Why do quantum reservoir computers actually outperform classical ones?

Any reservoir computer using linear dynamics and linear readout can't generate new predictive power beyond what's already in its inputs — it just reshuffles information. This fundamental ceiling is easy to miss because total capacity metrics blur contributions across time delays. Crucially, single-photon quantum operations provably exceed this limit, offering the clearest demonstration yet of real quantum advantage in reservoir computing and a practical test for detecting non-Gaussian behavior in quantum systems.