费米子对，从表面到体相
Fermionic pairs, from the surface to the bulk
AI总结：
研究有限可调的少数费米子原子系统中对关联，通过成像以单粒子分辨率和全计数统计观察，发现禁闭和壳层结构影响配对，解析了对的形成及特征变化，提供微观视角并联系不同体系的配对现象。
AI中文摘要：
费米子配对是各种不同物质形态中集体量子现象的基础。在超冷费米气体等扩展系统中，配对通常通过BCS - BEC交叉来理解，其中对的大小从大的、重叠的库珀对演变为紧密结合的二聚体。然而，在原子核、超导颗粒和量子点等有限系统中，相同的配对趋势与禁闭、壳层填充和空间不均匀性相互竞争，使得对的微观结构更难探究。在此，我们以单粒子分辨率和全计数统计对少数费米子原子的有限可调系统中的对关联进行成像。我们观察到禁闭和壳层结构在实空间中重新组织配对：在弱相互作用、禁闭主导的区域，闭壳层构型抑制高密度陷阱中心的关联。配对主要在低密度表面观察到。然而，开壳层系统支持更强的中心配对。对于小得惊人的系统，增加相互作用强度或粒子数会在陷阱中心恢复局部类似体相的库珀对分布型，而边缘保留二聚体样关联。通过解析对在哪里形成以及它们的特征如何从局域二聚体变为重叠库珀对，我们的测量提供了有限费米子物质中配对的微观视角，并将介观冷原子的物理与原子核和超导纳米结构中的配对现象联系起来。
英文摘要：
Fermion pairing underlies collective quantum phenomena across widely different forms of matter. In extended systems such as ultracold Fermi gases, pairing is commonly understood through the BCS--BEC crossover, where the pair size evolves from large, overlapping Cooper pairs to tightly bound dimers. In finite systems such as atomic nuclei, superconducting grains and quantum dots, however, the same pairing tendency competes with confinement, shell filling and spatial inhomogeneity, making the microscopic structure of pairs much harder to access. Here, we image pair correlations in a finite, tunable system of few fermionic atoms with single-particle resolution and full counting statistics. We observe that confinement and shell structure re-organize pairing in real space: In the weakly interacting, confinement-dominated regime, closed-shell configurations suppress correlations in the high-density trap center. Pairing is mainly observed toward the low-density surface. Open-shell systems, however, support substantially stronger central pairing. Already for surprisingly small systems, increasing either interaction strength or particle number restores a locally bulk-like Cooper-pair profile in the trap center, whereas the edge retains dimer-like correlations. By resolving where pairs form and how their character changes from localized dimers to overlapping Cooper pairs, our measurements provide a microscopic view of pairing in finite fermionic matter and connect the physics of mesoscopic cold atoms to pairing phenomena in nuclei and superconducting nanostructures.
