Researchers have created a new quantum state known as a fractional Fermi sea using ultracold cesium atoms in one dimension. The work, published in Physical Review Letters, shows particles organizing in ways that exceed standard theories.
The study was conducted by the Nägerl group at the University of Innsbruck, in collaboration with theorist Alvise Bastianello. Scientists repeatedly cycled the atoms between strong repulsion and attraction to drive them into the new state.
Yi Zeng, the lead author, noted that the cycle reorganizes atoms into a highly excited yet ordered configuration. This produces a reduced occupancy rule unlike the usual Fermi sea.
Hanns-Christoph Nägerl said the state displays hidden order visible in particle correlations. He questioned what to call the new quasiparticles, suggesting perhaps super-Fermions.
A companion experimental paper remains under review. The discovery provides a route to explore quantum matter beyond equilibrium models using cold-atom simulators.