Full-Rank Noise Forbids Long-Range Entanglement Swapping

@misc{trinh2026fullrank,
  title = {{Full-Rank Noise Forbids Long-Range Entanglement Swapping}},
  author = {Xuan Du Trinh and Nicholas Pardave and Angie Huang and Xiangyi Meng and Nengkun Yu},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.11021},
  eprint = {2609.11021},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.11021},
}

TY  - UNPB
TI  - Full-Rank Noise Forbids Long-Range Entanglement Swapping
AU  - Xuan Du Trinh
AU  - Nicholas Pardave
AU  - Angie Huang
AU  - Xiangyi Meng
AU  - Nengkun Yu
PY  - 2026
DA  - 2026/09/10
PB  - arXiv
DO  - 10.48550/arxiv.2609.11021
UR  - https://arxiv.org/abs/2609.11021
AB  - Quantum repeaters extend entanglement by swapping noisy elementary links. We prove that full-rank noise forbids this at long range: for any entangled full-rank two-qubit link, there is a finite depth beyond which no end-to-end entanglement can be established regardless of the measurement outcomes on intermediate qubits, even under any adaptive postselected strategy. This limit is set by one spectral parameter of the link, giving a no-go criterion for repeater routing. In contrast, we construct link state families of rank three and rank two that admit postselected measurement outcome branches of exponentially small probability but with strictly positive concurrence at every finite depth. Swapping experiments on a superconducting processor show that links of equal initial concurrence but different rank behave differently under postselected swapping. In the language of many-body physics, the chain is a matrix-product density operator, and full-rank bonds forbid long-range localizable entanglement, while rank-deficient bonds can sustain it.
ER  -