Theory of trapped superfluid fermi gases

自从1995年在激光冷却的碱性原子中戏剧性地发现了玻色-爱因斯坦凝聚(BEC)(经过几十年的努力)以来，关于超冷原子和超冷物质性质的研究已经在世界范围内爆发。BEC涉及宏观数量的原子占据相同的单粒子量子态，这导致了超流体性质(持续电流、量子化涡旋等)。它们是在超流体He和超导体中发现的类似物。他说，我目前的研究是在费什巴赫共振存在的情况下处理囚禁的费米气体，这种共振允许人们“调节”S波散射长度的大小和符号(它完全描述了超冷温度下的原子间相互作用)。因为在这些费米气体中可以使相互作用非常大，所以人们可以在有限的温度下探测两种流体的流体动力学。1941年，朗道首先在超流液体的背景下进行了研究。朗道的双流体方程应该描述整个BCS-BEC交叉(从库珀对的BCS凝聚体到真实分子的BEC)的动力学。我的工作涉及到详细研究双流体集体振荡(类似于均匀玻色超流体中的第一和第二声音)。具有费什巴赫共振的超流费米气体使我们第一次能够探索碰撞起关键作用的囚禁量子气体的局部平衡区。即使密度仍然非常小。对囚禁费米超流体气体中双流体行为的实验观察将完全类似于1938年对液氦超流动性的历史观察，尽管由于热力学的不同，量子气体中的详细性质将截然不同。

Since the dramatic discovery in 1995 of Bose-Einstein condensation (BEC) in laser-cooled alkali atoms (after decades of effort), there has been a worldwide explosion of research on the properties of ultracold atoms and ultracold matter.  BEC involves a macroscopic number of atoms occupying the same single-particle quantum state, which results in superfluid properties (persistent currents, quantized vortices, etc.) which are the analogue of those found in superfluid He and superconductors.        My current research deals with trapped Fermi gases in the presence of a Feshbach resonance, which allows one to "tune" the size and sign of the s-wave scattering length (which completely describes the interatomic interaction at ultracold temperature).  Because the interaction can be made very large in these Fermi gases, one can probe the two-fluid hydrodynamics at finite temperatures, first studied by Landau in 1941 in the context of superfluid liquid He.  The Landau two-fluid equations should describe the dynamics across the entire BCS-BEC crossover (going from a BCS condensate of Cooper pairs to a BEC of real molecules).  My work involves a detailed study of the two-fluid collective oscillations (the analogue of first and second sound in a uniform Bose superfluid).  Superfluid Fermi gases with a Feshbach resonance allow us for the first time to probe the local equilibrium region of trapped quantum gases where collisions play a crucial role, even though the density is still extremely small.  Experimental observation of two-fluid behaviour in trapped Fermi superfluid gases would be the complete analogue of the historic observations in 1938 of superfluidity in liquid Helium, although the detailed properties will be quite different in quantum gases because of the different thermodynamics.