Spekkens' Toy Model, Finite Field Quantum Mechanics, and the Role of Linearity

We map Spekkens' toy model to a quantum mechanics defined over the finite field $F_5$. This allows us to define arbitrary linear combinations of the epistemic states in the model. For Spekkens' elementary system with only 2² = 4 ontic states, the mapping is exact and the two models agree completely. However, for a pair of elementary systems there exist interesting differences between the entangled states of the two models. (paper)