A fractional Fermi sea is an exotic, highly excited quantum state in which fermion-like particles fill energy levels according to a modified occupation rule, instead of stacking one per state as they do in an ordinary low-temperature Fermi sea. Physicists at the University of Innsbruck and CNRS/Université Paris-Dauphine described how to create it in a one-dimensional gas of ultracold cesium atoms by repeatedly cycling the atoms’ interactions between strong repulsion and strong attraction.
Rather than simply heating up and becoming disordered, the atoms keep a hidden order that shows up in their correlations, including pronounced Friedel oscillations, and the state does not fit the long-standing Tomonaga-Luttinger liquid theory of one-dimensional quantum systems. The theory, led by Yi Zeng with Alvise Bastianello and Hanns-Christoph Nägerl, was published in Physical Review Letters and underpins recent experiments by Nägerl’s group.
Image: Cesium metal sealed in a glass ampoule, by Dnn87, CC BY-SA 3.0, via Wikimedia Commons.
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