The ubit model in real-amplitude quantum theory

The logical structure of quantum theory is unchanged if we replace the usual complex probability amplitudes with real amplitudes, but the physics is in general quite different. Here we consider a specific model within real-amplitude quantum theory in which a hypothetical binary quantum system, the ubit, substitutes for the complex phase factors of the standard theory. In a certain limit, this model yields an effective theory that looks very much like ordinary quantum theory, but it differs in that it exhibits spontaneous decoherence of isolated systems.