Genuine quantum scars in many-body spin systems

• Published in: Nature communications Vol. 16; no. 1; pp. 6722 - 7
• Main Authors: Pizzi, Andrea, Kwan, Long-Hei, Evrard, Bertrand, Dag, Ceren B., Knolle, Johannes
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 21.07.2025; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/119; 639/766/483/1139; 639/766/530; Condensed matter physics; Eigenvectors; Electrons; Equilibrium; Hilbert space; Humanities and Social Sciences; multidisciplinary; Orbits; Quantum mechanics; Scars; Science; Science (multidisciplinary); Simulators; Thermalization (energy absorption); Wave functions
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-025-61765-3

Chaos makes isolated systems of many interacting particles quickly thermalize and forget about their past. Here, we show that quantum mechanics hinders chaos in many-body systems: although the quantum eigenstates are thermal and strongly entangled, exponentially many of them are scarred, that is, have an enlarged weight along underlying classical unstable periodic orbits. Scarring makes the system more likely to be found on an orbit it was initialized on, retaining a memory of its past and thus weakly breaking ergodicity, even at long times and despite the system being fully thermal and the eigenstate thermalization hypothesis fulfilled. We demonstrate the ubiquity of quantum scarring in many-body systems by considering a large family of spin models, including some of the most popular ones from condensed matter physics. Our findings, at hand for modern quantum simulators, prove structure in spite of chaos in many-body quantum systems. Chaos causes interacting particles to rapidly thermalize and lose memory of their past. Here, the authors show that, despite thermalization, genuine quantum scarring can imprint structure and long-lived memory effects in the many-body wavefunction.