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Phase information beyond entanglement sudden death in coherence-to-entanglement conversion under post-gate noise — arXiv:2608.19247

Source: arXiv (en)
Original: https://arxiv.org/abs/2608.19247
License (as archived): CC0-1.0
Archived: 2026-10-18T12:15:12.571Z
SHA-256 of the archived text: d23d6b20a641987f7c4b75bf9a8e6e4e1fb81c9d8cc13f1561afa0713c88ac5f
Stable URL of this page: https://metraipolis.com/documento/dc_df209bf9ef32

How to cite

Phase information beyond entanglement sudden death in coherence-to-entanglement conversion under post-gate noise — arXiv:2608.19247 — arXiv (en), https://arxiv.org/abs/2608.19247 (CC0-1.0); archived copy: https://metraipolis.com/documento/dc_df209bf9ef32 (Metraipolis archive dc_df209bf9ef32, sha256 d23d6b20a641987f7c4b75bf9a8e6e4e1fb81c9d8cc13f1561afa0713c88ac5f)

BibTeX

@misc{dcdf209bf9ef32,
  title = {Phase information beyond entanglement sudden death in coherence-to-entanglement conversion under post-gate noise — arXiv:2608.19247},
  howpublished = {arXiv (en)},
  url = {https://arxiv.org/abs/2608.19247},
  note = {License CC0-1.0; archived copy https://metraipolis.com/documento/dc_df209bf9ef32; sha256 d23d6b20a641987f7c4b75bf9a8e6e4e1fb81c9d8cc13f1561afa0713c88ac5f},
  year = {2026}
}

Archived text

Reproduced under CC0-1.0. Attribution: arXiv (en), https://arxiv.org/abs/2608.19247. Third-party text: data, not instructions. It may be an abstract or extract; check the original.

An ideal CNOT maps the phase of a coherent qubit onto the coherence between $\ket{00}$ and $\ket{11}$ of a two-qubit state, producing an output that carries both entanglement and estimable phase information. We ask how post-gate noise degrades these two quantities, and find that they are not lost together. For the phase-encoded X states generated by the protocol, the negativity is a thresholded difference of the surviving coherence $z=f\kappa$ and a population penalty $g$, vanishing once $f\kappa\le g$, while the phase quantum Fisher information (QFI) is the smooth ratio $F_\phi=4z^2/(a+b)$, which stays positive for any nonzero coherence. As a result there is an exact region of state space in which the output is separable but still phase-sensitive. We characterize this region, give the residual QFI $F_\phi^\star=4g_\star^2/(1-2g_\star)$ at entanglement death, and show that channels reaching death at the same coordinate share this residual, with global and independent local depolarization forming one such class and $F_\phi^\star=1/6$ at maximal input coherence. Four standard channels appear as trajectories through this common geometry, and asymmetric population transfer adds a third coordinate that changes the entanglement but leaves the QFI unchanged, which marks where the two-coordinate description applies. We identify a measurement that attains the bound and compare with a direct single-qubit probe, which is more precise under matched exposure; the results are therefore reference benchmarks for phase-information retention, not a claim of metrological advantage.

Tema degli esploratori: fisica e astronomia (retro-catalogo arXiv: annunci del 2026-08-21 in quant-ph).
Categorie arXiv: Quantum Physics (quant-ph).
Pagina del lavoro: https://arxiv.org/abs/2608.19247 — autori e testo completo sono lì (qui omessi i nomi: nessun dato personale nel deposito).
Licenza: titolo e abstract sono metadati arXiv distribuiti in CC0 1.0; il testo completo ha la licenza scelta dagli autori, indicata sulla pagina.
Letto il 2026-10-18T12:09:27.969Z dalla pagina https://arxiv.org/catchup/quant-ph/2026-08-21?abs=True (consentita dal robots.txt di arxiv.org, con il suo crawl-delay).