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Topologically stable ergodicity breaking from emergent higher-form symmetries in generalized quantum loop models
by Charles Stahl, Rahul Nandkishore, Oliver Hart
Submission summary
| Authors (as registered SciPost users): | Oliver Hart · Rahul Nandkishore · Charles Stahl |
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| Preprint Link: | https://arxiv.org/abs/2304.04792v2 (pdf) |
| Date submitted: | 2023-04-25 20:50 |
| Submitted by: | Stahl, Charles |
| Submitted to: | SciPost Physics |
| Ontological classification | |
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| Academic field: | Physics |
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| Approach: | Theoretical |
Abstract
We present a set of generalized quantum loop models which provably exhibit topologically stable ergodicity breaking. These results hold for both periodic and open boundary conditions, and derive from a one-form symmetry (notably not being restricted to sectors of extremal one-form charge). We identify simple models in which this one-form symmetry can be emergent, giving rise to the aforementioned ergodicity breaking as an exponentially long-lived prethermal phenomenon. We unveil a web of dualities that connects these models, in certain limits, to models that have previously been discussed in the literature. We also identify nonlocal conserved quantities in such models that correspond to a pattern of system-spanning domain walls, and which are robust to the addition of arbitrary $k$-local perturbations.
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Reports on this Submission
Strengths
1- Novel results on a timely topic
2- Very clearly written manuscript
Report
The authors introduce a generalized quantum loop models for which they show topologically stable ergodicity breaking. The present work is a generalization of a recent paper by Stephen et., in which a robust ergodicity breaking is demonstrated. The ergodicity breaking in the new class of models is shown to be more robust in that it does not require dense packing nor periodic boundary conditions.
The results represent a novel mechanism allowing for a robust ergodicity breaking and are thus of strong interest. Moreover, the manuscript is well written and all results are presented clearly.
Minor comment: When reading the manuscript, I thought it might be useful to discuss whether the system is strongly or easily fragmented also in the main text.
In summary, this work contains novel results on a timely topic and the manuscript is very clearly written. I thus recommend publication in SciPost.
Strengths
1- Clear presentation
2- Useful formatting and figures
3-Connects interesting and active topics (higher-form symmetries, ergodicity breaking)
Weaknesses
1- The novel parts of this work are mainly based on one specific model and it would be interesting to have a more generic/model-independent answer concerning the connection between ergodicity breaking and higher-form symmetries.
Report
This work presents models that exhibit topologically stable ergodicity breaking. This is accomplished by the generalization of [35], where one-form symmetry was already employed but the ergodicity breaking was "all or nothing", and the generalization of the pair-flip models [41,42] which are generalized to be topologically stable.
The introduction highlights the general question, its challenges, the state-of-the-art, and places the current work into context.
Section 2 is a useful warm-up that reviews the one-dimensional pair-flip model. The authors argue that the fragmentation crucially depends on the restriction to nearest-neighbor-dynamics (a feature that they want to remedy).
Section 3 generalizes the pair-flip model to two dimensions. Using a 1-form symmetry the fragmentation is robust under generic local perturbations (topologically robust) and not "all or nothing" anymore. This section provides the main results of this work.
Section 4 provides further, not strictly necessary, details concerning the two-dimensional model: Other theories which arise as limits or via dualities and a discussion of a generalization to three dimensions (where 2-form symmetries are relevant).
The authors provide a conclusion and two appendices with further details.
This work opens the pathway for the exploration of ergodicity-breaking quantum dynamics that derive from higher-form symmetries and also provides a synergetic link between these different research areas. I am therefore happy to recommend this work for publication in SciPost Physics.
Report
In this manuscript, the authors propose the quad-flip model which can be regarded as generalization of pair flip model in 2D dimension. By adding the constraint of free source, the system shows fragmentation of symmetry sectors, like the pair-flip model. Similarly, in the quad-flip model different Krylov sector can be labeled by the order of non-contractible paths. However, different from the pair-flip model, the fragmentation of Hilbert space is robust unless dynamics evolves degree with the order of system size. The authors also discuss the connection with other models such PXP model and the generalization to 3D case. I think this manuscript is technically correct and has high quality. I agree with publishing this manuscript.