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◇ arXiv2026-09-09· quant-ph

Unbounded degree overhead for Alice-conditioned quantum Bell certificates

Fumin Wang

原始摘要(英文原文)· Original abstract
Requiring each sum-of-squares term to involve only one of Alice's measurement questions can impose an unbounded certification cost. In the simplest Bell scenario, we prove that no finite level of the Alice-conditioned NPA hierarchy contains all standard level-two Bell certificates. An explicit family of truncated positive functionals on the infinite dihedral group exceeds the tilted-CHSH quantum bound at every prescribed finite level, while a standard degree-two certificate is exact. A Fejer-weighted trace reduces positivity to a rank-one subtraction from a moving-average Gram matrix. The required conditioned level grows at least as $(2-α)^{-1/2}$ near the endpoint tilt. This bounds the degree of exact nice-SOS inputs to compiled-game soundness proofs. Consequently, no finite conditioned level certifies the entire optimal CHSH randomness tradeoff against quantum side information, although standard level two does. Away from the endpoint, we prove a sharp one-level cost throughout $α\in[13/10,3/2]$, using optimal-strategy kernels and exact Bernstein matrix positivity to certify a continuous interval. The results separate ordinary SOS degree from the resources keyed by single-question certificate structure.
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Unbounded degree overhead for Alice-conditioned quantum Bell certificates — 科研速览 Science Skim