费米气体的配对冷却
Pairing based cooling of Fermi gases
摘要：
提出了一种基于对效应的费米气体冷却方法。考虑费米子的三组分（标号1，2，3）混合物，其中组分1和2相互作用，例如形成对，而组分3处于正常状态。为了冷却，部件2和3通过电磁场耦合。由于准粒子在成对态和正常态中的分布不同，耦合导致正常态的冷却，即使最初是$T_{paired}\geq T_{normal}$（符号$T_S\geq T_N$）。冷却效率由对能和耦合场的线宽给出。不需要超流性：任何类型的配对，或其他产生适当谱密度的现象，都是足够的。原则上，配对状态也可以被冷却，但这需要$T_N<T_S$。该方法在概念上类似于基于超导体-正常金属（SN）隧道结的冷却。主要的区别来自于场-物质耦合情况下的精确动量守恒与固态隧穿过程中的动量不守恒。此外，放宽隧道中的能量守恒要求的过程的作用，例如外部储层的热波动，现在由场的线宽发挥作用。所提出的方法应该是实验上可行的，由于其密切联系的超冷气体的RF光谱，这是已经在使用。
英文摘要：
We propose a pairing-based method for cooling an atomic Fermi gas. A three component (labels 1, 2, 3) mixture of Fermions is considered where the components 1 and 2 interact and, for instance, form pairs whereas the component 3 is in the normal state. For cooling, the components 2 and 3 are coupled by an electromagnetic field. Since the quasiparticle distributions in the paired and in the normal states are different, the coupling leads to cooling of the normal state even when initially $T_{paired}\geq T_{normal}$ (notation $T_S\geq T_N$). The cooling efficiency is given by the pairing energy and by the linewidth of the coupling field. No superfluidity is required: any type of pairing, or other phenomenon that produces a suitable spectral density, is sufficient. In principle, the paired state could be cooled as well but this requires $T_N<T_S$. The method has a conceptual analogy to cooling based on superconductor -- normal metal (SN) tunneling junctions. Main differences arise from the exact momentum conservation in the case of the field-matter coupling vs. non-conservation of momentum in the solid state tunneling process. Moreover, the role of processes that relax the energy conservation requirement in the tunneling, e.g. thermal fluctuations of an external reservoir, is now played by the linewidth of the field. The proposed method should be experimentally feasible due to its close connection to RF-spectroscopy of ultracold gases which is already in use.
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