Physicists create a bizarre new quantum state called a fractional fermi sea

Physicists have discovered a strange new state of quantum matter in which ultracold atoms defy familiar organizational rules, forming a highly excited yet surprisingly orderly configuration called a "fractional Fermi sea." The discovery challenges established quantum theories and hints at exotic quasiparticles that scientists have dubbed potential "super-Fermions.". Physicists create a bizarre new quantum state called a fractional fermi sea. Even more surprising, the particles maintain a remarkable hidden order despite being driven into an extremely energetic state.

In a study published in Physical Review Letters, researchers from the group led by Hanns-Christoph Nägerl, working with theoretical physicist Alvise Bastianello of the CNRS and Université Paris-Dauphine, describe how to engineer an exotic quantum state known as a "fractional Fermi sea." The breakthrough involves pushing ultracold cesium atoms far beyond their normal conditions by repeatedly changing how strongly they attract or repel one another. Rather than simply becoming disordered, the particles rearrange themselves into an unusual configuration that behaves differently from the quantum systems scientists have traditionally studied. The theoretical findings provide the foundation for recent experimental research conducted by Nägerl’s team at the Department of Experimental Physics.

Pushing Quantum Particles Beyond Their Normal Limits Under ordinary conditions, quantum particles follow well-established rules that determine how they arrange themselves, particularly at extremely low temperatures. One important example involves fermions, a category of particles that includes electrons. These particles cannot all occupy the same quantum state, so they fill available energy levels according to specific restrictions.