Quantum Theory Over Dual-Complex Numbers

We take quantum theory and replace C by C[ε] where ε 2 = 0, i.e. we extend quantum theory to the ring of dual complex numbers.The aim is to develop a common language in which to treat continuous quantum physics and discrete quantum models in a unified manner, including their symmetries.Since quantum theory is linear, introducing ε is enough to model infinitesimals.A first objection to this programme is that C[ε] is not a field, since division by ε is undefined, while quantum mechanics typically relies on division.A second objection concerns whether unitarity still makes sense given ε 2 = 0. Hence, the core of this work is dedicated to proving that dual-complex quantum theory remains fully consistent.In particular, norm is preserved at all times, and renormalization never requires dividing by an infinitesimal.An equivalence with conventional quantum theory is demonstrated: the dual-complex extension of a parametrized quantum operation automatically provides a linear treatment of its first-order variations.As a first example application, we provide a unified description of both the Dirac equation in the continuum and the Dirac Quantum Walk in the discrete.We establish the discrete Lorentz covariance of the latter.