{"id":539208,"date":"2026-07-08T12:37:08","date_gmt":"2026-07-08T12:37:08","guid":{"rendered":"https:\/\/www.newsbeep.com\/ie\/539208\/"},"modified":"2026-07-08T12:37:08","modified_gmt":"2026-07-08T12:37:08","slug":"fractional-fermi-sea-physicists-discover-a-new-phase-of-matter-beyond-established-theory","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/ie\/539208\/","title":{"rendered":"Fractional Fermi Sea: Physicists Discover a New Phase of Matter Beyond Established Theory"},"content":{"rendered":"

\"Ultracold<\/a>Ultracold cesium atoms locked into a hidden, ordered state after being cycled between repulsive and attractive interactions. Credit: University of Innsbruck<\/p>\n

Scientists have engineered a never-before-seen quantum state, uncovering a new phase of matter with hidden order beyond conventional theory.<\/p>\n

Researchers have shown that an unusual quantum state known as a \u201cfractional Fermi sea\u201d can be deliberately created, opening the door to a previously unknown phase of matter. The work, published in Physical Review Letters, was carried out by the N\u00e4gerl group together with theoretical collaborator Alvise Bastianello of the CNRS and Universit\u00e9 Paris-Dauphine. The study provides the theoretical foundation for recent experimental work led by Hans-Christoph N\u00e4gerl\u2019s group in the Department of Experimental Physics.<\/p>\n

Creating a New Quantum State<\/p>\n

The team focused on ultracold Cesium atoms confined to a single dimension. By repeatedly changing how strongly the atoms interacted, cycling them between strong repulsion and strong attraction, they pushed the system far from its normal equilibrium state. Rather than behaving according to the well-established Tomonaga-Luttinger liquid theory, the atoms entered an entirely new critical phase of matter.<\/p>\n

This newly predicted phase arises through a process called quantum engineering, showing that carefully controlled interaction cycles can produce forms of quantum matter that do not occur naturally under ordinary conditions.<\/p>\n

What Is a Fractional Fermi Sea?<\/p>\n

At extremely low temperatures, quantum particles normally arrange themselves according to well-defined rules. As Alvise Bastianello explains: \u201cFermions, for instance, stack neatly into the available energy states to form the so-called \u2018Fermi sea\u2019. 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?\u201d<\/p>\n

The researchers found that this carefully designed interaction cycle drives atoms from their ground state into a highly excited yet surprisingly organized non-equilibrium state. They call this unusual arrangement a \u201cfractional\u201d Fermi sea because the particles appear to obey a reduced occupancy rule.<\/p>\n

\u201cInstead of simply heating the system, the interaction cycle reorganizes the atoms into a new many-body state,\u201d says Yi Zeng, the study\u2019s lead author. \u201cThis gives us a controlled way to explore quantum matter beyond the usual equilibrium paradigms.\u201d<\/p>\n

Hidden Order Beyond Established Theory<\/p>\n

The fractional Fermi sea displays several distinctive features. Mathematical relationships between the particles produce pronounced ripples known as Friedel oscillations, along with characteristic decay patterns across all levels of repulsive interaction.<\/p>\n

These signatures clearly separate the new state from Tomonaga-Luttinger liquids, which have long served as the standard framework for describing one-dimensional quantum systems.<\/p>\n

\u201cThis state is highly excited, but it is not random,\u201d says Hanns-Christoph N\u00e4gerl, the group\u2019s leader. \u201cIt has a hidden order that becomes visible in its correlations.\u201d He adds: \u201cWe are not yet sure how we should name these new quasiparticles. Perhaps \u2018super-Fermions\u2019?\u201d<\/p>\n

A New Frontier for Quantum Simulation<\/p>\n

The unique behavior of fractional Fermi seas points to an entirely new exotic critical phase of matter and provides researchers with a new way to investigate universal quantum behavior using cold atom simulators.<\/p>\n

As N\u00e4gerl explains: \u201cThe 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.\u201d<\/p>\n

A companion paper describing the experimental realization of fractional Fermi seas through quantum simulation is currently under review.<\/p>\n

References:<\/p>\n

\u201cExotic Critical States as Fractional Fermi Seas in the One-Dimensional Bose Gas\u201d by Alvise Bastianello, Yi Zeng, Sudipta Dhar, Zekui Wang, Xudong Yu, Milena Horvath, Grigori E. Astrakharchik, Yanliang Guo, Hanns-Christoph N\u00e4gerl and Manuele Landini, 9 June 2026, Physical Review Letters.
DOI: 10.1103\/j3s5-gjpf<\/a><\/p>\n

\u201cRealization of fractional Fermi seas\u201d by Yi Zeng, Alvise Bastianello, Sudipta Dhar, Zekui Wang, Xudong Yu, Milena Horvath, Grigori E. Astrakharchik, Yanliang Guo, Hanns-Christoph N\u00e4gerl and Manuele Landini, 19 May 2026, arXiv.
DOI: 10.48550\/arXiv.2602.17657<\/a><\/p>\n

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