Physicists outline a quantum state called a fractional Fermi sea
Calculations suggest ultracold atoms can retain an underlying order at high energies. A companion experimental study is undergoing peer review.
Researchers have developed a theoretical framework for a quantum state they call a fractional Fermi sea, in which atoms retain organized patterns after being driven to high energies. Their study, published in Physical Review Letters, describes how repeatedly switching atomic interactions between attraction and repulsion could produce the state.
The work involves Hanns-Christoph Nägerl’s research group and theoretical physicist Alvise Bastianello of the CNRS and Université Paris-Dauphine. Their calculations examined ultracold cesium atoms restricted to movement in one direction. Beginning with the system’s lowest-energy configuration, the researchers found that interaction cycles could rearrange the atoms into a highly excited but structured state.
The team identified pronounced wave-like patterns known as Friedel oscillations, along with unusual changes in particle correlations over distance. According to the researchers, these features differ from predictions of Tomonaga-Luttinger liquid theory, an established description of interacting particles in one-dimensional systems. The atoms also appear to follow a modified rule for occupying quantum states.
The published work provides the theoretical basis for experiments by Nägerl’s team. A separate paper describing an experimental realization using quantum simulation remains under peer review.
