A Noncommutative Nullstellensatz for Perfect Two-Answer Quantum Nonlocal Games
Tianshi Yu, Lihong Zhi
TL;DR
This work introduces a noncommutative Nullstellensatz in the context of perfect two-answer quantum nonlocal games. It proves that a two-answer game with a perfect commuting-operator strategy also has a perfect classical strategy, extending finite-dimensional results to infinite-dimensional settings. The result is formulated via the universal game algebra $\mathcal{A}$, a left ideal $\mathcal{L}(\mathcal{N})$, and an Archimedean sums-of-squares cone $\mathrm{SOS}_{\mathcal{A}}$, yielding a one-dimensional representation that annihilates the invalid set $\mathcal{N}$; this establishes a noncommutative Nullstellensatz in this special case and links commuting-operator strategies to deterministic classical strategies. The findings illuminate the algebraic structure of perfect strategies and delineate the scope and limits of the approach, especially noting the constraint to two answers and infinite-dimensional settings.
Abstract
This paper introduces a noncommutative version of the Nullstellensatz, motivated by the study of quantum nonlocal games. It has been proved that a two-answer nonlocal game with a perfect quantum strategy also admits a perfect classical strategy. We generalize this result to the infinite-dimensional case, showing that a two-answer game with a perfect commuting operator strategy also admits a perfect classical strategy. This result induces a special case of noncommutative Nullstellensatz.
