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  • Open Access

Bundling of bipartite entanglement

Maike Drieb-Schön1,*, Florian Dreier1,2,†, and Wolfgang Lechner1,2

  • 1Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria
  • 2Parity Quantum Computing GmbH, A-6020 Innsbruck, Austria

  • *Contact author: maike.schoen@uibk.ac.at
  • †Contact author: f.dreier@parityqc.com
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Phys. Rev. A 114, 012401 – Published 1 July, 2026

DOI: https://doi.org/10.1103/ss6r-ktrr

Abstract

We investigate bipartite entanglement and prove that in constrained energy subspaces, the entanglement spectra of multiple bipartitions are the same across the whole subspace. We show that in quantum many-body systems the bipartite entanglement entropy is affected in such a way that it forms “bundles” under unitary time evolution. Leveraging the structure of the subspace, we present methods to verify whether the entanglement spectrum of two bipartitions is identical throughout the entire subspace. For the subspace defined by the parity embedding, we further provide an algorithm that can determine this in polynomial time.

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Phys. Rev. A 114, 012401– Published 1 July, 2026
  • Received 2 January 2026
  • Accepted 11 June 2026
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