Curator's Take
This article shows that higher‑order exceptional points (EPs) do more than produce exotic spectral signatures—they directly dictate how genuine multipartite entanglement scales under tiny perturbations in interacting qubit arrays. By exploiting permutation symmetry the authors prove that an N‑qubit system can host EPs of order up to N+1, and they demonstrate that two‑body couplings already generate third‑ and fourth‑order EPs while truly many‑body entangled coalescences require additional three‑body interactions. The result opens a pathway for engineering non‑Hermitian hardware elements that amplify or protect multi‑qubit correlations, a capability that could be leveraged in error‑resilient quantum processors, though experimental realization of the required higher‑order interaction channels remains an open challenge.
— Mark Eatherly
Summary
Exceptional points (EPs) are non-Hermitian spectral singularities exhibiting fractional-power responses, yet their implications for multipartite entanglement of interacting quantum many-body systems remain largely unexplored. Here we develop a general framework that links higher-order non-Hermitian degeneracies to the scaling behavior of genuine multipartite entanglement in interacting identical-qubit systems. Permutation symmetry of the identical qubits decomposes the exponentially large Hilbert space into independent irreducible-representation sectors, thereby constraining the maximal EP order of $N$ qubits to $N+1$ rather than $2^N$. Near an $n$th-order EP, genuine multipartite entanglement inherits the spectral response and generically exhibits a fractional-power scaling under weak perturbations. Explicit examples show that conventional two-body interactions support third- and fourth-order EPs with the corresponding entanglement responses, whereas higher-order EPs with genuine multipartite-entangled coalesced states require additional independent interaction channels, such as three-body interactions. Our results establish a fundamental connection among non-Hermitian degeneracies, multipartite entanglement, and symmetry, extending higher-order EP physics from spectral singularities to genuine many-body quantum correlations.