  $\bf{Abstract}$: 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.
