Abstract
We summarize different approaches to the theory of quantum graphs and provide several ways to construct concrete examples. First, we classify all undirected quantum graphs on the quantum space \(M_2\). Secondly, we apply the theory of 2-cocycle deformations to Cayley graphs of abelian groups. This defines a twisting procedure that produces a quantum graph, which is quantum isomorphic to the original one. For instance, we define the anticommutative hypercube graphs. Thirdly, we construct an example of a quantum graph, which is not quantum isomorphic to any classical graph.
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Notes
This actually makes it quite easy to classify all such graphs, which we are going to do in Sect. 3.3.
Fans of chemistry might enjoy the following parallel: The finite quantum sets X are molecules, which consist of atoms \(M_{n_i}({\mathbb {C}})\). The atoms \(M_{n_i}\) are defined by their proton number \(n_i\), they have atomic mass \(n_i^2\), and they cannot be decomposed by any chemical processes (taking quantum subsets), but can be split by nuclear fission (taking quantum set quotient).
Such a concrete realization is also known as a nice unitary error basis see [16].
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I would like to thank Simon Schmidt, Christian Voigt, and Moritz Weber for valuable discussions about quantum graphs. I thank to Julien Bichon for discussing monoidal equivalences related to \(SO_n\). This work was supported by the project OPVVV CAAS CZ.02.1.01/0.0/0.0/16_019/0000778.
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Gromada, D. Some examples of quantum graphs. Lett Math Phys 112, 122 (2022). https://doi.org/10.1007/s11005-022-01603-5
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DOI: https://doi.org/10.1007/s11005-022-01603-5