Quantum theory over dual-complex numbers

TL;DR

This paper extends quantum theory to dual-complex numbers, enabling a unified treatment of continuous and discrete quantum models while ensuring mathematical consistency and preserving core quantum properties.

Contribution

It introduces a consistent dual-complex extension of quantum theory that models infinitesimals without losing unitarity or requiring division by infinitesimals.

Findings

Norm is preserved in dual quantum theory.

Renormalization avoids dividing by infinitesimals.

Unified description of Dirac equation and quantum walk.

Abstract

We take quantum theory and replace $\mathbb{C}$ by $\mathbb{C}[\varepsilon]$ where $\varepsilon^2=0$, 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 $\varepsilon$ is enough to model infinitesimals. A first objection to this programme is that $\mathbb{C}[\varepsilon]$ is not a field, since division by $\varepsilon$ is undefined, while quantum mechanics typically relies on division. A second objection concerns whether unitarity still makes sense given $\varepsilon^2 = 0$. Hence, the core of this work is dedicated to proving that \dual 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 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.