Robust Quantum Memory Advantage from Contextuality

Abstract

Quantum contextuality is widely recognized as an essential non-classical resource underlying quantum technology, yet illuminating the precise mechanisms through which it translates into unconditional computational advantages remains an ongoing challenge. We demonstrate an exponential, noise-resilient memory advantage for quantum finite automata arising from graph-theoretic approaches to contextuality. We define a promise problem on an exclusivity graph $G$ for which any classical deterministic automaton acts as a non-contextual hidden variable model requiring at least $N=χ(G)$ states, where $χ(G)$ is the graph's chromatic number. In contrast, by exploiting a structural phenomenon we term \textit{representational contextuality}, a QFA solves this task using a memory of dimension at most $d=ξ(G)+1$, where $ξ(G)$ is the graph's orthogonal rank. This separation scales exponentially ($d=\mathcal O(n)$ versus $N=2^{Ω(n)}$) for Boolean-orthogonality graphs. Crucially, this memory advantage maintains an $\mathcal{O}(1)$ threshold against both depolarizing and coherent noise.