Asymptotic properties of the Dirac quantum cellular automaton

TL;DR

This paper analyzes the Dirac quantum cellular automaton, showing its similarities to quantum walks, deriving its asymptotic behavior, and demonstrating its entanglement properties, thus providing a new perspective on quantum lattice models.

Contribution

It introduces the Dirac quantum cellular automaton as an alternative to quantum walks, with controllable dispersion and asymptotic properties, and connects it to the Dirac Hamiltonian.

Findings

The automaton shares properties with quantum walks.

The Dirac Hamiltonian is recovered in a specific limit.

Asymptotic entanglement exceeds quantum walk limits.

Abstract

We show that the Dirac quantum cellular automaton [Ann. Phys. 354 (2015) 244] shares many properties in common with the discrete-time quantum walk. These similarities can be exploited to study the automaton as a unitary process that takes place at regular time steps on a one-dimensional lattice, in the spirit of general quantum cellular automata. In this way, it becomes an alternative to the quantum walk, with a dispersion relation that can be controlled by a parameter, which plays a similar role to the coin angle in the quantum walk. The Dirac Hamiltonian is recovered under a suitable limit. We provide two independent analytical approximations to the long term probability distribution. It is shown that, starting from localized conditions, the asymptotic value of the entropy of entanglement between internal and motional degrees of freedom overcomes the known limit that is approached by the quantum walk for the same initial conditions, and are similar to the ones achieved by highly localized states of the Dirac equation.