Measuring the angular momentum of Fermi superfluids

We are pleased to announce the publication of our latest work in Nature Physics, where we demonstrate a new way to investigate the quantum properties of strongly interacting fermionic superfluids. By combining ultracold atoms with a novel phonon interferometry technique, we realized a sonic analogue of the optical Sagnac interferometer inside a ring-shaped superfluid, allowing us to precisely detect quantized supercurrents and directly probe how pairs of fermions behave collectively across different interaction regimes.

Our measurements reveal that the circulation of the superfluid is quantized in units of h/2m, providing direct evidence that the superfluid flow is carried by paired fermions rather than individual particles. The results offer new insight into the microscopic origin of superfluidity, enable access to the superfluid fraction of a unitary Fermi gas, and establish phonon interferometry as a powerful new tool for studying strongly correlated quantum matter.

Image by Fabiola Monserrat Pérez Rubio.

M. Frómeta Fernández, D. Hernández-Rajkov, et al., 
Angular momentum of rotating fermionic superfluids by Sagnac phonon interferometry
Nat. Phys., 2026