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arXiv · 2512.22942

Random matrix prediction of average entanglement entropy in non-Abelian symmetry sectors

Anwesha Chakraborty·Lucas Hackl·Mario Kieburg
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Abstract

We study the average bipartite entanglement entropy of Haar-random pure states in quantum many-body systems with global $\mathrm{SU}(2)$ symmetry, constrained to fixed total spin $J$ and magnetization $J_z = 0$. Focusing on spin-$\tfrac12$ lattices and subsystem fractions $f < \frac{1}{2}$, we derive a asymptotic expression for the average entanglement entropy up to constant order in the system volume $V$. In addition to the expected leading volume law term, we prove the existence of a $\frac{1}{2}\log V$ finite-size correction resulting from the scaling of the Clebsch-Gordon coefficients and compute explicitly the $O(1)$ contribution reflecting angular-momentum coupling within magnetization blocks. Our analysis uses features of random matrix ensembles and provides a fully analytical treatment for arbitrary spin densities, thereby extending Page type results to non-Abelian sectors and clarifying how $\mathrm{SU}(2)$ symmetry shapes average entanglement.

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BibTeXRIS

Anwesha Chakraborty, Lucas Hackl, Mario Kieburg. 2025-12-28. Random matrix prediction of average entanglement entropy in non-Abelian symmetry sectors. https://arxiv.org/abs/2512.22942

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