Weak ergodicity breaking from quantum many-body scars



The thermodynamic description of many-particle systems rests on the assumption of ergodicity, the ability of a system to explore all allowed configurations in the phase space. Recent studies on many-body localization have revealed the existence of systems that strongly violate ergodicity in the presence of quenched disorder. Here, we demonstrate that ergodicity can be weakly broken by a different mechanism, arising from the presence of special eigenstates in the many-body spectrum that are reminiscent of quantum scars in chaotic non-interacting systems. In the single-particle case, quantum scars correspond to wavefunctions that concentrate in the vicinity of unstable periodic classical trajectories. We show that many-body scars appear in the Fibonacci chain, a model with a constrained local Hilbert space that has recently been experimentally realized in a Rydberg-atom quantum simulator. The quantum scarred eigenstates are embedded throughout the otherwise thermalizing many-body spectrum but lead to direct experimental signatures, as we show for periodic recurrences that reproduce those observed in the experiment. Our results suggest that scarred many-body bands give rise to a new universality class of quantum dynamics, opening up opportunities for the creation of novel states with long-lived coherence in systems that are now experimentally realizable.

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We acknowledge insightful discussions with M. Lukin and W.W. Ho. C.J.T., A.M. and Z.P. acknowledge support from EPSRC grants EP/P009409/1 and EP/M50807X/1, and Royal Society Research Grant RG160635. D.A. acknowledges support from the Swiss National Science Foundation. This work was initiated during ‘Conference on Many-Body-Localization: Advances in the Theory and Experimental Progress’ at ICTP Trieste.

Author information


  1. School of Physics and Astronomy, University of Leeds, Leeds, UK

    • C. J. Turner
    • , A. A. Michailidis
    •  & Z. Papić
  2. IST Austria, Klosterneuburg, Austria

    • A. A. Michailidis
    •  & M. Serbyn
  3. Department of Theoretical Physics, University of Geneva, Geneva, Switzerland

    • D. A. Abanin


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All authors contributed to developing the ideas, analysing the results and writing the manuscript. C.J.T., A.A.M. and M.S. performed the numerical simulations.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Z. Papić.

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