Insider Brief<\/p>\n
Researchers reported that a driven one-dimensional gas of ultracold cesium atoms can be engineered into a highly ordered non-equilibrium quantum state known as a fractional Fermi sea.<\/p>\n
The study shows that cyclically changing interactions between strongly repulsive and strongly attractive regimes can reorganize atoms into a highly excited state rather than simply heating the system.<\/p>\n
The fractional Fermi sea displays correlation patterns that differ from Tomonaga-Luttinger liquids, suggesting a new exotic critical phase for cold-atom quantum simulation.<\/p>\n
Image: Ultracold cesium atoms locked into a hidden, ordered state after being cycled between repulsive and attractive interactions. (University of Innsbruck)<\/p>\n
PRESS RELEASE \u2014 In a new study published in\u00a0Phys\u00adical Review Letters, a team of the N\u00e4gerl group jointly with theory collab\u00ado\u00adrator Alvise Bastianello from the CNRS and the Univer\u00adsit\u00e9 Paris-Dauphine demon\u00adstrates that highly unusual quantum states known as \u201cfrac\u00adtional Fermi seas\u201d can be quantum engi\u00adneered.<\/p>\n
By driving quantum particles, here ultracold Cesium atoms under one-dimensional confinement, far out of equilibrium through cyclic changes of the particle interaction, a novel critical phase of matter is found to emerge, going beyond what is known from the celebrated Tomonaga-Luttinger liquid theory. The new publication serves as the theoretical companion and the foundation for recent experimental work in the group of Hans-Christoph N\u00e4gerl at the\u00a0Department of Experimental Physics<\/a>.<\/p>\n Usually, particles in the quantum world follow strict rules about how they organize themselves at low temperatures. 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 The researchers show that a specific interaction cycle forces the initial ground-state atoms into a highly excited, yet highly ordered, non-equilibrium configuration. This has been named a \u201cfractional\u201d Fermi sea, where the particles seemingly follow 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 leading author of this study. \u201cThis gives us a controlled way to explore quantum matter beyond the usual equilibrium paradigms.\u201d\u00a0<\/p>\n The consequences of this fractional state are striking. The mathematical correlations between the particles show prominent ripples\u2014known as Friedel oscillations\u2014and distinct decay patterns at any level of repulsive interaction. Crucially, this new state shows features that distinct from the Tomonaga-Luttinger liquids, which has long been the established model for understanding one-dimensional quantum systems. \u201cThis state is highly excited, but it is not random,\u201d says Hanns-Christoph N\u00e4gerl, the group 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 The appearance of these specific signatures points to an entirely new, exotic critical phase, opening up fresh pathways for exploring universal behavior in cold-atom quantum simulators. As Hanns-Christoph N\u00e4gerl says: \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 The sister publication on the experimental realization of fractional Fermi seas in the spirit of quantum simulation is yet in the reviewing process.<\/p>\n Publications:
\u00a0Exotic critical states as fractional Fermi seas in the one-dimensional Bose gas. A. Bastianello, Y. Zeng, S. Dhar, Z. Wang, X. Yu, M. Horvath, G. E. Astrakharchik, Y. Guo, H.-C. N\u00e4gerl, M. Landini\u00a0Physical Review Letters\u00a0136, 230402 (2026) DOI:\u00a010.1103\/j3s5-gjpf<\/a>, preprint at\u00a0arxiv.org\/abs\/2602.17656<\/a>
\u00a0Realization of fractional Fermi seas. Yi Zeng, Alvise Bastianello, Sudipta Dhar, Zekui Wang, Xudong Yu, Milena Horvath, Grigori E. Astrakharchik, Yanliang Guo, Hanns-Christoph N\u00e4gerl, Manuele Landini.\u00a0preprint at\u00a0arxiv.org\/abs\/2602.17657<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"Insider Brief Researchers reported that a driven one-dimensional gas of ultracold cesium atoms can be engineered into a…\n","protected":false},"author":2,"featured_media":732541,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[49],"tags":[199,79],"class_list":["post-732540","post","type-post","status-publish","format-standard","has-post-thumbnail","category-physics","tag-physics","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/732540","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/comments?post=732540"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/732540\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media\/732541"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media?parent=732540"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/categories?post=732540"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/tags?post=732540"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}