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X States of the Same Spectrum and Entanglement as All Two-Qubit States

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arxiv 1802.03038 v1 pith:GKDJ2QUI submitted 2018-02-08 quant-ph

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keywords statesexplicitfamilytwo-qubitentanglementexistencegeneralsame
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We present an explicit family of two-qubit X states with entanglement-preserving unitary (EPU) equivalence to the set of general states; that is, for any spectrum-entanglement combination achievable by general states, this family contains an X state of the same spectrum and entanglement. This idea was originally conjectured by the author and supported with strong numerical evidence in arXiv:1310.7038. Then, in Ann. Phys. 351 (2014) 79, the authors proved the existence of such two-qubit unitary transformations, but found the parameters to be transcendental, eluding explicit solution. Here, by a different method, we prove the existence of such transformations, obtain a compact implicit solution for them, and provide an exact, explicit form of the desired X-state family.

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Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Local-available quantum correlation swapping in one-parameter X states

    quant-ph 2025-07 reject novelty 5.0 of 10

    LAQC can be redistributed by projective swapping in X states, but the paper's key examples claiming separable final states with nonzero LAQC are only valid for part of the parameter space.

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