更广泛的兴趣：在我们的具体例子中，背景气体是一种被称为简并费米气体的气体。这个系统是许多系统的模型，从金属中的电子到中子星中的核物质，因此，我们提出研究的现象在这些其他系统中都有相似的类似物。

We will study a new area which has appeared only recently in the field of ultracold atoms. These systems are composed of gases of atoms at very low temperature (on the order of a millionth of a degree Kelvin) stored in ultrahigh vacuum which exhibit certain quantum mechanical properties.In the past couple of years experimentalists have been able to create and study systems where a few of the atoms are of different species from the others (e.g. they have a different internal state known as spin ). These atoms can be thought of as having their motional properties affected due to their interaction with the background atoms (the majority species). We can use an analogy here: imagine that the different atoms are like round spheres (such as billiard balls) moving through a viscous fluid (e.g. water). Because of the interaction between the fluid and the sphere (the drag force), we might say that the spheres have increased their mass since they have more inertia now. It turns out that in many areas of physics (condensed matter, particle physics and others) this way of thinking about the problem is very useful and leads to many insights.When we introduce the few different atoms into this background, not only will their inertia change (we say that their effective mass has changed), but also other aspects of their behaviour. For example, the way they collide with each other, or form molecules with each other.Very broadly we propose to study thereforei) How these atoms collide with each other and their interactions.ii) How these atoms propagate in the medium (e.g. their inertia, the slowing down effect of the medium on the motion of the atoms, known as damping).iii) What kinds of molecules and compounds can the atoms form in the presence of the medium which they could not before (i.e. in vacuum).iv) How best to detect and measure these effects experimentally, what techniques to use and what to look for in the data.Beyond the interest in studying atoms there is a wider one: in our specific case the background gas is of a type known as a degenerate Fermi gas . This system is a model for many systems, from electrons in metals to nuclear matter in neutron stars and therefore, the phenomena that we propose to study has close analogs in each of these other systems.