标题： 旋转费米子超流体的角动量通过萨格纳克声子干涉仪 显示英文标题

标题： Angular momentum of rotating fermionic superfluids by Sagnac phonon interferometry

摘要： 费米子多体系统为研究相互作用如何驱动集体量子行为的出现提供了无与伦比的场所，例如宏观相干性和超流性。 这些现象的核心是库珀对的形成，这是两个费米子的关联态，它们作为复合玻色子在临界温度以下凝聚。 然而，与基本玻色子不同，这些对保留了由底层费米子关联设定的内部结构，这对于理解所谓的玻色-爱因斯坦凝聚（BEC）到巴丁-库珀-施里弗（BCS）交叉区域中超流性质至关重要——这是强关联费米子物质的基石。 在这里，我们利用光学萨格纳克效应的声学类比，揭示了费米子凝聚在BEC-BCS交叉区域中的复合特性。 我们通过相干激发环形费米子超流体中两个相反传播的长波长声子，实现了原位环形干涉仪。 当在超流环中可控地注入一个量子化的超流时，顺时针和逆时针声模之间的频率简并被打破，导致可测量的多普勒频移，使我们能够探测超流中的基本循环量子以及每个粒子携带的角动量。 我们的观测直接表明，超流循环以$h/2m$为单位量化，其中$m$是组成粒子的质量，这与玻色子凝聚中$h/m$是相关循环量子的情况形成鲜明对比。 此外，通过在可调温度下操作我们的干涉仪，我们测量了单位费米气体中超流的热耗竭，证明了声子干涉测量是一种研究强关联量子系统基本性质的强大技术。 显示英文摘要

摘要： Fermionic many-body systems provide an unrivaled arena to investigate how interactions drive the emergence of collective quantum behavior, such as macroscopic coherence and superfluidity. Central to these phenomena is the formation of Cooper pairs, correlated states of two fermions that behave as composite bosons and condense below a critical temperature. However, unlike elementary bosons, these pairs retain their internal structure set by underlying fermionic correlations, essential for understanding superfluid properties throughout the so-called Bose-Einstein condensate (BEC) to Bardeen-Cooper-Schrieffer (BCS) crossover-- a cornerstone of strongly correlated fermionic matter. Here, we harness a sonic analog of the optical Sagnac effect to disclose the composite nature of fermionic condensates across the BEC-BCS crossover. We realize an in-situ loop interferometer by coherently exciting two counter-propagating long-wavelength phonons of an annular fermionic superfluid with tuneable interparticle interactions. The frequency degeneracy between clock- and anticlock-wise sound modes is lifted upon controllably injecting a quantized supercurrent in the superfluid ring, resulting in a measurable Doppler shift that enables us to probe the elementary quantum of circulation and the angular momentum carried by each particle in the fermionic fluid. Our observations directly reveal that the superflow circulation is quantized in terms of $h/2m$, where $m$ is the mass of the constituents, in striking contrast to bosonic condensates where $h/m$ is the relevant circulation quantum. Further, by operating our interferometer at tunable temperature, we measure the thermal depletion of the superfluid in the unitary Fermi gas, demonstrating phonon interferometry as a powerful technique for probing fundamental properties of strongly-correlated quantum systems.