Determination of the fermion pair size in a resonantly interacting superfluid.

摘要: Fermionic superfluidity requires the formation of particle pairs, size which varies depending on system. Many properties superfluid depend pair relative to inter-particle spacing. For example, conventional superconductors comprise a loosely bound, large Cooper pairs electrons, while Bose-Einstein condensates contain tightly bound molecules. The microscopic fermion can be probed with radio-frequency spectroscopy. However, previous results have been difficult interpret due strong final-state interactions that were not well understood. Schunck et al. realize spin mixture in an ultracold gas lithium atoms such negligible influence. They find spectroscopic is smaller than These are smallest yet observed for fermionic superfluids. In related experiment, Jin al use technique called photoemission spectroscopy study excitations strongly interacting potassium atoms. Such studies interest because physics high transition-temperature superconductors, fully Microscopic But work was interactions, A atomic influence realized, and it found from femtometre scale neutron stars nuclei micrometre superconductors. interparticle This expressed ‘BCS–BEC crossover’ theories1,2,3, describing crossover Bardeen–Cooper–Schrieffer (BCS)-type Bose–Einstein (BECs) has realized gases where high-temperature observed4,5. using work6,7,8 owing Here we present dissociation spectra reveal underlying pairing correlations. allows us determine resonantly 20 per cent so far superfluids, highlighting importance small at critical temperatures9. We also identified transitions molecular states many-body case interactions.