Adaptive Entanglement Witnessing for Two-Qubit Systems

@misc{gruber2026adaptive,
  title = {{Adaptive Entanglement Witnessing for Two-Qubit Systems}},
  author = {Lev Gruber and Ria Haapala and Elio Thadhani and Paco Navarro and Eritas Yang and Benjamin Hartley and Rebecca Verghese and Oscar Scholin and Isabel Godoy and Stuart Kerr and Brayden Mendoza and Alec Roberson and Theresa W. Lynn},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.16018},
  eprint = {2610.16018},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.16018},
}

TY  - UNPB
TI  - Adaptive Entanglement Witnessing for Two-Qubit Systems
AU  - Lev Gruber
AU  - Ria Haapala
AU  - Elio Thadhani
AU  - Paco Navarro
AU  - Eritas Yang
AU  - Benjamin Hartley
AU  - Rebecca Verghese
AU  - Oscar Scholin
AU  - Isabel Godoy
AU  - Stuart Kerr
AU  - Brayden Mendoza
AU  - Alec Roberson
AU  - Theresa W. Lynn
PY  - 2026
DA  - 2026/10/12
PB  - arXiv
DO  - 10.48550/arxiv.2610.16018
UR  - https://arxiv.org/abs/2610.16018
AB  - Entanglement witnesses are a key instrument in determining the entanglement of unknown bipartite qubit systems without requiring a full tomography. Riccardi et al. (2020) proposed a set of two-qubit witnesses, denoted {W^3}, which require a set of local measurements in three bases. In this work we propose an additional set of witnesses, denoted {W^5}, that build on {W^3} and require measurements in two additional bases. We present an adaptive two-step method that uses the measurement results obtained for {W^3} to select which W^5 to evaluate. We computationally demonstrate that our adaptive two-step protocol can identify 72% of entangled states generated according to the methods of Roik et al. (2021) while requiring measurements in only five of the nine bases needed for full quantum tomography. Additionally, we experimentally verify the behavior of both sets of witnesses using polarization-entangled photon pairs.
ER  -