Existence at the smallest, coldest scales is ruled by quantum statistics, which determine the behavior of bosons<\/a> and fermions<\/a>: the two families of fundamental particles thought to comprise every thing in the Universe.<\/p>\n Bosons are force-carrying particles, like photons or the famous Higgs boson<\/a>. These can occupy the same quantum state, meaning that limitless bosons<\/a> can ‘overlap’ on top of each other and act like coherent waves.<\/p>\n Fermions are particles like electrons and the quarks that make up protons and neutrons. They cannot ‘overlap’<\/a> because only a single fermion<\/a> may occupy a quantum state, as per the famous Pauli exclusion principle<\/a> \u2013 which also explains why stellar zombies, like neutron stars<\/a> and white dwarfs<\/a>, don’t collapse into infinitely small black holes<\/a>.<\/p>\n Recently, physicists have plied these principles to experimentally<\/a> and theoretically<\/a> describe a strange new phase of quantum matter likened to a sea of self-organized particles.<\/p>\n “Fermions, for instance, stack neatly into the available energy states to form the so-called ‘Fermi sea’,” says<\/a> Alvise Bastianello, a theoretical physicist at the French National Centre for Scientific Research (CNRS) and the Univer\u00adsit\u00e9 Paris-Dauphine.<\/p>\n “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?”<\/p>\n To find out, the researchers first created an exotic state of matter<\/a> called a Bose gas. This comprised a collection of approximately 70,000 cesium atoms cooled to an otherworldly temperature of just a few nanoKelvin, equivalent to billionths of a degree above absolute zero.<\/p>\n In such extreme conditions, atoms lose their individuality and begin acting as a nebulously unified entity.<\/p>\n The researchers then confined this singular substance within one-dimensional tubes, generated by a two-dimensional optical lattice, a webwork of lasers that traps atoms so they can be observed<\/a>.<\/p>\n Finally, researchers subjected this matter to repeated interaction cycles, in which they induced its constituent atoms to strongly repulse then attract each other.<\/p>\n In doing so, they birthed an entirely new, unexpectedly exotic phase of quantum matter, a fractional Fermi sea.<\/p>\n As mentioned, bosons can occupy quantum states without restriction, but fermions cannot. Therefore, the ‘fractionality’ of this sea represents a sort-of in-between, in which quantum states can be only partially occupied \u2013 a mechanism that may only manifest in lower-dimensional experiments.<\/p>\n Subscribe to ScienceAlert’s free fact-checked newsletter<\/p>\n The cyclical attraction and repulsion pulses also yield a counter-intuitive result. Rather than firing up or randomly dispersing the particles, they do the opposite.<\/p>\n “Instead of simply heating the system, the interaction cycle reorganizes the atoms into a new many-body state,” says<\/a> Yi Zeng, condensed matter physicist at the University of Innsbruck in Austria and the study’s lead author.<\/p>\n Research leader Hanns-Christoph N\u00e4gerl, a professor at the University of Innsbruck who specializes in experimental quantum physics, explains<\/a>:<\/p>\n “This state is highly excited, but it is not random. It has a hidden order that becomes visible in its correlations.”<\/p>\n Given its oddly complex interactions, including apparent ripples called Friedel oscillations \u2013 the “smoking gun”<\/a> evidence of a fractional Fermi sea \u2013 the researchers are unsure of how to label their labile matter.<\/p>\n “We are not yet sure how we should name these new quasiparticles<\/a>. Perhaps ‘super-Fermions’?” suggests N\u00e4gerl.<\/p>\n This novel experiment offers a unique pathway for exploring the interactions of cold-atom quantum systems, to probe how our macro-reality emerges from the weirdness occurring at the most foundational scales.<\/p>\n “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,” N\u00e4gerl says<\/a>.<\/p>\n Related: Scientists Discover a New Quantum State of Matter Once Considered Impossible<\/a><\/strong><\/p>\n As a result, this work may help improve quantum information and sensing capabilities, allowing high-precision data processing and measurements to link the world<\/a> \u2013 with untold potential for improving material science, biomedicine, and encryption<\/a> technologies, among many others.<\/p>\n This research was published in Physical Review Letters<\/a> and is available at the pre-print server arXiv<\/a>.<\/p>\n This article was fact-checked by Jess Cockerill<\/a> and edited by Michael Irving<\/a>. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know<\/a>.<\/p>\n![\"Experimental](\"https:\/\/www.europesays.com\/ie\/wp-content\/uploads\/2026\/07\/9f7c299848be2f147697b8e39b771f58.jpeg\"\/)
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Computer model of a similar state of matter, a Bose-Einstein condensate<\/a>, illustrating the wave-like action of atoms that have been chilled to just fractions of a degree above absolute zero. (NASA\/NIST)<\/a><\/p>\n![\"Subscribe](\"https:\/\/www.europesays.com\/ie\/wp-content\/uploads\/2026\/07\/1783082953_594_ef67e8189dd8a81822ba8e99a83ad014.jpeg\"\/)
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Illustration of ultra-cold cesium atoms being coerced into a hidden, ordered state after being subjected to interaction cycles comprising rounds of repulsion and attraction. (University of Innsbruck<\/a>)<\/p>\n