Entangling power and fidelity diagnostic for bipartite quantum channels
Abstract
We study two distinct diagnostics of bipartite quantum channels: the average fidelity between a desired state and noisy output across different classes of input states, and generation of entanglement from pure product input states, quantified by well-defined entangling power. These diagnostics are generally independent, but together they provide a more complete description of bipartite channels. We show that the fidelity averaged over any local-unitary orbit with fixed Schmidt coefficients for equal local dimensions is completely determined by the average input-output fidelity and its restriction to product inputs. We also introduce concurrence- and negativity-based entangling power for two-qubit channels, prove their convexity and monotonicity under local postprocessing, and show that, unlike the previously proposed linear-entropy quantity, they vanish for all separable channels. Representative separable and nonseparable channels are investigated. Finally, we generalize our definitions of entangling power to nonproduct inputs, and provide an analytical lower bound for the concurrence-based entanglement variation, showing its effectiveness with specific examples.
Versions
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BibTeX
@misc{rudzinski2026entangling,
title = {{Entangling power and fidelity diagnostic for bipartite quantum channels}},
author = {Marcin Rudziński and Gianluigi Tartaglione and Karol Życzkowski},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2605.26867},
eprint = {2605.26867},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.26867},
}
RIS
TY - UNPB
TI - Entangling power and fidelity diagnostic for bipartite quantum channels
AU - Marcin Rudziński
AU - Gianluigi Tartaglione
AU - Karol Życzkowski
PY - 2026
DA - 2026/09/29
PB - arXiv
DO - 10.48550/arxiv.2605.26867
UR - https://arxiv.org/abs/2605.26867
AB - We study two distinct diagnostics of bipartite quantum channels: the average fidelity between a desired state and noisy output across different classes of input states, and generation of entanglement from pure product input states, quantified by well-defined entangling power. These diagnostics are generally independent, but together they provide a more complete description of bipartite channels. We show that the fidelity averaged over any local-unitary orbit with fixed Schmidt coefficients for equal local dimensions is completely determined by the average input-output fidelity and its restriction to product inputs. We also introduce concurrence- and negativity-based entangling power for two-qubit channels, prove their convexity and monotonicity under local postprocessing, and show that, unlike the previously proposed linear-entropy quantity, they vanish for all separable channels. Representative separable and nonseparable channels are investigated. Finally, we generalize our definitions of entangling power to nonproduct inputs, and provide an analytical lower bound for the concurrence-based entanglement variation, showing its effectiveness with specific examples.
ER -