The sound of the infinitely small, the secrets of Fermi gases revealed

In this state, particles tend to pair together to form a condition of superfluidity, that is, a state of matter in which friction disappears completely. To study this phenomenon, the researchers imagined the superfluid as a fluid flowing in a ring, within which sound waves are propagated in opposite directions. Since the fluid is rotating, the waves that move following the motion of the matter are slightly different from those that proceed against the current; a physical principle similar to that which causes the perceived pitch of a moving siren to vary.

By measuring these tiny differences, it was possible to directly observe the internal structure of the system. As researchers Marcia Fròmeta Fernandez and Diego Hernandez-Rajkov explain, this approach made it possible to detect how sound changes based on the direction of propagation with respect to the flow of the superfluid, providing the key to mapping Fermi gases. The precision of the detections demonstrated that the circulation of the superfluid is constrained to quantized values, confirming that superfluidity in such gases arises from the coupling of fermions into composite units known as Cooper pairs.

Fermions are the elementary particles that make up matter, electrons, protons and neutrons. Unlike other particles, they follow the Pauli exclusion principle, which prevents them from occupying the same quantum state at the same time, thus ensuring the stability and solid structure of everything around us.

Professor Francesco Scazza, professor at the University of Trieste, clarified: “Our observation demonstrates that the superfluid is made up of fermions that couple two by two, forming composite quantum units of double mass, the so-called Cooper pairs, similarly to what happens in superconductors“. This methodology, based on atomic interferometry, has proven to be extremely effective for studying the reduction of superfluidity as a function of thermal increase, offering new analytical tools to delve deeper into the mechanisms of superconductivity and dynamics of matter still under academic investigation.

This achievement comes a century after the formulation of Fermi statistics, offering unprecedented perspectives for the development of advanced quantum technologies, as reiterated by physicists Massimo Inguscio and Sandro Stringari: “The work opens a new avenue to study the collective behavior of particles and deepen our understanding of the mechanisms underlying superfluidity and superconductivity.”.