Quantum many-body scars and Hilbert space fragmentation: A review of exact results

Sanjay Moudgalya, B. Andrei Bernevig, Nicolas Regnault

Research output: Contribution to journalReview articlepeer-review

141 Scopus citations


The discovery of quantum many-body scars (QMBS) both in Rydberg atom simulators and in the Affleck-Kennedy-Lieb-Tasaki spin-1 chain model, have shown that a weak violation of ergodicity can still lead to rich experimental and theoretical physics. In this review, we provide a pedagogical introduction to and an overview of the exact results on weak ergodicity breaking via QMBS in isolated quantum systems with the help of simple examples such as the fermionic Hubbard model. We also discuss various mechanisms and unifying formalisms that have been proposed to encompass the plethora of systems exhibiting QMBS. We cover examples of equally-spaced towers that lead to exact revivals for particular initial states, as well as isolated examples of QMBS. Finally, we review Hilbert space fragmentation, a related phenomenon where systems exhibit a richer variety of ergodic and non-ergodic behaviors, and discuss its connections to QMBS.

Original languageEnglish (US)
Article number086501
JournalReports on Progress in Physics
Issue number8
StatePublished - Aug 2022

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy


  • ETH
  • fragmentations
  • scars


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