Analytic method for GGE quasi-momentum distribution in degenerate free-fermion models plus a conjecture adjusting the quasi-particle entanglement formula, tested numerically with good agreement on local observables but small deviations on entanglement.
Free fermions in disguise without exponential degeneracies
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abstract
Recently, a number of spin chain models have been discovered that are solvable via hidden free-fermionic structures, going beyond the Jordan-Wigner paradigm. However, all examples in the literature displayed degeneracies that grow exponentially with the volume and that are homogeneous in the spectrum (identical degeneracies for all energy levels). In this note we present a model that can be solved by ``free fermions in disguise'' (FFD), such that the spectrum is free from exponential degeneracies for generic coupling constants. The model can be seen as a particular perturbation of two Ising chains. Alternatively, it can be realized as an interpolation between a standard Jordan-Wigner solvable chain and the original FFD model of Fendley. We used ChatGPT Pro 5.4 and 5.5 as a research assistant; in the Supplemental Material we provide details about the collaboration between the AI and the human author.
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cond-mat.stat-mech 1years
2026 1verdicts
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Correlation and entanglement dynamics of free fermions in disguise
Analytic method for GGE quasi-momentum distribution in degenerate free-fermion models plus a conjecture adjusting the quasi-particle entanglement formula, tested numerically with good agreement on local observables but small deviations on entanglement.