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Subsystem Non-Invertible Symmetry Operators and Defects
by Weiguang Cao, Linhao Li, Masahito Yamazaki, Yunqin Zheng
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We explore non-invertible symmetries in two-dimensional lattice models with subsystem $\mathbb Z_2$ symmetry. We introduce a subsystem $\mathbb Z_2$-gauging procedure, called the subsystem Kramers-Wannier transformation, which generalizes the ordinary Kramers-Wannier transformation. The corresponding duality operators and defects are constructed by gaugings on the whole or half of the Hilbert space. By gauging twice, we derive fusion rules of duality operators and defects, which enriches ordinary Ising fusion rules with subsystem features. Subsystem Kramers-Wannier duality defects are mobile in both spatial directions, unlike the defects of invertible subsystem symmetries. We finally comment on the anomaly of the subsystem Kramers-Wannier duality symmetry, and discuss its subtleties.
Submission & Refereeing History
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Reports on this Submission
- Cite as: Anonymous, Report on arXiv:2304.09886v2, delivered 2023-06-23, doi: 10.21468/SciPost.Report.7395
The paper discusses and constructs non-invertible subsystem symmetries in 2+1 dimensions. This is the first example of such a generalized symmetry. It is well-written and contains concrete examples. I recommend the draft for publication.
In both section 2 and 3, the authors discuss KW duality operator/defect 'N' and find its fusion rule in generality. However, they should emphasize that what they actually discuss is the KW interface 'N' between a theory before and after gauging. This interface has to be fused with an isomorphism 'U' which identifies the theory before and after gauging. The KW defect/operator that lives in a single theory is 'NU' rather than just 'N'.
For instance, the authors find the fusion rule
N x N^\dagger
which makes sense when 'N' is an interface. But they do not consider the fusion
NU x NU
which can be different from example to example. Authors should add a short discussion emphasizing where they discuss the interface and when discuss a defect/operator that exists in a single theory.
- Cite as: Anonymous, Report on arXiv:2304.09886v2, delivered 2023-06-14, doi: 10.21468/SciPost.Report.7341
This paper makes a new generalization of the notion of symmetry.
Relationships between different concepts are unclear.
This paper presents a generalization of global symmetries, namely subsystem non-invertible symmetry. Especially, this paper studies the subsystem Kramers-Wannier duality in (2+1)-dimensional spin system and provides the detailed properties of duality operators (defects).
This paper points out a new important concept related to global symmetries. It provides excellent explanations and concrete examples. Therefore, I highly recommend publication of this paper in SciPost.
There are minor points that I would encourage the authors to address.
1 - There seems to be no definition of (H_i^t)^\dagger in the sentence above (2.21). Should it be replaced with (N_i^t)^\dagger?
2 - Even if the subsystem KW duality is a symmetry, subsystem KW duality operators (defects) are not recognized as subsystem symmetry operators (defects), opposed to their names. It is because the names of subsystem KW duality defects come from subsystem symmetry gauging, not from subsystem symmetry itself. If this understanding is correct, then I think that this point should be emphasized to avoid confusion.
3 - There are possibly grammatical errors or typos (pages and lines are according to the arXiv version.).
page 2, line 5: "more than one properties" -> "more than one property"
page 25, line 1: "partition function in" -> "partition function is"
page 29 and 30: The sentence "The number of holonomy variables grows with system size" is repeated. The first one seems unnecessary.