The coRE-hardness conjecture for distinguishing commuting quantum game values

Let G\mathcal{G} be a game, and let ωqc(G)\omega_{\mathrm{qc}}(\mathcal{G}) denote its commuting quantum value. Consider the promise problem in which

ωqc(G)=1orωqc(G)≤14.\omega_{\mathrm{qc}}(\mathcal{G})=1\qquad\text{or}\qquad\omega_{\mathrm{qc}}(\mathcal{G})\leq \frac{1}{4}.

CoRE-hardness conjecture. Deciding which of these two cases holds is coRE\mathrm{coRE}-hard; equivalently, MIPco=coRE\mathrm{MIP}^{\mathrm{co}}=\mathrm{coRE}.

This conjecture supplies the hardness premise needed to construct games whose finite-level NPA scores substantially exceed their true commuting quantum values. Its status is not resolved in the supplied source.

References

Primary source

Igor Klep, Connor Paddock, Marc-Olivier Renou, Simon Schmidt, Lucas Tendick, Xiangling Xu and Yuming Zhao, “Quantitative Quantum Soundness for Bipartite Compiled Bell Games via the Sequential NPA Hierarchy”, arXiv:2507.17006 (2026).

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