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Symmetry resolved entanglement in gapped integrable systems: a corner transfer matrix approach
by Sara Murciano, Giuseppe Di Giulio, Pasquale Calabrese
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Authors (as registered SciPost users):  Giuseppe Di Giulio · Sara Murciano 
Submission information  

Preprint Link:  https://arxiv.org/abs/1911.09588v2 (pdf) 
Date submitted:  20200109 01:00 
Submitted by:  Murciano, Sara 
Submitted to:  SciPost Physics 
Ontological classification  

Academic field:  Physics 
Specialties: 

Approach:  Theoretical 
Abstract
We study the symmetry resolved entanglement entropies in gapped integrable lattice models. We use the corner transfer matrix to investigate two prototypical gapped systems with a U(1) symmetry: the complex harmonic chain and the XXZ spinchain. While the former is a free bosonic system, the latter is genuinely interacting. We focus on a subsystem being half of an infinitely long chain. In both models, we obtain exact expressions for the charged moments and for the symmetry resolved entropies. While for the spin chain we found exact equipartition of entanglement (i.e. all the symmetry resolved entropies are the same), this is not the case for the harmonic system where equipartition is effectively recovered only in some limits. Exploiting the gaussianity of the harmonic chain, we also develop an exact correlation matrix approach to the symmetry resolved entanglement that allows us to test numerically our analytic results.
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Reports on this Submission
Anonymous Report 2 on 2020220 (Invited Report)
 Cite as: Anonymous, Report on arXiv:1911.09588v2, delivered 20200220, doi: 10.21468/SciPost.Report.1523
Strengths
Pedagogical introduction
Detailed calculations
Timely results
Report
In quantum systems with symmetry, the entanglement entropy of a subsystem can be decomposed into contributions coming from different symmetry charge sectors. This leads naturally to the definition of the symmetryresolved entanglement entropy, which has been the topic of a handful of recent studies.
In this manuscript, the authors compute analytically, using the corner transfer matrix approach, the symmetryresolved entanglement entropy for two specific integrable models: the complex harmonic chain and the XXZ chain. Some analytic results are supported by numerical calculations. Perhaps most interestingly, the second example was found to satisfy an equipartition of symmetryresolved entanglement: the entanglement entropy is distributed exactly evenly among the charge sectors. This need not be true generally, and so therefore raises the important question of what is necessary for the equipartition to be satisfied exactly. These results will be a useful reference point for future studies of symmetryresolved entanglement entropy.
The paper is well written and pedagogical. I support publication of this paper in SciPost as is.
Anonymous Report 1 on 202029 (Invited Report)
 Cite as: Anonymous, Report on arXiv:1911.09588v2, delivered 20200209, doi: 10.21468/SciPost.Report.1485
Strengths
The paper is well written with all the technical derivations beautifully presented. The physical result of equipartition or lack of it in the different symmetry sectors is very interesting.
Weaknesses
Motivation for studying symmetry resolved entanglement is absent.
Report
The paper can be published after the recommended changes are made.
Requested changes
Some more motivation for studying symmetry resolved entanglement is needed. The current manuscript has the following comment in the introduction "it became clear that it is also important to understand the relation between entanglement and symmetries.....", followed by citation
to some papers. I would recommend some more discussion here to strengthen the motivation.