• Accepted Paper

Nonstabilizerness as a diagnostic of criticality and exceptional points in non-Hermitian spin chains

Cătălin Paşcu Moca, Doru Sticlet, and Balázs Dóra

Phys. Rev. B - Accepted 23 September, 2026

DOI: https://doi.org/10.1103/6vv5-tsql

Abstract

We investigate nonstabilizerness, also known as "magic," to understand criticality and exceptional points in non-Hermitian quantum many-body systems. Our focus is on parity-time (𝒫𝒯) symmetric spin chains, specifically the non-Hermitian transverse-field Ising and XX models. We calculate stabilizer Rényi entropies in their ground states using non-Hermitian matrix product state methods. Our findings show that magic exhibits unique and model-specific signs of phase transitions. In the Ising chain, it peaks near the regular Hermitian-like critical line but disappears across exceptional points. In contrast, in the XX chain, it reaches its maximum at the exceptional line where 𝒫𝒯 symmetry is broken. Finite-size scaling reveals that these effects become more pronounced with larger systems, highlighting nonstabilizerness as a sensitive marker for both quantum criticality and non-Hermitian spectral degeneracies. We also investigate magic in momentum space for the XX model analytically and find that is reaches a minimum around exceptional points. Our results indicate that magic takes extremal values at the exceptional points and serves as a valuable tool for examining complexity, criticality, and symmetry breaking in non-Hermitian quantum matter.

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