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Discrete Interaction Lattices and Split-Step Symmetry A Structural Correspondence Between Tukutuku Weaving and Quantum Walk Models

Darren Cudd

Published Mar 27, 2026• 0 citations
Publisher

Abstract

This paper introduces a discrete interaction lattice derived from the directed geometry of tukutuku weaving and formulates it as a two-component unitary dynamical system. It is shown that the lattice recovers the 1+1 dimensional Dirac equation in the continuum limit, establishing a rigorous connection to relativistic quantum dynamics. At the discrete level, however, a structural obstruction emerges: a sign-flip interface fails to support a localized zero-mode due to broken chiral symmetry. This failure is identified as a fundamental limitation of the single-step model, leading to the necessity of a period-2 staggered lattice and a symmetrized split-step formulation. The work provides a mathematically grounded framework while clearly distinguishing proven results from heuristic structural correspondence.

DOI
10.5281/zenodo.19247851

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This paper introduces a discrete interaction lattice derived from the directed geometry of tukutuku weaving and formulates it as a two-component unitary dynamical system. It is shown that the lattice recovers the 1+1 dimensional Dirac equation in the continuum limit, establishing a rigorous connection to relativistic quantum dynamics. At the discrete level, however, a structural obstruction emerges: a sign-flip interface fails to support a localized zero-mode due to broken chiral symmetry. This failure is identified as a fundamental limitation of the single-step model, leading to the necessity of a period-2 staggered lattice and a symmetrized split-step formulation. The work provides a mathematically grounded framework while clearly distinguishing proven results from heuristic structural correspondence.
It has been observed that quantum walks on regular lattices can give rise to wave equations for relativistic particles in the continuum limit. In this paper, we define the three-dimensional discrete-time walk as a product of three coined one-dimensional walks. The factor corresponding to each one-dimensional walk involves two projection operators that act on an internal coin space; each projector is associated with either the ``forward'' or ``backward'' direction in that physical dimension. We show that the simple requirement that there is no preferred axis or direction along an axis---that is, that the walk be symmetric under parity transformations and steps along different axes of the cubic lattice be uncorrelated---leads, in the case of the simplest solution, to the requirement that the continuum limit of the walk is fully Lorentz-invariant. We show further that, in the case of a massive particle, this symmetry requirement necessitates the use of a four-dimensional internal space (as in the Dirac equation). The ``coin flip'' operation is generated by the parity transformation on the internal coin space, while the differences of the projection operators associated with each dimension must all anticommute. Finally, we discuss the leading correction to the continuum limit, and the possibility of distinguishing through experiment between the discrete random walk and the continuum-based Dirac equation as a description of fermion dynamics.
Discrete quantum walks are periodically driven systems with discrete time evolution. In contrast to ordinary Floquet systems, no microscopic Hamiltonian exists, and the one-period time evolution is given directly by a series of unitary operators. Regarding each constituent unitary operator as a discrete time step, we formulate discrete space-time symmetry in quantum walks and evaluate the corresponding symmetry protected topological phases. In particular, we study chiral and/or time-glide symmetric topological quantum walks in this formalism. Due to the discrete nature of time evolution, the topological classification is found to be different from that in conventional Floquet systems. As a concrete example, we study a two-dimensional quantum walk having both chiral and time-glide symmetries and identify the anomalous edge states protected by these symmetries.
Dirac particle represents a fundamental constituent of our nature. Simulation of Dirac particle dynamics by a controllable quantum system using quantum walks will allow us to investigate the non-classical nature of dynamics in its discrete form. In this work, starting from a modified version of one-spatial dimensional general inhomogeneous split-step discrete quantum walk we derive an effective Hamiltonian which mimics a single massive Dirac particle dynamics in curved (1 + 1) space-time dimension coupled to U (1) gauge potential—which is a forward step towards the simulation of the unification of electromagnetic and gravitational forces in lower dimension and at the single particle level. Implementation of this simulation scheme in simple qubit-system has been demonstrated. We show that the same Hamiltonian can represent (2 + 1) space-time dimensional Dirac particle dynamics when one of the spatial momenta remains fixed. We also discuss how we can include U ( N ) gauge potential in our scheme, in order to capture other fundamental force effects on the Dirac particle. The emergence of curvature in the two-particle split-step quantum walk has also been investigated while the particles are interacting through their entangled coin operation.
A discrete-time Quantum Walk (QW) is essentially a unitary operator driving the evolution of a single particle on the lattice. Some QWs admit a continuum limit, leading to familiar PDEs (e.g. the Dirac equation), and thus provide us with discrete toy models of familiar particles (e.g. the electron). In this paper, we study the continuum limit of a wide class of QWs, and show that it leads to all those PDEs corresponding to the Hamiltonian form of the massive curved Dirac equation in (1 + 1) dimensions. Therefore a certain QW, which we make explicit, provides us with a unitary discrete toy model of the electron as a test particle in curved spacetime, in spite of the fixed background lattice. Mathematically we have introduced two novel ingredients for taking the continuum limit of a QW, but which apply to any quantum cellular automata: encoding and grouping.
Discrete-time quantum walks (DTQW) have topological phases that are richer than those of time-independent lattice Hamiltonians. Even the basic symmetries, on which the standard classification of topological insulators hinges, have not yet been properly defined for quantum walks. We introduce the key tool of time frames, i.e., we describe a DTQW by the ensemble of time-shifted unitary time-step operators belonging to the walk. This gives us a way to consistently define chiral symmetry (CS) for DTQW's. We show that CS can be ensured by using an ``inversion symmetric'' pulse sequence. For one-dimensional DTQW's with CS, we identify the bulk $\mathbb{Z}\ifmmode\times\else\texttimes\fi{}\mathbb{Z}$ topological invariant that controls the number of topologically protected 0 and $\ensuremath{\pi}$ energy edge states at the interfaces between different domains, and give simple formulas for these invariants. We illustrate this bulk-boundary correspondence for DTQW's on the example of the ``4-step quantum walk,'' where tuning CS and particle-hole symmetry realizes edge states in various symmetry classes.
A discrete-time quantum walk (DTQW) is a lattice model of a single particle whose two-component internal state is repeatedly mixed by a unitary "coin" and shifted in space, chirality by chirality. In this work, we present a framework for coupling such a walk to a background electromagnetic (U(1)) gauge field. Instead of introducing traditional link variables common to the existing literature, we embed the gauge phase directly within the coin operator already required by the free walk, thereby eliminating the need for extra local degrees of freedom. We demonstrate this construction in two stages: first, using only coin phases to generate a purely spatial potential (A_1) while structurally forcing the temporal potential (A_0) to vanish (the temporal, or Weyl, gauge); and second, incorporating a single post-shift phase to recover a fully general potential (A_mu = (A_0, A_1). In both regimes, we show that the gauge transformation law for the coin phases is rigorously forced by the consistency requirement between the left- and right-moving sectors rather than assumed. We verify the construction non-perturbatively through the exact lattice dispersion relation, the walk’s convergence rate to the continuum Dirac equation, and its intrinsic avoidance of the fermion doubling problem.