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

Science News from research organizations Physicists create a strange new quantum state called a fractional fermi sea Date: June 29, 2026 Source: University of Innsbruck Summary: Researchers have shown that ultracold atoms can be driven into a strange new quantum state called a fractional Fermi sea, where particles organize themselves in unexpected ways. The discovery points to a new phase of matter that goes beyond established quantum theories and could expand the possibilities of quantum simulation. Share: Facebook Twitter Pinterest LinkedIN Email FULL STORY Ultracold cesium atoms locked into a hidden, ordered state after being cycled between repulsive and attractive interactions. Credit: University of Innsbruck Researchers have shown that an unusual class of quantum states known as "fractional Fermi seas" can be deliberately created, according to a new study published in Physical Review Letters. The work was carried out by the Nägerl group together with theoretical physicist Alvise Bastianello of CNRS and Université Paris-Dauphine. The study demonstrates how a new critical phase of matter can emerge when quantum particles are pushed far from their normal equilibrium conditions. Using ultracold cesium atoms confined to one dimension, the researchers repeatedly altered how strongly the particles interacted with one another. The resulting state goes beyond the behavior predicted by the well-known Tomonaga-Luttinger liquid theory, a cornerstone for understanding one-dimensional quantum systems. This publication provides the theoretical framework for recent experimental research conducted in the group of Hans-Christoph Nägerl at the Department of Experimental Physics. Creating a Fractional Fermi Sea At very low temperatures, quantum particles typically follow strict rules that determine how they arrange themselves.

As Alvise Bastianello explains: "Fermions, for instance, stack neatly into the available energy states to form the so-called 'Fermi sea'. But what happens if one forces interacting atoms to continuously cycle through extreme conditions, smoothly shifting them from strongly repelling each other to strongly attracting each other?" The researchers found that carefully repeating this interaction cycle drives atoms out of their normal ground state and into a highly excited yet remarkably organized configuration. They call this state a "fractional" Fermi sea because the particles appear to obey a reduced occupancy rule. "Instead of simply heating the system, the interaction cycle reorganizes the atoms into a new many-body state," says Yi Zeng, the leading author of this study. "This gives us a controlled way to explore quantum matter beyond the usual equilibrium paradigms." Hidden Order in an Excited Quantum State The newly created state displays several unusual characteristics. Mathematical correlations between particles reveal pronounced ripples, known as Friedel oscillations, along with distinctive decay behavior across all levels of repulsive interactions. Perhaps most importantly, the state exhibits properties that differ from those expected for Tomonaga-Luttinger liquids, which have long served as the standard description of one-dimensional quantum matter. "This state is highly excited, but it is not random," says Hanns-Christoph Nägerl, the group leader. "It has a hidden order that becomes visible in its correlations." He adds: "We are not yet sure how we should name these new quasiparticles. Perhaps 'super-Fermions'?" A New Critical Phase of Matter These distinctive signatures indicate the presence of an entirely new and exotic critical phase. The discovery offers a new route for investigating universal quantum behavior using cold-atom simulators. As Hanns-Christoph Nägerl says: "The discovery of fractional Fermi seas shows how far we can push quantum simulation: not only reproducing known models, but creating and probing states that go beyond established paradigms." A companion paper describing the experimental realization of fractional Fermi seas through quantum simulation is currently under review. RELATED TOPICS Matter & Energy Physics Graphene Nature of Water Inorganic Chemistry Chemistry Quantum Physics Materials Science Optics RELATED TERMS Introduction to quantum mechanics Nanoparticle Quantum computer Particle physics Physics Quantum entanglement Robot Quantum dot Story Source: Materials provided by University of Innsbruck. Note: Content may be edited for style and length. Journal References: Alvise Bastianello, Yi Zeng, Sudipta Dhar, Zekui Wang, Xudong Yu, Milena Horvath, Grigori E. Astrakharchik, Yanliang Guo, Hanns-Christoph Nägerl, Manuele Landini.

Exotic Critical States as Fractional Fermi Seas in the One-Dimensional Bose Gas.

Physical Review Letters, 2026; 136 (23) DOI: 10.1103/j3s5-gjpf Yi Zeng, Alvise Bastianello, Sudipta Dhar, Zekui Wang, Xudong Yu, Milena Horvath, Grigori E. Astrakharchik, Yanliang Guo, Hanns-Christoph Nägerl, Manuele Landini. Realization of fractional Fermi seas. arXiv, 19 May 2026 DOI: 10.48550/arXiv.2602.17657 Cite This Page: MLA APA Chicago University of Innsbruck. "Physicists create a strange new quantum state called a fractional fermi sea." ScienceDaily. ScienceDaily, 29 June 2026. . University of Innsbruck. (2026, June 29). Physicists create a strange new quantum state called a fractional fermi sea. ScienceDaily. Retrieved June 29, 2026 from www.sciencedaily.com/releases/2026/06/260619101330.htm University of Innsbruck. "Physicists create a strange new quantum state called a fractional fermi sea." ScienceDaily. www.sciencedaily.com/releases/2026/06/260619101330.htm (accessed June 29, 2026). Explore More from ScienceDaily RELATED STORIES A Bizarre New State of Matter May Be Hiding Inside Uranus and Neptune Apr. 21, 2026 — Deep inside planets like Uranus and Neptune, scientists may have uncovered a bizarre new state of matter where atoms behave in unexpected ways. Advanced simulations suggest that carbon and hydrogen, ...

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