Robust Quantum Memory Advantage from Contextuality

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 $N=\chi(G)$ states, where $\chi(G)$ 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 $d=\xi(G)+1$, where $\xi(G)$ is the graph's orthogonal rank.

This separation scales exponentially ($d=\mathcal O(n)$ versus $N=2^{\Omega(n)}$) for Boolean-orthogonality graphs.

Crucially, this memory advantage maintains an $\mathcal{O}(1)$ threshold against both depolarizing and coherent noise.