Excitations in (3+1)-dimensional [(3+1)D] topologically ordered phases have very rich structures. (3+1)D topological phases support both pointlike and stringlike excitations, and in particular the loop (closed string) excitations may admit knotted and linked structures. In this work, we ask the following question: How do different types of topological excitations contribute to the entanglement entropy or, alternatively, can we use the entanglement entropy to detect the structure of excitations, and further obtain the information of the underlying topological order? We are mainly interested in (3+1)D topological order that can be realized in Dijkgraaf-Witten (DW) gauge theories, which are labeled by a finite group
G and its group 4-cocycle $\ensuremath{\omega}\ensuremath{\in}{\mathcal{H}}^{4}[G;\text{U}(1)]$ up to group automorphisms. We find that each topological excitation contributes a universal constant
lndi to the entanglement entropy, where
di is the quantum dimension that depends on both the structure of the excitation and the data $(G,\phantom{\rule{0.16em}{0ex}}\ensuremath{\omega})$. The entanglement entropy of the excitations of the linked/unlinked topology can capture different information of the DW theory $(G,\phantom{\rule{0.16em}{0ex}}\ensuremath{\omega})$. In particular, the entanglement entropy introduced by Hopf-link loop excitations can distinguish certain group 4-cocycles $\ensuremath{\omega}$ from the others.
We study the structure of topological phases and their boundaries in the projected entangled-pair states (PEPS) formalism. We show how topological order in a system can be identified from the structure of the PEPS transfer operator and subsequently use these findings to analyze the structure of the boundary Hamiltonian, acting on the bond variables, which reflects the entanglement properties of the system. We find that in a topological phase, the boundary Hamiltonian consists of two parts: A universal nonlocal part which encodes the nature of the topological phase and a nonuniversal part which is local and inherits the symmetries of the topological model, which helps to infer the structure of the boundary Hamiltonian and thus possibly of the physical edge modes.
This work proposes a structural and topological framework for the description of multipartite quantum entanglement within the Theory of Structural Articulation (TSA). Entanglement is interpreted not as an abstract algebraic property of quantum states in Hilbert space, but as a manifestation of the connectivity of a single structural defect embedded in an underlying medium. The fundamental carrier of quantum structure is modeled as a hypergraph of difference connectivity, whose irreducible hyperedges encode genuine multipartite correlations. Observable entanglement is described as a projection of this hypergraph onto a connectivity graph of pairwise correlations. A topological invariant—the first Betti number of the connectivity graph—is introduced and shown to characterize redundancy of correlation pathways and robustness of multipartite quantum resources against local losses. This provides a unified topological classification of GHZ-type states, W states, and cluster states, and explains qualitative differences in their stability. Beyond static classification, the work formulates a thermodynamic mechanism for the emergence of structural complexity in open quantum systems. Dissipative relaxation of structural conflict drives spontaneous closure of connectivity loops, leading to growth of topological redundancy and formation of highly connected phases. Multipartite entanglement is thereby interpreted as an equilibrium or quasistationary phase of a dense system of structural defects, rather than as the result of fine-tuned unitary control. The results offer a structural interpretation of multipartite entanglement, linking topology, robustness, and self-organization, and suggest new perspectives on the physical origin of scalable quantum resources for quantum information processing and quantum memory.