Radio-frequency spectroscopic measurement for pairing gap in an ultracold Fermi gas

The study of ultracold Fermi gases has exploded a variety of experimental and theoretical research since the achievement of degenerate quantum gases in the lab, which expands the research range over atomic physics, condensed matter physics, astrophysics and particle physics. Using the Feshbach resonance, one can tune the attractive two-body interaction from weak to strong and thereby make a smooth crossover from the BCS superfluid of cooper pairs to the Bose Einstein condensate of bound molecules. In this crossover regime, the pairing effect plays a significant role in interpreting the interaction mechanism. Whenever the localized or delocalized pairing occurs at sufficiently low temperature, the single-particle energy will shift with respect to free atoms, due to the two-body or many-body interaction. Measuring the pairing gap can improve the understanding of the thermodynamics and hydrodynamics of the phase transition from the pseudogap to the superfluid, which will make an analogue to the high-temperature superconductivity in condensed matter. In this work, we will give a brief introduction to a novel radio-frequency (RF) spectroscopic measurement for pairing gap in an ultracold Fermi gas, which is currently widely used on the ultracold atomic table in the lab. In different interaction regimes of the BEC-BCS crossover, ultracold atoms are excited with a RF pulse and the characteristic behavior can be extracted from the spectrum.