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Information Dynamics in a Model with Hilbert Space Fragmentation

by Dominik Hahn, Paul A. McClarty, David J. Luitz

This Submission thread is now published as

Submission summary

Authors (as registered SciPost users): Dominik Hahn · David J. Luitz · Paul A. McClarty
Submission information
Preprint Link:  (pdf)
Date accepted: 2021-09-15
Date submitted: 2021-08-30 15:46
Submitted by: Hahn, Dominik
Submitted to: SciPost Physics
Ontological classification
Academic field: Physics
  • Condensed Matter Physics - Theory
  • Quantum Physics
Approaches: Theoretical, Computational


The fully frustrated ladder - a quasi-1D geometrically frustrated spin one half Heisenberg model - is non-integrable with local conserved quantities on rungs of the ladder, inducing the fragmentation of the Hilbert space into sectors composed of singlets and triplets on rungs. We explore the far-from-equilibrium dynamics of this model through the entanglement entropy and out-of-time-ordered correlators (OTOC). The post-quench dynamics of the entanglement entropy is highly anomalous as it shows clear non-damped revivals that emerge from short connected chunks of triplets and whose persistence is therefore a consequence of fragmentation. We find that the maximum value of the entropy follows from a picture where coherences between different fragments co-exist with perfect thermalization within each fragment. This means that the eigenstate thermalization hypothesis holds within all sufficiently large Hilbert space fragments. The OTOC shows short distance oscillations arising from short coupled fragments, which become decoherent at longer distances, and a sub-ballistic spreading and long distance exponential decay stemming from an emergent length scale tied to fragmentation.

Author comments upon resubmission

We have replied to both reports directly

List of changes

- re-written the entire introduction
- added a second OTOC computation in the appendix
- added a new paragraph discussing the effects of lifted degeneracies
- fixed minor typos
- minor improvements on the plots

Published as SciPost Phys. 11, 074 (2021)

Reports on this Submission

Anonymous Report 2 on 2021-9-2 (Invited Report)


The authors have addressed some of my comments and the quality of the manuscript has significantly improved. However, they did not provide enough evidence to qualify the paper as a "breakthrough" in the field. Therefore, I still do not think that the paper meets the criteria of novelty required by SciPost Physics, but can I now recommend its publication in SciPost Physics Core.

  • validity: -
  • significance: -
  • originality: -
  • clarity: -
  • formatting: -
  • grammar: -

Anonymous Report 1 on 2021-8-30 (Invited Report)


The authors have successfully addressed all of my questions and comments. I recommend publication in SciPost Physics.

  • validity: high
  • significance: good
  • originality: good
  • clarity: top
  • formatting: excellent
  • grammar: excellent

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