Some Comments on Unitary Qubit Lattice Algorithms for Classical Problems

$\mathbf{A}\mathbf{b}\mathbf{s}\mathbf{t}\mathbf{r}\mathbf{a}\mathbf{c}\mathbf{t}$: A qubit lattice algorithm (QLA), which consists of a set of interleaved unitary collision-streaming operators, is developed for electromagnetic wave propagation in tensor dielectric media. External potential operators are required to handle gradients in the refractive indices, and these operators are typically non-unitary. A similar problem arises in the QLA for the Korteweg-de Vries equation, as the potential operator that models the KdV nonlinear term is also non-unitary. Several QLAs are presented here that avoid the need of this non-unitary potential operator by perturbing the collision operator. These QLAs are fully unitary.