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Highly Entangled 2D Ground States: Tensor Networks and Correlation Functions

by Olai B. Mykland, Zhao Zhang

Submission summary

Authors (as registered SciPost users): Zhao Zhang
Submission information
Preprint Link: scipost_202503_00047v1  (pdf)
Date submitted: March 25, 2025, 12:16 p.m.
Submitted by: Zhao Zhang
Submitted to: SciPost Physics
Ontological classification
Academic field: Physics
Specialties:
  • Condensed Matter Physics - Theory
  • Mathematical Physics
  • Quantum Physics
Approach: Theoretical

Abstract

In this article we present analytical results on the exact tensor network representations and correlation functions of the first examples of 2D ground states with quantum phase transitions between area law and extensive entanglement entropy. The tensor networks constructed are one dimension higher than the lattices of the physical systems, allowing entangled physical degrees of freedoms to be paired with one another arbitrarily far away. Contraction rules of the internal legs are specified by a simple translationally invariant set of rules in terms of the tessellation of cubes or prisms in 3D space. The networks directly generalize the previous holographic tensor networks for 1D Fredkin and Motzkin chains. We also analyze the correlation in the spin and color sectors from the scaling of the height function of random surfaces, revealing additional characterizations of the exotic phase transitions.

Author indications on fulfilling journal expectations

  • Provide a novel and synergetic link between different research areas.
  • Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
  • Detail a groundbreaking theoretical/experimental/computational discovery
  • Present a breakthrough on a previously-identified and long-standing research stumbling block
Current status:
In refereeing

Reports on this Submission

Report #2 by Anonymous (Referee 2) on 2025-9-15 (Invited Report)

Strengths

The manuscript addresses the problem of constructing exact tensor network representations for highly entangled ground states in two dimensions, extending the holographic tensor networks known for 1D Fredkin and Motzkin chains. These models are among the rare examples that exhibit transitions between area-law and extensively scaling entanglement entropy. Given the general lack of analytically tractable examples of such exotic entanglement structures in higher dimensions, the present work makes a valuable contribution by formulating explicit tensor networks based on cubic and prismatic tilings. The technical development is sound, and the presentation is detailed. The results will be of interest to researchers working on tensor networks, entanglement scaling, and related aspects of quantum many-body physics.

Report

The paper is already well written and technically sound. I only have two minor comments concerning the references:

On page 2, the authors mention the entanglement entropy of "free fermionic systems with a Fermi sea in any dimension," citing Ref. [9]. I suggest replacing "Fermi sea" with "Fermi surface": the term "Fermi sea" could also refer to a gapped situation (e.g., a fully occupied band separated by an empty band with a gap) or systems with only Dirac points, where the area law is restored without a logarithmic violation. In addition, the parallel work by M. Wolf, Phys. Rev. Lett. 96, 010404 (2006), published back-to-back with Ref. [9], should also be cited. Both papers independently established the logarithmic violation of the area law for free fermions with a Fermi surface.

Regarding the higher-dimensional generalization related to Ref. [10], the authors currently cite Ref. [11] only. However, an earlier contribution by G. Sierra and collaborators, J. Stat. Mech. (2015) P06002, should also be cited for completeness.

Other than these points, I have no major criticisms. The technical constructions in the main sections appear correct and carefully explained.

In conclusion, I recommend publication in SciPost Physics once the above citation issues are addressed.

Recommendation

Publish (easily meets expectations and criteria for this Journal; among top 50%)

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

Report #1 by Anonymous (Referee 1) on 2025-8-3 (Invited Report)

Strengths

1- Non trivial results 2- novel construction of a 3d exact tensor network describing the ground state of a 2D quantum model 3- The paper supplies clear motivations and background material

Weaknesses

1- Results are of academic interest 2- Require significant effort to fully understand.

Report

In this paper, the authors construct an exact tensor network description of a class of 2D height models that serve as paradigms for exotic phase transitions, particularly in terms of entanglement. These models are frustration-free and allow our understanding of the ground state as a geometrical object. The construction is challenging in that it involves constructing 3D surfaces and the 3D tensor network, and the authors appear to have succeeded in doing so, as far as I could verify. The main results are the descriptions of the 3D tensors, as depicted in Figures 5 and 12. The authors also provide some insight into correlation functions, which are summarized nicely in tables at the end, both for height and color correlations. The appropriate literature is cited in a transparent and helpful manner, and an extensive appendix covers both the original setup (the definition of the models is lengthy by itself) as well as many details of the main text. Clearly, much work has gone into writing this paper and, in particular, polishing the presentation.
The results serve to complete an obvious next step in the field of highly entangled states - that of an explicit tensor network in 3D, and as such are of sufficient quality and interest for publication.
The only thing I would suggest that can improve the paper, but this is optional (I would at least suggest that the authors do that if they give talks on the subject!) is to find a way to illustrate the actual 3D construction in a more intuitive way than just listing the prisms that do the job.

Recommendation

Publish (easily meets expectations and criteria for this Journal; among top 50%)

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

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